Lake Preservation & Restoration Concepts - Tuolumne Utilities District

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Lake Preservation & Restoration Concepts - Tuolumne Utilities District

Chapter 3 - Part ILake Preservation & Restoration ConceptsPhoenix Lake Preservation & Restoration Plan


D EUSE OF DOCUMENTSTHIS DOCUMENT, INCLUDING THEINCORPORATED DESIGNS, IS ANINSTRUMENT OF SERVICE FORTHIS PROJECT AND SHALL NOT BEUSED FOR ANY OTHER PROJECTWITHOUT THE WRITTENAUTHORIZATION OF T.U.D.DOCUMENT RELEASEREV EWREV S ON NOTESDES GNEDSLDDRAWNSLDREV EWEDCTHAPPROVEDCTHPREPARED BYSONORA, CA 95370 (209) 532-553618885 NUGGET BLVD.TUOLUMNEUTILITIESDISTRICTPREPARED FORLAKE MANAGEMENT UNITSPHOENIX LAKEPRESERVATION ANDRESTORATION PLANSONORA CAL FORN A238023752380238023752375N0 200' 400' 800'2370 2375238023802375238023702375237523802370237523701234A B CFILE NAMEMgt Units.dwgJOB NUMBER10-1019DATEJune, 2011FIGURE3.1-1


Chapter 3 – Part IIn the 1980s, two dredging projects took placeon the lake. A photograph from 1981 showsPhoenix Lake drained and constructionequipment removing sediment from the lake.The report associated with this photographnotes that sediment removed from the lake wasused to reinforce the dam (Mother Lode DistrictGas & Water Department, 1982). In 1986,Tuolumne County conducted a suction dredgingproject on the lake. Material from this dredgingevent was placed on the north side of the lake(Figure 3.1‐1). The total volume of sedimentremoved from the lake during these projects isnot known, but is estimated to be as much as300,000 cubic yards (cy) (Pers. Comm., Allen2011).In 1983, Tuolumne County purchased a watersystem from the Pacific Gas and ElectricCompany (PG&E) which included Phoenix Lakewater rights and facilities, as well as portions ofthe lake. The TUD was formed in 1992 tocombine the Tuolumne Water System andTuolumne Regional Water District into oneagency; the water system including PhoenixLake was transferred from the County to TUD.No additional dredging has occurred since 1992under TUD’s managment. The TUD’s generaloperations of the lake are described in thefollowing section.2.2 Lake Hydrology & OperationsThe major drainages that feed Phoenix Lake areSullivan, Power and Chicken creeks. There aretwo, smaller unnamed watersheds that drain tothe southern side of Phoenix Lake. In thisreport, these unnamed drainages are referredto as Ridgewood and Phoenix Lake Park.Inflow to Phoenix Lake is dominated by naturalrunoff from the major drainages, with thegreatest volume of runoff occurring in the wetseason (November through April). However,3.1‐3Lake Preservation & Restoration Conceptsthere are also substantial out‐of‐basindiversions from the South Fork Stanislaus Riverwhich feed the lake year‐round. Water istransferred from Lyons Reservoir on the SouthFork Stanislaus via the Main Tuolumne Canal toa penstock that connects to PG&E’s PhoenixPowerhouse in the Power Creek watershed.Between 4 to 30 cfs are regularly passedthrough the powerhouse and discharged toPower Creek. The TUD is able to divert a portionof the water released to Power Creek to itswater supply treatment and distribution systemthrough a system of canals and pipes thatbypass Phoenix Lake. The water remaining inPower Creek is discharged to Phoenix Lake. TheTUD also has an intake tower in Phoenix Lakethat transfers water to the four treatmentplants that supply the communities of Sonora,Jamestown, Scenic View and Mono Village.Water surface elevation in Phoenix Lake islargely dictated by manual operation of aflashboard weir and outlet gates located at thereservoir spillway (Figure 3.1‐1). Themanagement of the flashboards controls thelarge‐scale, seasonal fluctuations of lake levels;operations of a spillway gate and a smaller fishflowbypass gate produce more modestadjustments in water surface elevation.The flashboard weir operations follow aseasonal protocol set by the California Divisionof Safety of Dams (DSOD). The TUD cannotinstall the flashboards prior to May 15, and theymust be removed by November 1. Installing theflashboards raises the elevation of the spillwayweir by approximately 6 ft (Photo 3.1‐2). Thisraises the lake water surface elevation toapproximately 2,385 ft above MSL, which is theordinary summer lake level (OSLL). Lake watersurface elevation data collected for this studyindicate that there are relatively minor (0.5 to 1ft) fluctuations of lake level during the summermonths (See Technical Appendix II).


Chapter 3 – Part ILake Preservation & Restoration ConceptsPLPRP to help quantify the flow rates into andout of the lake. These data and supportinganalyses are presented in Technical Appendix IIof the PLPRP.2.3 Bathymetry, Sedimentation andCapacityPhoto 3.1‐2. Flashboards being installed at the Spillwayweir in 2008. The lake level will rise to the top of theflashboards, which is equivalent to the Ordinary SummerLake Level (Photo from PLTF, 2010a).In October of each year the flashboards areremoved (Photo 3.1‐3), which lowers watersurface elevation to the ordinary winter lakelevel (OWLL) of approximately 2,379 ft aboveMSL. Lake water surface elevation datacollected for this study indicate that winterstorm events typically produce relatively smallincreases in lake level (approximately 1‐2 ft),and that water surface elevation drops rapidlyfollowing the storm event (See TechnicalAppendix II).Photo 3.1‐3. Spillway weir without flashboards in place,which is equivalent to the Ordinary Winter Lake Level.Several other factors also influence lake watersurface elevation, including: PhoenixPowerhouse operations, TUD bypass and intaketower operations, direct precipitation,evaporation and infiltration. Lake level andstreamflow data were collected as part of theBathymetryA bathymetric survey of Phoenix Lake wascompleted by TUD in 2002. Portions of the lakewere resurveyed in 2010 as part of the PLPRP.Figure 3.1‐2 shows lake bathymetry based on acompilation of the 2002 and 2010 survey data.The survey data show that most of the easternportion of the lake is 5 ft deep or less at OWLL.The western portion of the lake is shallow in theSpillway Unit (1‐2 ft deep at OWLL), with deepersections in the West Pool and 1986 dredge hole(8‐12 ft deep at OWLL). Maximum lake depth,measured at the TUD intake tower, isapproximately 25 ft at OWLL.Sedimentation Patterns and RatesFigure 3.1‐2 shows the change in elevationbetween 2002 and 2010 for unvegetatedportions of the lake. Figure 3.1‐2 indicates thatthe eastern portion of the lake largelyexperienced aggradation on the order of 0.1 to1.0 ft during this time period. In comparison,the western portion of the lake saw morevariable erosion and deposition patterns. Thisis because the eastern portion (i.e., the EastPool and Boot Units) of the lake largely receivesdeposition of fines that are suspended in thewater column (See Section 2.4 for discussion).Whereas, the West Pool receives coarsesediment delivered directly from Sullivan,Chicken and Power creeks. Significant erosionand deposition near the sandbar area can beexplained by migration of the Sullivan Creekchannel within the lake.3.1‐4


D EUSE OF DOCUMENTSTHIS DOCUMENT, INCLUDING THEINCORPORATED DESIGNS, IS ANINSTRUMENT OF SERVICE FORTHIS PROJECT AND SHALL NOT BEUSED FOR ANY OTHER PROJECTWITHOUT THE WRITTENAUTHORIZATION OF T.U.D.DOCUMENT RELEASEREV EWREV S ON NOTESDES GNEDSLDDRAWNSLDREV EWEDCTHAPPROVEDCTHPREPARED BYLAKE OUTLINE2010 BATHYMETR C SURVEYS 18885 NUGGET BLVD. SONORA, CA 95370 (209) 532-5536TUOLUMNEUTILITIESDISTRICTPREPARED FORPHOENIX LAKEPRESERVATION ANDRESTORATION PLANCOMPAR SON OF 2002 ANDSONORA CAL FORN A1234A B CNOTES:1. ELEVATIONS LISTED REPRESENT THE DIFFERENCE IN ELEVATION, RELATIVE TO2002 SURVEY DATA.2. NEGATIVE NUMBERS INDICATE NET EROSION. POSITIVE NUMBERS INDICATENET DEPOSITION.3. AREAS WITH NO COLOR FILL INDICATE NO NET CHANGE IN ELEVATION.NFILE NAMEVOL COMP OVRLJOB NUMBER10-1019DATEFEB-2011FIGUREMARSH AREA BORDER, TYP.APPROXIMATE 2002 MID-LAKE RIDGELINEAPPROXIMATE 2010 MID-LAKE RIDGELINE0 150' 300' 600'3.1-2LIMIT OF 2010 SURVEY DATA


Chapter 3 – Part IComparison of the 2002 and 2010 bathymetricsurveys suggest that the net average annualsedimentation rate exceeds 4,600 cy per year(See Technical Appendix I). While this estimateonly includes volume comparisons for areasthat were resurveyed in 2010 (Figure 3.1‐2),field observations suggest that the vast majorityof sedimentation has occurring in these areas.This is because significant deposition occurs inthe winter season when the lake level is lowest.At those times, even high flows do not flood thewetlands in the North Marsh. Hence, significantsedimentation in the North Marsh is not likelyto occur, and no evidence of widespreaderosion was observed. Similarly, much of theBoot Unit also is above the OWLL and is nottypically flooded by sediment‐laden winterrunoff, but the Boot Unit does appear to beaggrading and expanding, particularly in areasclosest to the East Pool.Storage CapacityThe 2002 and 2010 survey data were also usedto calculate lake volume and usable storagecapacity, which are summarized in Table 3.1‐1.Table 3.1‐1. Summary of Phoenix LakeVolume and Usable Storage CapacityStorageCondition(ac‐ft)2010 Lake Capacity 600.22002 Lake Capacity 623.3Difference in Capacity ‐23.12010 Usable Storage – Summer 517.62002 Usable Storage – Summer 527.2Difference in Usable Storage ‐9.72010 Usable Storage – Winter 108.32002 Usable Storage – Winter 118.0Difference in Usable Storage ‐9.7The current lake capacity is estimated to be 600ac‐ft, a reduction of approximately 23 ac‐ftsince 2002. However, not all of the lake volumeis usable storage. The mid‐lake ridge thatLake Preservation & Restoration Conceptsseparates the East and West Pools creates“dead storage” in the East Pool below elevation2,377 ft (i.e., water in the East Pool cannotreach the intake structure in the West Pool dueto lakebed topography). Smaller amounts ofdead storage occur in the West Pool, 1986dredge hole in the western portion of the lake,and portions of the North Marsh. Consequently,usable storage is substantially less than thetotal impounded lake volume.2.4 GeomorphologyThis section describes landforms and fluvialgeomorphic processes that influencesedimentation patterns within the lake. Thegeomorphology of the Phoenix Lake watershedis described in detail in Chapter 2 of the PLPRP.Pre‐dam LandformsThere are no survey records or photographsthat document the landforms that existed in thefootprint of Phoenix Lake prior to constructionof the dam. It is hypothesized that theconfluence of Sullivan, Chicken and Powercreeks was an unconfined, relatively lowgradient alluvial valley. Downstream of thisconfluence it is believed that Sullivan Creekbecame confined by the ridge in the lake andhillslopes to the west (current location of AppleValley Estates). This assertion is supported bythe considerable depth of the West Pool,bedrock exposures near the spillway, the heightof the dam, and the morphology of the SullivanCreek valley downstream of the lake.The eastern portion of the lake (i.e., East Pooland Boot Units, Figure 3.1‐1) was likely a wetmeadow that collected runoff and sedimentfrom the Ridgewood and Phoenix Lake Parkwatersheds. To a certain degree, the ridge inthe lake likely impounded water and sedimentdelivered from the drainages to the east. Thisassumption is supported by the relatively3.1‐6


Chapter 3 – Part ILake Preservation & Restoration Conceptsshallow, uniform configuration of the East Pool.Furthermore, this description may explainreports of the “two dams” that are alluded to inhistorical accounts of Phoenix Lake (PLTF,2010b); constructing a dam on the ridge andanother on Sullivan Creek would have been alogical approach to impound water.Existing Landforms and Geomorphic ProcessesThe following sections describe landforms andgeomorphic processes according to each lakeManagement Unit (Figure 3.1‐1). These unitswere largely defined by differences inlandforms and depositional patterns within thelake, as described in below.North Marsh and Sandbar West UnitsConstruction of the Phoenix Lake Dam createdcalm backwater conditions and a deltaicenvironment where the principal tributaries(i.e., Sullivan, Chicken and Power creeks) enterthe lake. The deltas of these tributariesoriginally formed near the margins of the lake.Over time, the deltas prograded into the lakeand coalesced to form the North Marsh. Figure3.1‐3 provides a conceptual cross‐section thatdepicts the history of sediment deposition inthe lake and formation of the North Marsh andthe current sandbar. The Sandbar West Unit isthe distal end of the delta, and the active zoneof deposition and delta extension (Figures 3.1‐2and 3.1‐2, Photo 3.1‐4).Photo 3.1‐4. The sandbar in Phoenix Lake is adepositional feature formed by sediment delivered fromSullivan, Chicken and Power creeks.Photo 3.1‐5 shows a photograph of astreambank taken near the mouth of ChickenCreek illustrating the process of sedimentationand subsequent formation of the North Marsh.Photo 3.1‐5. The streambank profile depicts a timesequence of sediment deposition and vegetation growthin the lake.As shown in Photo 3.1‐5, the bottom layer ofthe streambank is comprised of coarsersediment (i.e., sand and gravel) that wasdeposited soon after the dam was constructed.As the streambank grew in height, finersediment carried in Chicken Creek as suspendedload during higher streamflows was depositedoverbank on the floodplain. Coarse sediment3.1‐7


Chapter 3 – Part IPhoto 3.1‐7. The shallow depth of the Spillway Unit isevident in this photo taken during sediment samplingactivities conducted in April 2011.Ridge UnitThis unit encompasses an area of high groundwithin the lake that was flooded by theconstruction of the dam. The Ridge Unit isimportant in that its elevation influences watermixing, sedimentation patterns, and the usablestorage in the eastern portions of the lake. Thetopographic low point of the Ridge Unit islocated close to the dam‐side (southwest) ofthe unit. This location was likely the historicalconfluence between the eastern drainages andSullivan Creek.Sandbar East UnitThe Sandbar East Unit is part of the SullivanCreek delta, but is somewhat segregated fromthe main delta lobe (i.e., the Sandbar WestUnit) by the Ridge Unit. The Sandbar East Unitremains a depositional area, but in contrast tothe Sandbar West Unit, sediment deliveryappears to primarily be through suspended loadas opposed to bedload. This observation isbased on the finer grain sizes observed in thisunit.East Pool UnitThe East Pool is a broad, shallow portion of thelake. In the post‐dam condition the East Poolcontinues to receive sediment from theLake Preservation & Restoration ConceptsRidgewood and Phoenix Lake Park watersheds,but now also receives a portion of thesuspended sediment delivered from theprincipal tributaries (i.e., Sullivan, Chicken andPower creeks). While the mixing hydraulics ofthe lake has not been studied, analysis of thelandforms suggests that the eastern portion ofthe lake functions as a backwater area duringstorm events. In addition, the winter timeprevailing winds are from the northwest. Thewind “pushes” sediment‐laden water into thenortheastern portion of the lake; this effect isthought to be particularly significant tosedimentation dynamics in the Boot Unit.Boot UnitThe Boot Unit is a vegetated wetland that istopographically higher than the East Pool.Sedimentation in the Boot Unit is the result ofthe backwater and lake circulation‐induceddeposition processes described above, as wellas high sediment loads delivered from theRidgewood watershed. There are severalanecdotal accounts of high sediment deliveryand rapid marsh expansion associated withconstruction of the Ridgewood development inthe 1980s. Vegetated areas within the Boot Unitare very effective in trapping sedimentdelivered from the lake or watershed sources(Photo 3.1‐8).Photo 3.1‐8. Dense growth of bulrush in the Boot Unit.3.1‐10


Chapter 3 – Part I2.5 Biological ResourcesPhoenix Lake supports a mosaic of aquatic andwetland habitats that are surrounded byforested uplands and developed areas. Habitatsin and around the lake are described in thissection. No focused surveys for fish or wildlifewere conducted as part of this study, thusinformation presented in this section is basedon casual observations, existing information,and knowledge of similar sites in the region.Aquatic HabitatFigure 3.1‐4 depicts the biological zones thatoccur in a typical lacustrine system. The littoralzone in lakes is the area where there issufficient light penetration to support thegrowth of aquatic macrophytes. Nearly all ofPhoenix Lake functions as a littoral zone. Asmall portion of the total lake area functions asa limnetic zone (i.e., there is sufficient depth tolimit light penetration and growth ofmacrophytes).Lake Preservation & Restoration Conceptspenetration, though most plants are found inwaters to 10 ft in depth (Donaldson andJohnson, 2002).Photo 3.1‐9. Eurasian watermilfoil and hydrilla in PhoenixLake.Eurasian watermilfoil can degrade aquatichabitat by displacing native submerged aquaticvegetation. Watermilfoil also interferes withmunicipal and recreational uses of the lake.Control methods and management strategiesfor this species area discussed in Section 3.Figure 3.1‐4. Physical and biological lake zones(Lakeaccess.org, 2011).Most of the littoral zone in the lake has beeninvaded by Eurasian watermilfoil (watermilfoil,Myriophyllum spicatum) (Photo 3.1‐9). Thegrowth rates and spatial distribution of thisnonnative, invasive plant are mainly influencedby light availability, nutrient concentrations andtemperature. Watermilfoil tends to grow inwaters up to 20 ft deep, depending on light3.1‐11Other aquatic habitats in Phoenix Lake includerelatively narrow channels that intersectvegetated wetlands. These channels do notsupport growth of aquatic vegetation becausethe streambed is disturbed during storm events,which limits the ability of plants to establish inthese areas.Aquatic habitats in Phoenix Lake supportpopulations of warm water fishes such as bass(Micropterus sp.) and bluegill (Lepomismacrochirus). Native amphibians such as Pacificchorus frog (Pseudacris regilla) may breed inand along the margins of the lake. The lakeprovides suitable habitat for western pondturtle (Actinemys marmorata), which is a statespecies of concern. The lake’s aquatic habitat isalso used by numerous species of waterfowlsuch as American Coot (Fulica americana),


Chapter 3 – Part ILake Preservation & Restoration ConceptsMallard (Anas platyrhynchos), Canada Goose(Branta canadensis) and Graylag Goose (Anseranser) (Photo 3.1‐10). In addition, river otter(Lontra canadensis) may utilize the aquatichabitats in the lake (PLTF, 2010a)Photo 3.1‐11. Wet meadow (foreground) and riparian(background) habitats near the mouth of the Ridgewooddrainage.Photo 3.1‐10. Canada and Graylag Geese in Phoenix Lake.Wetland HabitatVegetated wetland habitats in Phoenix Lakeinclude the broad expanses of the North Marsh,the Boot, and “fringe” wetlands occurring alongthe margins of the lake. The vast majority ofwetlands in the lake are emergent wetlandsdominated by hardstem bulrush(Schoenoplectus [=Scirpus] acutus). Vegetationspecies diversity in the emergent wetlands islow.Near the historical mouth of Sullivan Creekcottonwoods (Populus fremontii) and willow(Salix spp.) grow on top of the creek bank withblackberry (Rubus spp.) in the understory.Similar riparian vegetation communities andwet meadow habitats occur at the mouths ofPower and Ridgewood drainages (Photo 3.1‐11). Wetlands fed by subsurface seepagedownstream of the Phoenix Lake Dam supportwhite alder (Alnus rhombifolia) in the overstoryand Himalayan blackberry (Rubus discolor) inthe understory.Vegetated wetland habitats are utilized by avariety of wildlife species. The vast expanses ofbulrush marsh provide nesting habitat for Red‐Winged Blackbird (Agelaius phoeniceus), MarshWren (Cistothorus palustris), and Sora (Porzanacarolina). There is a documented occurrence ofTricolored Blackbird (Agelaius tricolor), a statespecies of concern, in the North Marsh.Reptiles and amphibians described in theprevious section may also use wetlands asnesting, foraging, and dispersal habitat.When the lake level is low in the winter,unconsolidated shore wetlands are exposed inthe Sandbar Units, portions of the Ridge Unit,and a small island in the East Pool. These areasprovide foraging and loafing habitat forwaterfowl.Terrestrial HabitatThe lake is largely surrounded by landscapedresidences interspersed with native oaks(Quercus spp.) and pines (Pinus spp.). ThePhoenix Lake Dam face supports nonnativeannual grassland. The North Marsh is boundedby ponderosa pine (Pinus ponderosa) forest andriparian habitat associated with the principaltributaries.3.1‐12


Chapter 3 – Part ITerrestrial habitats surrounding the lakeprovide habitat for a variety of birds andmammals. Notable bird species that have beenobserved foraging around Phoenix Lake includeBald Eagle (Haliaeetus leucocephalus) andOsprey (Pandion haliaetus). Mammal speciesthat are likely to occur in the vicinity of the lakeinclude raccoon (Procyon lotor), black‐taileddeer (Odocoileus hemionus columbianus), andbat species.Lake Preservation & Restoration Conceptsquality parameters. Data collected were used toassess how well the lake can support thesebeneficial uses, and what measures can beimplemented to improve water qualityconditions. The findings of the water qualityassessment are presented in Chapter 4 of thePLPRP.2.6 Water QualityAddressing water quality in Phoenix Lake is akey component of the PLPRP as it affectspotable water supply, habitat functions, lakeaesthetics, and recreational opportunities. TheCentral Valley Regional Water Quality ControlBoard’s (RWQCB) Basin Plan (RWQCB, 2009)establishes beneficial uses for the UpperTuolumne watershed, which includes PhoenixLake. While developing the PLPRP is a planningprocess and not a regulatory‐driven process,the beneficial uses defined in the Basin Plan areuseful to establish context and identifyobjectives for water quality management inPhoenix Lake. Specific beneficial uses applicableto Phoenix Lake include:• Municipal and Domestic Supply (MUN)• Non‐water Contact Recreation (REC‐2)• Freshwater Habitat (WARM and COLD)• Wildlife Habitat (WILD)Protection of these Basin Plan beneficial uses isconsistent with the overall objectives of thePLPRP.The PLPRP included a water quality monitoringplan designed to describe current conditions inPhoenix Lake with respect to the objectives andthe beneficial uses listed above. The waterquality monitoring plan included continuousmonitoring of lake water temperature anddiscrete measurements of various lake water3.1‐13


Chapter 3 – Part I3.0 PRESERVATION &RESTORATION CONCEPTSThis section presents describes activities thataim to restore storage capacity, improve waterquality and aesthetics, and preserve or enhanceaquatic and wetland habitats in Phoenix Lake.The main preservation and restoration activitiesinclude sediment removal, sediment forebays,and wetland area enhancements. Collectively,these activities represent a conceptualapproach for improving and sustaining thelake’s water supply functions while enhancingecological conditions. This section continueswith detailed descriptions of these actions, aswell as proposed interim managementmeasures that can be implemented in thenearer term, prior to longer term and largeractions.3.1 Sediment RemovalPhysical sediment removal is the most directmethod to restore lake capacity in the nearterm. Sediment removal includes dredging andexcavation to restore storage capacity, improvewater quality and aquatic habitat, and enhanceaesthetics. Restoring depth in shallow portionsof the lake would improve water quality andaquatic habitat by expanding the limnetic zone,thereby reducing the area available to supportthe growth of invasive watermilfoil. Increasinglake depth would also decrease mean summerwater temperature, which would reduceeutrophication rates and potentially expandcold water habitat.Figure 3.1‐5 shows lake areas where sedimentremoval activities are proposed. Sedimentremoval in these areas would have limitedimpact to existing vegetated wetlands. Thesediment removal areas are offset from the lakeshoreline to allow for gradual transitions alongLake Preservation & Restoration Conceptsthe lake margins and to account for potentiallyshallow bedrock.Table 3.1‐2 provides estimates of sedimentremoval quantities and the resultant storagecapacity that would be restored by dredging orexcavating the lake to a range of depths. Forexample, dredging Sandbar West Unit to 10 ftbelow the existing surface would generateapproximately 35,000 cy of sediment andrestore 21.8 ac‐ft of storage.For conceptual design purposes, a target waterdepth of 8 ft at OWLL and 14 ft at OSLL wasselected for sediment removal activities (Table3.1‐2). This depth is equivalent to a lakebedelevation of approximately 2,370 ft above MSL.This target water depth is based on aquatichabitat objectives, lake bed morphology,estimated depth of sedimentation, andprofessional experience managing similaraquatic resources. Site observation suggeststhat restoring this lake depth wouldsubstantially limit the growth of watermilfoil,and improve water quality and aesthetics. Thistarget depth also appears to be within the zoneof sedimentation for all management units (i.e.,there would not be dredging or excavation intonative lakebed material).A discussion of proposed sediment removalactivities for each management unit follows.Sediment removal methods for eachmanagement unit also are described below.Table 3.1‐3 summarizes the sediment removalvolumes and the resultant increase in storagecapacity for the conceptual plan presentedbelow.3.1‐14


D EUSE OF DOCUMENTSTHIS DOCUMENT, INCLUDING THEINCORPORATED DESIGNS, IS ANINSTRUMENT OF SERVICE FORTHIS PROJECT AND SHALL NOT BEUSED FOR ANY OTHER PROJECTWITHOUT THE WRITTENAUTHORIZATION OF T.U.D.DOCUMENT RELEASEREV EWREV S ON NOTESDES GNEDSLDDRAWNSLDREV EWEDCTHAPPROVEDCTHPREPARED BYSONORA, CA 95370 (209) 532-553618885 NUGGET BLVD.TUOLUMNEUTILITIESDISTRICTPREPARED FORPROPOSED LAKE MANAGEMENT CONCEPTSPHOENIX LAKEPRESERVATION ANDRESTORATION PLANSONORA CAL FORN ALEGENDSEDIMENT MANAGEMENT ANDWETLAND ENHANCEMENTSEDIMENT REMOVAL AREAMATERIALS HANDLING AREA23802375238023802375752375 37523N0 200' 400' 800'2370 2375238023802375375 752380237002375237523802370237523701234A B CFILE NAMEMgt Units.dwgJOB NUMBER10-1019DATEJune, 2011FIGURE3.1-5


Table 3.1‐2: Conceptual‐level Estimates of Sediment Removal Quantities and Resultant Storage Capacity RestorationManagement Unit and Sediment Removal AreasSpillway West Pool Sandbar West Ridge Sandbar East East Pool TotalTotal Area (acres) 5.38 5.78 2.18 5.72 2.38 32.00 53.43Total Area (ft 2 ) 234,296 251,663 95,047 249,334 103,494 1,393,793 2,327,627Sediment Removal Area*(ft 2 ) 159,214 179,057 95,047 54,237 103,494 857,726 1,448,775Depth of SedimentVolume of Sediment Removed by Depth (CY) ‐ (Volumes are cumulative, to depth shown)Removal below ExistingSurface Elevation (ft) Spillway** West Pool Sandbar West Ridge Sandbar East East Pool Total1 5,897 6,632 3,520 402 3,833 31,768 52,0512 11,794 13,263 7,041 4,018 7,666 63,535 107,3173 17,690 19,895 10,561 6,026 11,499 95,303 160,9754 23,587 26,527 14,081 8,035 15,332 127,071 214,6335 29,484 33,159 17,601 10,044 19,166 158,838 268,2926 35,381 39,790 21,122 12,053 22,999 190,606 321,9507 41,278 46,422 24,642 14,061 26,832 222,373 375,6088 47,175 53,054 28,162 16,070 30,665 254,141 429,2679 53,071 59,686 31,682 18,079 34,498 285,909 482,92510 58,968 66,317 35,203 20,088 38,331 317,676 536,583Total of proposed sediment removal depths (blue cells) 232,461Depth of SedimentCapacity Restored by Depth (ac‐ft) (Volumes are cumulative, to depth shown)Removal below ExistingSurface Elevation (ft) Spillway West Pool Sandbar West Ridge Sandbar East East Pool Total1 3.7 4.1 2.2 0.2 2.4 19.7 322 7.3 8.2 4.4 0.5 4.8 39.4 653 11.0 12.3 6.5 0.7 7.1 59.1 974 14.6 16.4 8.7 1.0 9.5 78.8 1295 18.3 20.6 10.9 1.2 11.9 98.5 1616 21.9 24.7 13.1 1.5 14.3 118.2 1947 25.6 28.8 15.3 1.7 16.6 137.9 2268 29.2 32.9 17.5 2.0 19.0 157.6 2589 32.9 37.0 19.6 2.2 21.4 177.3 29010 36.6 41.1 21.8 2.5 23.8 196.9 323Total capacity restored for concept plan (blue cells) 139


Table 3.1‐2: Conceptual‐level Estimates of Sediment Removal Quantities and Resultant Storage Capacity RestorationNOTES:* Explanation of Sediment Removal Areas:Management UnitSpillwayWest PoolSandbar WestRidgeSandbar EastEast PoolCalculation AreaSediment removal area does not include the portion of the unit west of the TUD pipeline crossing due to potential access constraints.The majority of the calculation area is flat. Calculation of estimated sediment removal volume was taken over the calculation area(Figure 3‐1) to the depths indicated.The sediment removal area avoids dredging: (1) existing deep area in the vicinity of the intake tower; (2) competent material the midlakeRidge; and (3) along the shoreline. Estimated dredging volume was taken over the calculation area to the depths indicated.This management unit is generally flat with average elevation of 2380 ft. Estimated excavation volume calculations were made over theentire area.The calculation area includes a mounded, sloping area of sediment aggradation. Volume estimates were roughly estimated over thecalculation area to the depths shown, in order to meet the Winter storage depth goal. Additional excavation may be included toincrease connectivity between East and West pools, but it is not included in this estimate.Volume estimate was taken over the area of the management unit to a depth of 4'.The sediment removal area avoids dredging along the shoreline and an existing island that provides winter time bird resting/loafinghabitat. Estimated dredging volume was taken over the calculation area to the depths indicated.** Highlighted cells indicate proposed sediment removal depths for conceptual plan


Table 3.1‐3: Sediment Quantities and Storage Capacity Restoration associated with Proposed Sediment Removal ActivitiesManagement UnitSpillway West Pool 1 Sandbar West Ridge 1 Sandbar East East Pool Total 1Total Area (acres) 5.38 5.78 2.18 5.72 2.38 32.00 53.43Total Area (ft 2 ) 234,296 251,663 95,047 249,334 103,494 1,393,793 2,327,627Sediment Removal Area(ft 2 ) 159,214 209,267 95,047 122,610 103,494 857,726 1,547,358Proposed Depth ofSediment Removal belowExisting Surface Elevation(ft) 6 2 10 5 3 4 NAResultant Mean WaterDepth at OWLL (ft) 8 10 8 varies 4 8 NAVolume of SedimentRemoved (CY) 35,381 19,977 35,203 35,367 11,499 127,071 264,497Storage Capacity Restored(ac‐ft) 21.9 12.4 21.8 21.9 7.1 78.8 164.0Notes:1. Total sediment removal and storage capacity restored is greater than values presented in Table 3‐2 because calculation for the West Pool includedredging a channel connecting to the 1986 dredge hole (6,713 cy), and calculations for the Ridge Unit include dredging/excavation of the East‐West Poolconnector channel (25, 323 cy)


Chapter 3 – Part ILake Preservation & Restoration ConceptsSpillway UnitThe existing water depth in this unit isapproximately 2 ft at OWLL. Removingapproximately 6 ft of sediment would achievethe target lake depth. Sediment removal in thisunit may be accomplished through acombination of lake‐based dredging and landbasedexcavation equipment operatingprimarily from the dam. The TUD pipeline whichcrosses this unit may restrict access forsediment removal in the portion of the unit thatis closest to the spillway. For this reason,sediment removal estimates exclude this area(Figure 3.1‐5, Tables 3.1‐2 and 3.1‐3).West Pool UnitMost of this unit already meets or exceeds thetarget water depths. Additional sedimentremoval of approximately 2 ft is proposed asmaintenance dredging to restore lake storagecapacity. Sediment removal in this unit wouldrequire dredging; land based excavation is notlikely feasible.Sandbar West UnitThis unit is currently 1‐2 ft above OWLL (Figure3.1‐1). Removal of approximately 10 ft ofsediment would achieve the target depth forwater quality improvement. Sediment removalin this unit may be accomplished withconventional land‐based excavation equipmentoperating during low water periods. Access forsediment removal could be accomplished byconstructing temporary roads connecting toLakeview Drive or by operating small barges onthe lake to move material to another accesspoint. Sediment removed from the SandbarWest Unit is anticipated to be predominatelysand and gravel; this material may be suitablefor construction aggregate and landscapingpurposes. Further development of sedimentremoval plans will need to consider appropriatetransition slopes between the excavation areasin this unit and existing wetlands in the NorthMarsh so as not to cause erosion.Ridge UnitSediment removal is proposed in thenorthwestern portion of the unit that iscontiguous with the West Pool. This portion ofthe Ridge Unit contains depositional materialfrom Sullivan Creek. Additionally, dredging of achannel to connect the East and West Pools isproposed in the southern portion of the unit(Figure 3.1‐5). This channel would improveconnectivity between the East and West Poolsand reduce the unusable storage volume in theEast Pool. Sediment removal methods for thisunit would likely be similar to methodsdescribed for the West Pool.Sandbar East UnitA shallow excavation depth (approximately 3 ft)is proposed in this unit because it believed thatthere is competent, native material near thesurface. Removal of native, non‐alluvial materialis not recommended because it is likely moreresistant to excavation than recently depositedalluvial sediments. Furthermore, removal ofnative, non‐alluvial material may be consideredby regulatory agencies as a reservoir“improvement” rather than maintenance ofstorage capacity. Sediment removal in this unitwould likely be accomplished with conventionalland‐based excavation equipment similar tothat described for the Sandbar West Unit.East Pool UnitThe existing water depth in this unit averagesapproximately 4 ft at OWLL. Removingapproximately 4 ft of sediment would achievethe target depth for water qualityimprovement. Sediment removal in this unitcould be accomplished with low‐draft dredgingequipment. Alternatively, if the lake level isdrawn down for a sufficient period of time, thensediment removal may be feasible with low3.1‐19


Chapter 3 – Part Iground pressure excavation equipmentoperating on construction mats. The PLTFDredging report (PLTF, 2010a) presented the“two lake” concept, which would utilize themid‐lake ridge to divide the lake for dewatering.This concept has merit and should continue tobe evaluated as a potential method forsediment removal in the East Pool.Construction AccessFigure 3.1‐5 shows locations that are potentiallysuitable access points for sediment removaloperations. Potential access points includeexisting roads at Phoenix Lake Park, PhoenixLake Dam and Apple Valley Estates, and newroads connecting the lake to Lakeview Drive andMeadowbrook Drive. It is important to notethat the suitability of these access points isbased mainly on physical conditions; privatelandowners and homeowner associations havenot agreed to accommodate constructionaccess.Access through Phoenix Lake Park via Lori Laneis an existing lake access point that could beused to launch dredging equipment and removesediment. In the current condition this locationmay be too shallow to launch conventionalsuction dredge equipment; low draft dredgingequipment (Photo 3.1‐12) may be needed alongwith site improvements to launch equipment.Lake Preservation & Restoration ConceptsThis location also provides the most convenientconnection to Phoenix Lake Road, which willlikely be an important route if sediment needsto be moved by truck to disposal areas.Access through the TUD easement to the damwould allow for land‐based sediment removalfrom the dam. Improvements could be made atthe dam which may allow for the launching ofsuction dredge equipment. However, the accessmay be constrained by clearance on the roadleading to the dam. Specialized equipment,such as modular barges (Photo 3.1‐13), may beuseful for launching equipment at this location.Photo 3.1‐13. A modular barge provides a platform forexcavation equipment (courtesy of flexifloat.com).The existing boat ramp in Apple Valley Estates isanother potential location for constructionaccess (Figure 3.1‐5). There have been somediscussions with the homeowner associationand they have indicated they may be amenableto use of the boat ramp, but some homeownershave expressed reservations about a highvolume of construction traffic (PLTF, 2010a).Photo 3.1‐12. Example of a small, low draft suctiondredge.3.1‐20Establishing access via Meadowbrook Drivewould require construction of a new road


Chapter 3 – Part Iconnecting to the dam. The TUD owns propertyin this location, but may need to acquireadditional property or easements to construct anew road. Establishing access at this location isdesirable because the new road could bedesigned to accommodate a range of dredgingand hauling equipment. Additionally, the newroad could be used for long‐term access andmaintenance.It may be desirable to establish temporaryaccess via property located on Lakeview Drive(Figure 3.1‐5). Access at this location wouldallow for a land‐based route for sedimentremoval in the Sandbar East and West Units.This access would likely include temporarygravel roads that could be removed andrevegetated once sediment removal iscompleted.Materials HandlingMaterials handling includes the necessaryprocedures to prepare sediment for beneficialreuse or disposal. The materials handlingprocedures will vary based on sedimentmoisture content, texture, removal location andexcavation methods. The moisture content ofcoarse material (sand and gravel) moved withconventional excavation equipment may be lowenough to load directly into trucks for haulingto a reuse or disposal area. Sediment removedwith suction dredge equipment will have highwater content (typically 80% water) and willneed to be dewatered in a materials handlingfacility.Figure 3.1‐5 shows proposed materials handingareas located within and around the lake. Atemporary dredged materials handling area isproposed in the southeast portion of the lake toserve as a sediment drying and transfer point. Atemporary levee or berm would be constructedin the lake to create the sediment drying area.Sediment pumped to this area with a suctionLake Preservation & Restoration Conceptsdredge would settle and excess water would bedecanted back into the lake. Sediment would bedried until it reaches a moisture content that issuitable for transport to a permanent disposalarea.The land‐side of the dam is another potentiallocation for dredged materials handling.Sediment may be placed at this location with along‐reach excavator or clamshell dredgeoperating from the dam or pumped directly tothis area with suction dredge equipment. If thisarea is used to handle sediment delivereddirectly from a suction dredge operating in thelake, then substantial site modifications wouldbe required including construction containmentberms or levees and a dewatering system.Finally, the area that was used in 1986 fordredged materials handling (Figure 3.1‐5) isanother potential option, though the landownerhas not been contacted to gage interest orwillingness to use the land for this purpose.Beneficial Reuse and DisposalSediment texture and quality are importantfactors for evaluating potential reuse anddisposal options. Coarse material removed fromthe Sandbar West Unit is potentially suitable forconstruction aggregate and landscapingpurposes. Fine sediment (clay and silt) is wellsuitedfor agricultural, wetlands restoration andsome landscaping uses. The owner of the appleorchards adjacent to the lake has expressedinterest in reusing sediment. Hauling sedimentfor reuse in Central Valley agriculturaloperations may also be feasible, but is likely toprove more costly than local reuse or disposaloptions. Other potential beneficial reuseoptions include a quarry restoration at theJamestown Mine and a California Departmentof Fish and Game wetlands restoration site onthe Merced River near Snelling, CA. Again, costis likely to be the deciding factor, with on‐site or3.1‐21


Chapter 3 – Part Ilocal disposal likely to be the most costeffectiveoption. Grant funding is more likely tobe available for beneficial reuse of sedimentthat involves habitat restoration such as TUD’sSierra Pines property near Twain Harte.Sediment that cannot be reused will need to bedisposed of. Figure 3.1‐5 and Photo 3.1‐14show an on‐site stockpile and disposal area onthe land‐side of the dam.Photo 3.1‐14. Potential sediment stockpile and disposalarea on the land‐side of Phoenix Lake Dam.It is anticipated that placing material at thislocation would be the most cost effectivedisposal option because TUD owns the propertyand placing material at this location wouldrequire minimal transportation time. The siteshown in Photo 3.1‐14 has been alteredpreviously for past lake dredging andmanagement actions. The site’s proposed usenow for sediment storage and disposalpurposes is consistent with past land uses of thesite. Sediment removed from the lake withexcavation equipment operating on the dammay be able to place material directly in thisarea. It is unlikely that material removed fromthe lake with suction dredge equipment wouldbe able to placed directly at this locationbecause the water content and volume ofdecant water would be too high. The dredgedmaterial would first need to be dried in aLake Preservation & Restoration Conceptsmaterials handling area, such as the location inthe southeastern portion of the lake (Figure 3.1‐5), and then moved to this location. This wouldrequire the material to be moved via the roadon the dam or a new road to MeadowbrookDrive. Sediment removed from the lake couldalso be used to build the new road connectingto Meadowbrook Lane. The extents of thisdisposal area and the volume of material thatcan be placed at this location are underinvestigation.Sediment samples were collected from severallocations in the lake to test the material forcontamination and suitability for reuse and landapplications. Preliminary screening suggeststhat sediment in the lake does not containhazardous levels of contaminants of concernand that the material may suitable for a broadrange of reuse applications. (See Chapter 4 ofthe PLPRP for a more detailed assessment ofthe suitability of sediment for reuse anddisposal).3.2 Sediment ForebaysIn contrast to removing sediment directly fromthe lake, the sediment forebay approach usesbasins located just upstream of the lake toefficiently trap sediment prior to it entering thelake. From these forebay locations, the trappedsediment can then be removed and disposed.In the right locations, sediment forebay typebasins provide an effective sediment reducingmethod. Used in combination with direct lakesediment removal, sediment forebays alsoprovide sediment reducing benefits for themedium and longer‐term timeframe. Thissection describes the use of sediment forebaysto help achieve longer‐term sustainability oflake functions.3.1‐22


Chapter 3 – Part ILake Preservation & Restoration ConceptsSullivan Creek Sediment ForebayAs mentioned in Section 2.4, the delta ofSullivan, Power and Chicken creeks hasprogressed into the center of the lake. Thisresults in coarse sediment loads depositing inopen water portions of the lake and gradualencroachment of wetlands. Use of a sedimenttrapping forebay upstream of this location canreduce the sediment loading and the rate ofdeltaic progression.The sediment forebay functions by creatingquiescent conditions where sediment candeposit before moving into the lake. Creatingan impoundment and backwater conditionsreduces flow velocity, slope and turbulencewhich will allow for the deposition of sediment.Deposited sediments can then be removedthrough a regular maintenance program usingland‐based excavation equipment rather thanmore costly subaqueous dredging. One of thekey advantages of a sediment forebay is itsknown/defined location in terms of access andrepeat maintenance operations.A general sediment forebay design for SullivanCreek includes three components: 1) a watercontrol structure across the existing SullivanCreek channel, 2) the sediment forebay, and 3)an outlet structure and overflow weir (Figure3.1‐6). The purpose of the water controlstructure across the existing Sullivan Creekchannel is to divert water and sediment into theforebay. The water control structure is notintended to provide a permanent blockage toflows down the existing Sullivan Creek channel.Rather, it would be used to divert waterthrough the sediment forebay during periods ofelevated discharge and sediment transport.During periods when discharge and sedimenttransport levels are low, the water controlstructure could be opened allowing a bypassand drawdown of the sediment forebay toallow trapped sediments to drain and dry prior3.1‐23to handling and removal. The control structurecould include a mechanically operated sluicegate, or alternatively could consist of multiplebays with manually removable boards.As presented at this conceptual level, theSullivan Creek sediment forebay is 1.5 acres insize, and 3 ft deep prior to the deposition of anysediment, resulting in an impounded volume ofapproximately 4.5 ac‐ft. The existing groundsurface elevation in the footprint of thesedimentation forebay is approximately 2,385 ftat the downstream extent, rising toapproximately 2,387 ft at the upstream extent.Two conceptual design options have beenconsidered. Typical cross‐sections for theseoptions are shown on Figure 3.1‐7.Option 1 sets the base elevation of thesediment forebay at 2,385 ft, which is equal tothe OSLL. With this bottom elevation trappedsediments would sit above the summer waterlevel and dry more readily, allowing for lesscostly removal during the summer monthswhen the lake water surface elevation is at2,385 ft. As conceptually designed, the watersurface elevation in the forebay would be 2,388ft, and the sediment forebay would becontained by a berm with a top elevation of2,389 ft (allowing for 0.5‐1 ft of freeboard). Bysetting the bottom of the sediment forebay ator above OSLL, a backwater would extendupstream along Sullivan Creek from theforebay. This backwater could increase floodingin the lower reach of Sullivan Creek, and couldalso promote deposition of coarse sediment inthe creek channel, rather than in the sedimentforebay, leading to more challengingmaintenance and removal. In order to addressthese concerns, a second option is considered.


℄℄ ℄ ℄℄℄


Chapter 3 – Part IOption 2, has the same footprint (1.5 acres) andoperational depth (3 ft) as option 1, however ithas a lower base elevation of 2,381 ft toaddress the backwatering issue anticipated forOption 1. With a lower base elevation, Option 2would reduce the upstream extent of thebackwater created by the sediment forebay.This would reduce the potential for floodingupstream, as well as reduce the amount ofsediment deposited in the Sullivan Creekchannel before entering the forebay. Thisoption would present increased excavationcosts at the time of construction, but reducedcosts regarding the construction of thecontainment berm. One disadvantage of thisoption is in regard to the removal and handlingof the trapped sediments. Since the baseelevation of the sediment forebay is belowOSLL, sediments will likely be saturated duringthe summer months, leading to more complexmaintenance. However, if sediment could beremoved on the shoulders of the wet season,either before (e.g., April) or after(October/November) the period when the lakesurface is at 2,385 ft, then this option is perhapspreferable. This option may also require theconstruction of an inlet control structure toprevent creek water from entering thesediment forebay during times when forebaybypass is desired.Either sediment forebay option will require theconstruction of an outlet control structure andoverflow spillway. The outlet control structurewould control the water surface elevation in theforebay, but also allow for complete drainage ofthe forebay for sediment drying andmaintenance. As conceptualized, this wouldinclude a top down, bottom up sluice gate;however other options are available and shouldbe explored if this sediment managementconcept is prioritized. In addition to outletcontrol, an overflow spillway is required toLake Preservation & Restoration Conceptsallow for the controlled passage of high floodflows. As conceptualized, an overflow weir isincluded in the containment berm flowing tothe constructed channel through the marshdownstream.Alternatives to the two options presentedinclude a change in size of the forebay by eitherincreasing its footprint or depth. As presented,the forebay is 1.5 acres; however more room isavailable at the proposed location to increasethe spatial extent. As presented, the maximumoperational depth of the forebay is 3 ft, prior tothe deposition of sediment. This is theminimum depth that should be considered,however, the depth could be increased to 5 ftto increase the volume of the forebay. Depthsexceeding 5 ft provide the need for moreelaborate design of the containment berms toensure public safety, however this is less of aconcern in Option 2, as berm heights are lower.Figure 3.1‐6 shows a potential construction andmaintenance access point for the sedimentforebay. Construction and maintenanceequipment could enter from the orchards onthe north side of the lake, then cross SullivanCreek to access the forebay area. The crest ofthe water control structure on Sullivan Creekwould provide the access route formaintenance of the sediment forebay. Theberm on the forebay would be designed toaccommodate light excavation and haulingequipment for sediment removal.Constructing the forebay at this location wouldrequire TUD to obtain property and/oreasements for construction and maintenance.The owner of the orchard property hasindicated that they may be amendable toestablishing a maintenance easement.Advancing the design of the sediment forebaywould require the development of a hydraulic3.1‐26


Chapter 3 – Part Imodel to determine backwater effects of theproposed designs. Sediment transport samplingwould provide valuable information towardsthe design and maintenance requirements.Additional engineering design would berequired for all components of the watercontrol structure and sediment forebay.Topographic surveys would be required for eachof these components, and geotechnicalinvestigations would be required for allcomponents.Boot Unit Sediment ForebayObservations of stormwater flows have notedhigh sediment loads entering the lake from theRidgewood drainage (PLTF, 2010d). A sedimentforebay similar to the one detailed for SullivanCreek may be considered in the Boot Unit totrap sediment entering the lake from theRidgewood drainage. A conceptual footprint fora sediment forebay in the Boot Unit is shown inFigure 3.1‐5. Conceptual designs for thissediment forebay have not been developed atthis stage, but may be advanced and evaluatedin subsequent phases of the PLPRP.3.3 Floodplain & Wetland AreaEnhancementsThe wetland enhancements proposed in thisconceptual plan aim to promote sedimentdeposition in marsh areas by restoringgeomorphic function to the creek channels andadjacent floodplains. The proposedenhancements include a new alignment ofSullivan Creek downstream of the sedimentforebay outlet, and floodplain benches alongthe principal creek channels (Figure 3.1‐6).A new alignment of Sullivan Creek would berequired to connect the sediment forebayoutlet with the existing Sullivan Creek channel.This affords an opportunity to construct achannel with appropriate geomorphic form andLake Preservation & Restoration Conceptsfunction. As mentioned previously, in theexisting condition the creek channels arerelatively straight, and isolated from theadjacent marsh surface due to the high banks ofthe channel. This limits the ability of theadjacent marsh plain to trap sediment. Theproposed meandering channel for SullivanCreek and floodplain benches would provide ahigher level of connectivity between thechannels and the floodplain such that asdischarge levels exceed the channel’s capacity,sediment‐laden water would flow onto thefloodplains. As flows spread out, and interactwith vegetation growing on the floodplain,velocities would be reduced and finersediments would be deposited prior to reachingthe usable storage zones of the lake.Floodplain benches are also proposed for thePower and Chicken creek channels to trap someportion of the fine sediment delivered fromthese drainages (Figure 3.1‐6 and 3.1‐7). Inaddition to improving sediment trapping, thenew floodplains would provide temporaryfirebreaks in the marsh. Over time, thefloodplain benches would increase in elevationand vegetation would become established. Thefloodplain surfaces and vegetation could bemaintained at a prescribed elevation tomaximize sediment trapping and firebreakfunctions.Figure 3.1‐7 shows a potential constructionaccess point for the new channel constructionand excavation of floodplain benches.Construction equipment could enter from theorchards on the north side of the lake. Most ofthe sediment excavated to create the newchannel and floodplain benches would need tobe removed from the lake. Some material maybe placed into existing marsh areas to providetopographic relief, which would increasehabitat diversity.3.1‐27


Chapter 3 – Part ILake Preservation & Restoration ConceptsEstablishing access at this location wouldrequire TUD to obtain an easement on privateproperty for construction access. The propertyowner has indicated that they may beamendable to establishing a construction andmaintenance easement and potentially longtermpublic access at this location. Public accessimprovements at this location could includepicnicking facilities, as well as a boardwalk andfishing pier extending into the lake. Establishingpublic access at this location would provide anexcellent educational opportunity with respectto the wetland ecology, sediment management,and water resources. (See Chapter 5 of thePLPRP for a more detailed discussion of publicaccess at this location).Other Wetland Enhancement OptionsOther wetland enhancement optionsconsidered for the North Marsh includecomplete “open water restoration” and the“Channels and Islands” approach recommendedby the PLTF (PLTF, 2010c). Complete openwater restoration would involve dredging theentire North Marsh to restore open water (i.e.,a lake environment). The Channels and Islandsapproach to wetland management involvesexcavating a network of channels within marshareas to improve water circulation, expand“edge” habitat and provide fire breaks (PLTF,2010c).Table 3.1‐4 provides a comparison of thevarious enhancement options considered forthe North Marsh. The comparison tableevaluates construction costs, storage capacityrestored, and probable environmental impacts.The open water restoration option would havethe highest cost and environmental impactsbecause it would remove the largest volume ofsediment and wetland area. However, thisoption would also restore the greatest volumeof storage capacity in the lake. The consultantteam chose not to advance this option as the3.1‐28preferred approach because of the high costand environment impacts relative to otheroptions.The Channels and Islands option has moderatecost and environmental impact relative to theother options considered (Table 3.1‐4). Thisapproach has merit with respect to habitatvalues and fire management (i.e., the channelswould create fuel breaks), but may beproblematic in terms of water quality. Thiswould be particularly true for the proposedperimeter channel around the lake. Theperimeter channel would likely have poorcirculation, particularly in the summer monthswhen the lake level is high. This would lead tostagnant water along the lake margins whichmay produce odors, suffer from low dissolvedoxygen concentrations, and provide mosquitobreeding habitat.The concept presented in this chapter (i.e., thePLPRP Concept Plan) was advanced in favor ofopen water restoration and the Channels andIslands approach for several reasons. First, thewetland enhancement concepts presented inthis chapter is the most effective means topromote or restore physical processes that willmaintain water quality, storage capacity andwetland functions in the lake. This option wasalso viewed as being the most practicalapproach from a cost and environmental impactstandpoint. Furthermore, the consultant teamhad concerns about the predictability ofsedimentation patterns with the Channels andIslands approach.In subsequent phases of design aspects of thechannels and islands approach could beintegrated into the wetland enhancementconcepts presented in this chapter. Ofparticular value would be creating islands thatare topographically lower and higher than theexisting marsh plain. Topographically low areas


Table 3.1‐4: Evaluation of North Marsh Restoration and Enhancement Options.OptionDescriptionApprox. Volume of Approx. CapacityApprox.TotalCapacityRestored OverLoss of EmergentWetlandTotal Cost for North Marsh UnitRestoration/Sediment Removed Restored Entire LakeProbable Construction Cost Probable Mitigation CostEnhancement(CY) (ac‐ft) (ac‐ft) (ac) Low High Low High Low HighProbable Environmental Impacts & PermittingConsiderationsOpen Water RestorationRestore open water in theNorth Marsh by dredgingthe entire area to 8 feetdeep at Ordinary WinterLake Level (OWLL, 2,379')531,028 329 493 28.0 $6,372,337 $10,620,561 $280,156 $840,468 $6,652,493 $11,461,030High. Much of the wetland habitat would be removed. Focusedwildlife surveys have not been conducted, so impacts to specialstatus species cannot be fully assessed.Channels & IslandsCreate wetland islands in anopen water matrix.Assumes a 1:1 ratio ofChannels (open water) toIslands (emergentwetlands).277,759 172 336 11.9 $3,333,103 $5,555,172 $0 $357,000 $3,333,103 $5,912,172Low to Moderate. This option restores a balance between openwater and emergent marsh habitats. With respect to the existingcondition, this would favor waterfowl over marsh dependentpasserines. Further consultation with resource agencies is neededto identify wildlife management priorities. Focused wildlife surveyshave not been conducted, so impacts to special status speciescannot be fully assessed.PLPRP Concept PlanExcavate new SullivanCreek alignment withexpanded floodplain.Expand floodplain ofChicken and Power creeks.53,600 33 197 11.1 $804,000 $1,340,000 $0 $333,000 $804,000 $1,673,000Low. This option includes similar habitat tradeoffs to the Channels &Islands option. Waterfowl resting/loafing habitat would be expandedon the floodplains. This option also includes water quality benefits oftrapping sediment on new floodplains. This option was favored inthe development of the 2011 Draft Plan because it works with thedominant fluvial process operating in the lake. Therefore, the designrationale for this option is well supported, which increases thelikelihood that the project will be viewed favorably by resourcemanagement agencies and grant funding entities.Assumptions and Explanation of Calculations:Open Water RestorationThe North Marsh Unit isapproximately 32.2 acres withapproximately 28 acres of wetlandsand 4.2 acres of channels. Assumean average marsh elevation of2,383' is dredged to 2371'(Difference of 12') to create 8' depthat OWLL. Channels at averageelevation of 2,378' are dredged to2371' (Difference of 7'). A 10%reduction in the total dredgingvolume is factored in to account forthe transition slopes on the lakemargins. Assume 1,613 cubic yardsof material in 1 acre‐foot.Assume dredging of1,613 cubic yards ofmaterial yields 1 acrefootof storage.North Marsh area that iscurrently emergentmarshAssumes a 1:1.1mitigation ratio fortemporary loss of wetlandfunctions.Channels & IslandsThe North Marsh Unit isapproximately 32.2 acres withapproximately 28 acres of wetlandsand 4.2 acres of channels. Assume11.9 acres of marsh at average1:1 ratio of emergent marsh (islands)elevation of 2,383' is dredged toto open water (channels) is favorable2371' (Difference of 12') to createfor many species of wetland wildlifechannels with 8' depth at OWLL.(Weller 1975, Kaminski and Price 1981,Assume 4.2 acres of channels atMurkin et al. 1982, Ball 1989) as citedaverage elevation of 2,378' isin Ball 1990.dredged to 2371' (Difference of 7')to create channels with 8' depth atOWLL. This would yield 16.1 acresof channels and 16.1 acres ofwetland remain.Assume dredging of1,613 cubic yards ofmaterial yields 1 acrefootof storage.North Marsh storagerestoration plus 164 ac‐ftin other managementunitsLoss of EmergentWetlandLow construction High constructionestimate of $15 per cy for estimate of $25 perdredging and disposal. cy for dredging andAssumes disposal. Assumesmobilization/demob are mobilization/demobincluded in larger lake are included in largerproject.lake project.Assumes that enhancedwetland functions andvalues obviates mitigationAssumes a 1:1.2mitigation ratio fortemporary loss ofwetland functions.Assume mitigation costper acre is$150,000/ac.Sum of low rangeestimatesSum of high rangeestimatesPLPRP Concept PlanCreate depositional floodplains to trapand store fine sediment in marsh areasto improve water quality indownstream open water areas.Includes dredging of new SullivanCreek channel and floodplainbenches on Sullivan, Chicken, andPower creeks.Assume dredging of1,613 cubic yards ofmaterial yields 1 acrefootof storage.Loss of EmergentWetlandAssumes that enhancedwetland functions andvalues obviates mitigation


Chapter 3 – Part Iwould provide winter time resting/loafinghabitat for waterfowl. Creating topographicallyhigher areas would increase vegetationstructure and diversity by providing suitableareas for willow and cottonwood growth. Overtime, this woody vegetation would provideroosting and nesting habitat for a diverse rangebird species.3.4 Cost Estimates & PhasingConceptual Cost EstimatesTables 3.1‐5a and 3.1‐5b provide conceptuallevel cost estimates for implementing theactivities described in the previous sections. Thecost estimates do not include inflation or longtermmaintenance of the sediment forebay(s)or floodplains in the marsh areas.PhasingSeveral factors may influence the schedule forplanning and implementing sedimentmanagement activities. The factors most likelyto influence project schedule are funding,environmental permitting, and land acquisitionor access agreements. Construction methodsmay also influence the phasing of the project,particularly if there is a limited area fordewatering and sediment drying to occur.Moreover, construction windows are likely tobe constrained by biological concerns (e.g., birdnesting seasons) and lake levels (i.e., tooshallow or too deep to operate equipment).Lake Preservation & Restoration Conceptslarge‐scale lake dredging so that the lake wouldnot refill with sediment soon after dredging.This is prudent advice and should be consideredwhen planning the phasing of lake preservationand restoration activities. However, waterquality and aesthetics concerns in Phoenix Lakewarrant timely intervention. The followingsection discusses interim managementmeasures that can help address these issueswhile large‐scale sediment removal andsediment management activities can beplanned and implemented.3.5 Other Lake Management MeasuresAquatic Vegetation Harvesting and AlgaeRemovalAs mentioned in Section 2.5, much of the lakesupports a dense growth of submerged aquaticvegetation including Eurasian watermilfoil andhydrilla. The removal of the accumulatedvegetation biomass would minimize seasonalalgal blooms and improve water quality andaesthetics. Aquatic vegetation sequestersnutrients accumulated from sediment andwater column. When the plants die offseasonally they release nutrients back into thewater, which are absorbed by algae. Harvestingvegetation will eliminate the bulk of thebiomass, leaving the lake in an aestheticallypleasing condition, as well as slowing down theeutrophication process.Most of the activities described above could beimplemented as standalone projects within thelarger PLPRP. However, it is important torecognize that costs for mobilization anddemobilization for several small projects will besubstantially higher than for a single, largeproject. This is particularly true for projects thatinvolve water‐based dredging equipment.Finally, the PLTF recommends having sedimentbasins (or forebays) in place prior to conducting3.1‐30The PLTF has clearly stated opposition to usingchemical treatments (i.e., herbicides) to treatinfestation of aquatic vegetation, However, theTUD has not addressed this issue and at thistime is neutral on using chemical treatments.To perform mechanical maintenance, a largeharvester could be employed with local disposaloptions (e.g., on the land‐side of the dam).Given the size and density of infestation(estimated at 25‐30 acres), harvesting would


Table 3.1‐5a: Conceptual Level Opinion of Probable Cost for Select Components of the Phoenix Lake Preservation and Restoration Plan.Item No. Description Qty Units $/Unit Total Notes and AssumptionsA. ACQUISITIONS, ENGINEERING, ENVIRONMENTAL COMPLIANCE, ADMINISTRATIONA‐1 Land Acquisition for Sediment Forebay 3 Ac $31,500.00 $94,500 LandandFarm.com average cost/acre in SonoraA‐2 Access and Easement Purchases TBD TBD TBD 0 To be DeterminedA‐3Engineering ‐ Sediment Removal, Forebays, Outlet Structures,and Channels 1 LS $250,000A‐4 Environmental Compliance and Permitting 1 LS $300,000A‐5 TUD Project Administration 1 LS $352,156 5% of construction costsSubtotal ‐ Acquisitions, E&E, Admin $996,656Horizon/cbec estimate. Assumes 60%, 90%, 100% plans and SWPPP. Otherengineering analyses such as geotechnical investigation and sedimenttransport modeling not included.Horizon/cbec estimate. Assumes CEQA compliance, USACE 404 permit,RWQCB 401 Certification and WDR, CDFG 1602 Stream and Lake BedAlteration Agreement, ESA/CESA compliance.B. GENERAL CONSTRUCTION REQUIREMENTSB‐1 Mobilization/Demobilization 1 LS $140,862 2% of job cost. Assumes single mobilization/eventB‐2 Construction Surveying 24 hr $230.00 $5,520 2‐man crew, Construction StakingSubtotal ‐ GENERAL CONDITIONS $146,382C. SEDIMENT REMOVALC‐1 Spillway Management Unit 35,381 CY $18.00 $636,858C‐2 West Pool Management Unit 19,977 CY $20.00 $399,540C‐3 Sandbar West Management Unit 35,203 CY $15.00 $528,045C‐4 Ridge Management Unit 35,367 CY $22.00 $778,074C‐5 Sandbar East Management Unit 11,499 CY $15.00 $172,485C‐6 East Pool Management Unit 127,071 CY $20.00 $2,541,420Subtotal ‐ SEDIMENT REMOVAL $5,056,4226' dredging depth; Assume fines and sand mix, on‐site disposal, combinationof land excavation and suction dredge.2' dredging depth; Assume fines and sand mix, on‐site disposal, suctiondredge.8' dredging depth; Assume sand/gravel mix, on‐site disposal or reuse, landbasedexcavation.Includes dredging and connection channel. Assume fines and sand mix, onsitedisposal, combination of land excavation and suction dredge.4' dredging depth. Assume sand/gravel mix, on‐site disposal or reuse, landbasedexcavation.4' dredging depth; Assume fines and sand mix, on‐site disposal, combinationof land excavation and suction dredge.D. SEDIMENT FOREBAY OPTIONSD‐1 Option 1 ‐ Sediment Forebay bottom at elevation 2385 1 LS $207,670.00 $207,670 See Table 3‐3b for detailed costsD‐2 Option 2 ‐ Sediment Forebay bottom at elevation 2381 1 LS $631,412.00 $631,412 See Table 3‐3b for detailed costsE. WETLAND AREA ENHANCEMENTSE‐1 Realign Sullivan Creek and Floodplain Benches 23,768 CY $15.00 $356,520 Assume fines and sand mix, on‐site or local disposal, land‐based excavation.E‐2 Power Ck. Floodplain Benches 2,352 CY $16.00 $37,632 Assume fines and sand mix, on‐site or local disposal, land‐based excavation.E‐3 Chicken Ck. Floodplain Benches 1,873 CY $16.00 $29,968 Assume fines and sand mix, on‐site or local disposal, land‐based excavation.Subtotal ‐ WETLAND AREA ENHANCEMENTS $424,120


Table 3.1‐5a: Conceptual Level Opinion of Probable Cost for Select Components of the Phoenix Lake Preservation and Restoration Plan.Item No. Description Qty Units $/Unit Total Notes and AssumptionsTOTALSSub‐Total with Forebay Option 1 $6,831,251Sub‐Total with Forebay Option 2 $7,254,993Sub‐total average of Options 1 & 2 $7,043,122Contingency 25% $1,760,780TOTAL $8,803,902


Table 3.1‐5b: Conceptual Level Opinion of Probable Cost for Sediment Forebay Options.Option 1 ‐ Bottom of Sediment Forebay at existing ground elevation (~2385)Item No. Description Qty Units $/Unit Total Notes and AssumptionsSF‐1‐1 Clearing & Grubbing 1.5 Ac $5,000.00 $7,500 brush, including stumps.SF‐1‐2 Temporary BMPs 1 LS $25,000.00 $25,000 Includes maint. & mon. for following wet seasonSF‐1‐3 Excavation ‐ Berm Foundation 3,050 CY $3.00 $9,150 1030 LF, 40' wide, 2' deepSF‐1‐4 Hauling & Disposal 8,900 CY $12.00 $106,800 10% expansion factor includedSF‐1‐5 Compaction ‐ Sullivan Ck. Sed. Forebay 7,200 SY $3.00 $21,600SF‐1‐6 Construct Forebay Embankment 5,040 CY $3.00 $15,120 place/compact 1030 LF, 34' base, 10' top , 6' tall, 2:1 sidesSF‐1‐7 Outlet Works 1 Ea. $20,000.00 $20,000 ~20 yds. Concrete + gateSF‐1‐8 Overflow Weir Rip‐Rap Slope Armor 500 SY $5.00 $2,500 top and downstream face of overflow weirSubtotal ‐ OPTION 1$207,670 (Does not include access and property agreements)Option 2 ‐ Bottom of Sediment Forebay at elevation 2381Item No. Description Qty Units $/Unit Total Notes and AssumptionsSF‐2‐1 Clearing & Grubbing 1.5 Ac $5,000.00 $7,500 brush, including stumps.SF‐2‐2 Sediment Control 1 LS $25,000.00 $25,000 Includes maint. & mon. for following wet seasonSF‐2‐3 Excavation ‐ Basin 39,808 CY $3.00 $119,424 4' deep over area of Sed. ForebaySF‐2‐4 Hauling & Disposal 43,789 CY $10.00 $437,888 10% expansion factor includedSF‐2‐5 Compaction ‐ Sullivan Ck. Sed. Forebay 7,200 SY $3.00 $21,600SF‐2‐6 Outlet Works 1 Ea. $20,000.00 $20,000 ~20 yds. Concrete + gateSubtotal ‐ OPTION 2$631,412 (Does not include access and property agreements)


Chapter 3 – Part Ilikely require 7 to 10 days to effectively removethe bulk of the growth. Depending upon thetiming of the harvest, it is possible that onemaintenance event would be sufficient for oneyear; however, shallower locations would likelyre‐grow, requiring a second cut to maintainaesthetics and access. The estimated cost is$25,000 per harvest event.Lake Preservation & Restoration ConceptsFebruary). Costs for mowing the lake perimeterare estimated to be approximately $10,000.This estimate does not include permits andenvironmental compliance that would beneeded to conduct this activity.Mowing for FirebreaksMowing of the dense, dry stands of marshvegetation would create firebreaks to containthe spread of wildfires (Photo 3.1‐15).Photo 3.1‐15. Marsh vegetation can be mowed to providetemporary fire breaks. Note that vegetation shown in thephoto is live, current‐year growth. Mowing in PhoenixLake would likely take place when vegetation is dry.Mowing the lake perimeter, as well as dividinglarger areas by creating additional breaks wouldcontain wildfire within small areas as opposedthe potential spread to the entire lake andpotentially the surrounding watershed.Firebreaks would be delineated and presurveyedto exclude preferred or occupied birdnesting habitat. Mowing the lake perimeterwould take approximately two to four days for acut to the root crown or water level (based onanticipated plant densities). This would mostlikely be an annual or semi‐annual event as thecutting would open up areas for new growththe following season. Mowing would take placewhen the lake level is low and prior to the startof bird nesting season (likely January or3.1‐34


Chapter 3 – Part I4.0 CONCLUSIONS AND NEXTSTEPS4.1 CONCLUSIONSPhoenix Lake has served eastern TuolumneCounty as a water storage and supply facility forover 150 years. The lake is also an importantrecreational amenity and currently provideswetland functions and values that are unique tothis portion of the County. In the past 150 yearsthe lake has received minimal maintenance topreserve these functions. In the absence ofintervention many of the functions and valuesthat the lake provides will continue to bedegraded or lost.Morris et al., (2008) identify five strategies tocontrol sedimentation in reservoirs. Thesestrategies are:1. Sediment yield reductions. Thisinvolves control of sediment sources;2. Sediment storage. This strategyassumes there is sufficient storage inthe reservoir to allow forsedimentation;3. Sediment routing. This strategy passessediment around or through thestorage pool to minimize trapping;4. Sediment removal. This is removal ofstored sediment by dredging and/orflushing; and5. Sediment focusing. These aretechniques used to tactically arrange orsegregate sediments to solve localizedproblems so sediment does notinterfere with operations.Each of these strategies has been incorporatedinto the PLPRP as appropriate and feasible.Sediment yield reductions are described inChapter 2 of the PLPRP. Since its inception, thelake has been operated as a sediment storageLake Preservation & Restoration Conceptsfacility. Due to reduced lake capacity and waterquality concerns, additional strategies are nowneeded. Sediment routing does not appear tobe feasible at Phoenix Lake. Sediment removaland sediment focusing are the subject of thisreport.If implemented, the concepts presented in thisreport would extend the life of the reservoirwhile preserving the recreational, aestheticsand wetland values of the lake. Assuming anaverage annually deposition rate of 4,600 cy,removing approximately 265,000 cy ofsediment (Table 3.1‐3) would extend the life ofthe reservoir by more than 55 years 1 . Sedimentmanagement activities in wetland areas wouldfurther increase the life of the reservoir bytrapping sediment in locations that can beregularly managed with conventionalequipment. These activities would also improvewater quality in the lake.In the absence of intervention, the lake willeventually achieve complete sedimentationinfill (or full sediment balance). At that pointthe lake would be predominantly vegetatedwetlands with open water habitat primarilyassociated with the Sullivan Creek. The lakecould still be flooded with the flashboards in thesummer time, but lake depth and water qualitywould be marginal.1Lake trap efficiency is a non‐linear functionwhereby trap efficiency is highest when lakes aredeepest. As lakes fill with sediment their trapefficiency reduces. This estimate does not accountfo non‐linear changes in reservoir trap efficiency thatmay result from sediment removal activities.3.1‐35


Chapter 3 – Part ILake Preservation & Restoration Concepts4.2 Next stepsThe preservation and restoration conceptspresented in this report represent an initialapproach to improving conditions at PhoenixLake. These concepts were reviewed andrefined by TUD and the PLTF. The results of thisreview process are presented in Part II of thischapter.Outstanding technical issues to be resolved insubsequent stages of design include sedimentremoval depths, equipment access routes,materials handling, phasing, and reuse anddisposal areas. It is anticipated that additionalsubsurface investigation will be necessary toconfirm sedimentation depths and to refine thedepths and extents of sediment removal withineach of the management units. As additionaldata become available future PLPRP sedimentremoval plans may propose deeper or shallowertarget depths than those proposed in thisreport.Multiple administrative and environmentaltasks will need to be completed for furtherdevelopment of the PLPRP. These tasks includeobtaining access and easements agreements,conducting environment review andcompliance, obtaining necessary permits, andidentifying funding sources. Any proposedproject developed by TUD will requirecompliance with the California EnvironmentalQuality Act (CEQA). The public disclosure andoutreach activities that occur through the CEQAprocess may also provide a valuableopportunity for public comment on anyproposed actions. An environmentalcompliance strategy for implementing thePLPRP is detailed in Chapter 7.3.1‐36


Chapter 3 – Part I5.0 REFERENCES & GLOSSARY5.1 ReferencesBooks, Journal Articles and ReportsHorizon Water and Environment and cbec.2011a. Phoenix Lake 2010 BathymetricSurvey and Volumetric Storage Update.Phoenix Lake Preservation and RestorationPlan, Technical Memorandum #1. Preparedfor Tuolumne Utilities District. March.Horizon Water and Environment and cbec.2011b. Technical Memorandum #3:Sediment Source Control and ManagedPlan. Phoenix Lake Preservation andRestoration Plan. Prepared for TuolumneUtilities District. May.Donaldson, S. and W. Johnson. 2002. EurasianWatermilfoil Fact Sheet. University ofNevada, Reno Cooperative Extension.ESA. 2007. Tuolumne County Water QualityPlan. Final. Available online at:http://www.tcrcd.org/attachments/010_Final%20Tuolumne%20County%20Water%20Quality%20Plan.pdfLakeacccess.org. 2011. Understanding LakeEcology. Available online at:http://www.lakeaccess.org/ecology/lakeecology.htmlLake Preservation & Restoration ConceptsPhoenix Lake Task Force (PLTF). 2010b. PublicAccess to Phoenix Lake. In: Phoenix LakeTask Force. Final Report. October 6, 2010Phoenix Lake Task Force (PLTF). 2010c. AChannels and Islands Approach to WetlandsRestoration. In: Phoenix Lake Task Force.Final Report. October 6, 2010Phoenix Lake Task Force (PLTF). 2010d.Mapping of Seasonal Water and SedimentFlows into the North Eastern Area ofPhoenix Reservoir. In: Phoenix Lake TaskForce. Final Report. October 6, 2010Internet Resources and PersonalCommunicationsCalifornia Division of Safety of Dams. 2012. Listof Dams Within the Jurisdiction of the Stateof California. Accessed online on June 9,2012 at:http://www.water.ca.gov/damsafety/docs/Jurisdictional2010.pdfRhodes, Pat. 2011. Phoenix Lake Task Forcemember. Telephone conversation withKevin Fisher (Horizon Water andEnvironment). April , 2011Morris, G.L., G. Annadale, and R. Hotchkiss.2008. Reservoir Sedimentation. In: Garcia,M. H. (Ed). Sedimentation engineering:Process, management, modeling andpractice. ASCE Manual No. 110Phoenix Lake Task Force (PLTF). 2010a. PhoenixLake Dredging. In: Phoenix Lake Task Force.Final Report. October 6, 2010.3.1‐37


Chapter 3 – Part I5.2 GlossaryBathymetric: Measurement of elevation ordepth in water. Bathymetry is typically shownin contours of equal elevation. Alternatively,bathymetry can be shown as water depths.Bedload: The sand, gravel, boulders, or otherdebris transported by rolling or sliding along thebottom of a stream.Channel morphology: The physical form orshape of a stream channel.Delta: A fan‐shaped deposit of sedimentformed where moving water (e.g., stream)enters a body of standing water and deposits aportion of its sediment load.Deltaic: Of or relating to a deltaEmergent wetland: A wetland characterized byerect, rooted, herbaceous hydrophytes,excluding mosses and lichens.Eutrophic: A biologically productive type of lakedue to relatively high rates of nutrient input.Eutrophication: The process by which lakes andstreams are enriched by nutrients (usuallyphosphorus and nitrogen) which leads toexcessive plant growth ‐ algae in the openwater, periphyton along the shoreline, andmacrophytes in the nearshore zone.Fluvial: Relating to processes associatedwith rivers and streams.Full sediment balance: The final stage in thelife of a reservoir where a balance betweensediment inflow and outflow is achieved.Geomorphology: The study of landforms, theirhistory, and the processes which shape theearth’s surface.Lake Preservation & Restoration ConceptsMacrophytes: Aquatic plants, growing in ornear water that are emergent, submergent, orfloating. Macrophytes are visible with the nakedeye.Passerine: Of or relating to birds of the orderPasseriformes, which includes perching birdsand songbirds such as the jays, blackbirds,finches, warblers, and sparrowsPlanform: The shape or alignment of a channelas viewed from above.Sediment Forebay: an impoundment, basin,floodplain, wetland or other flow or sedimentstorage feature designed to dissipate theenergy of incoming runoff, and detain therunoff for initial settling of coarse sediments.Sediment: Solid fragmental materialtransported and deposited by the actions ofwater, wind or ice.Suspended load: Sediment that moves in achannel without coming in contact with thestreambed.Trap efficiency: The ratio of sediment trappedin a reservoir versus the amount that is passedthrough the reservoir, typically expressed as apercentage.Unconsolidated shore: Wetland habitats havingthree characteristics: (1) unconsolidatedsubstrates with less than 75% areal cover ofstones, boulders, or bedrock; (2) less than 30%areal cover of vegetation other than pioneeringplants; and (3) any of the following waterregimes: irregularly exposed, regularly flooded,irregularly flooded, seasonally flooded,temporarily flooded, intermittently flooded,saturated, or artificially flooded.Lacustrine: Of or pertaining to a lake.3.1‐38


Chapter 3 - Part IISediment Removal & Wetland Enhancement PlanPhoenix Lake Preservation & Restoration Plan


Chapter 3 – Part II1.0 INTRODUCTIONPart II of Chapter 3 describes the SedimentRemoval and Wetland Enhancement Plan (LakePlan) for Phoenix Lake. This Lake Plan builds oninformation presented in Part I of Chapter 3,Lake Preservation and Restoration Concepts(Concept Plan). Part I summarized lakemanagement issues including loss of storagecapacity and poor water quality and described ageneral approach to restore and improve thesefunctions. The objective of this Lake Plan is topresent a more detailed description of theactivities and methods needed to implementthe lake improvements. The Lake Plan includesthe attached 30% engineering drawings(Attachment A) and construction cost estimate.Part II is organized as follows:Section 1 ‐ IntroductionSection 2 ‐ Design ElementsSection 3 ‐ Construction Access & MaterialsManagementSection 4‐ Construction Costs & PhasingSection 5‐ Conclusions & Next StepsSection 6‐ References2.0 DESIGN ELEMENTS2.1 OverviewPhoenix Lake has been divided intomanagement units based upon the primaryphysical processes and dominant lakeconditions in these areas (Figure 3.2‐1). ThisLake Plan targets specific management actionsbased on conditions and opportunities withinthese lake management units. Overall, theapproach of the Lake Plan is consistent with theconcepts presented in Part I of Chapter 3.Sediment removal is focused in the open waterportions of the lake. Wetland enhancements,Sediment Removal & Wetland Enhancement Planintegrated with sediment management, aretargeted for the North Marsh Unit, including asediment forebay, realignment of SullivanCreek, and channel modifications on Sullivan,Chicken and Power creeks.Through discussions with the Tuolumne UtilitiesDistrict (TUD) and Phoenix Lake Task Force(PLTF), additional design elements have beenincorporated into the Lake Plan to furtherimprove water quality, expand usable storage,and reduce costs associated with materialsdisposal. These additional elements includesediment removal in the Boot Unit, deepdredging near TUD’s intake tower, and “in‐lake”sediment reuse to create beaches and habitatislands.The major design elements that comprise theLake Plan are described in the remainder ofSection 2.2.2 Sediment Removal in Open WaterManagement UnitsAs stated above, sediment removal is focused inopen water portions of lake, including theSpillway, West Pool, East Pool, Sandbar East andWest, and Ridge management units. Sedimentremoval areas are shown in Attachment A,Sheet 4.The Lake Plan also includes sediment removal inthe Boot Unit, which is dominated by emergentvegetation. Preliminary sediment removalapproaches for each management unit weredescribed in Part I of Chapter 3. In the sectionsbelow, revised and refined sediment removalapproaches for each management unit aredescribed. Where this Lake Plan differs fromthe concepts presented in Part I of Chapter 3, itis noted. Sediment removal methods for eachmanagement unit are also described below.3.2‐1


Notes: Base map courtesy of Bing mapsPhoenix Lake Preservation & Restoration PlanLake Management UnitsJuly 2012 Created By: KF Figure 3.2‐1


Chapter 3 – Part IITable 3.2‐1 summarizes the sediment removalvolumes and the resultant increase in storagecapacity for each management unit.Table 3.2‐1. Sediment Removal and Increasein Lake Storage CapacityLakeManagementUnitSedimentRemovalVolume(cubic yards)IncreasedStorageCapacity(acre‐feet)Spillway 72,900 45.1West Pool 60,900 37.6Sandbar West 45,400 28.1Ridge 49,800 30.8Sandbar East 28,300 17.5East Pool 146,500 90.5Boot 31,900 19.7Total 435,700 269Spillway UnitSediment removal at the Spillway Unit has beenmodified from the Concept Plan to includedredging up to the spillway structure.Previously, it was assumed that access to thespillway structure would be impeded by theTUD pipeline. Upon further consideration, itwas determined that the benefits of dredgingthe area between the pipeline and spillwayoutlet likely outweigh the costs associated withtemporarily relocating or replacing this sectionof the pipeline. The existing pipeline is alsoundersized, which further warrants itsreplacement.The majority of the Spillway Unit would bedredged to a target elevation of 2,365 feet 1 (ft).The presence of shallow bedrock or native1 All elevations are referenced to North AmericanVertical Datum (NAVD) 88.Sediment Removal & Wetland Enhancement Plansubstrate near the lake shoreline may result inactual dredging depths that are shallower thanthe target elevation. Deeper dredging isproposed in the portion of this unit that isclosest to the intake tower (See West Pooldescription for details).Sediment removal in this unit may beaccomplished through a combination of waterbaseddredging and land‐based excavation withequipment operating from the dam.Approximately 72,900 cubic yards (cy) ofsediment would be removed from this unit(Table 3.2‐1). If moved by excavationequipment, this material could be placeddirectly in the proposed sediment disposal areaon the land‐side of the dam (Attachment A,Sheet 12). Material moved by water‐basedsuction dredging equipment would bedewatered first and then moved to a reuse ordisposal location (See Section 3).West Pool UnitSediment removal in the West Pool Unit hasbeen expanded to include deep dredging in thevicinity of the intake tower (Attachment A,Sheet 4). The intake tower has 3 gates that canbe used to draw water from the lake; thedeepest gate is at elevation 2,349 ft. TUD wouldlike to have the ability to draw water from thisgate during low water conditions. Furthermore,the quality of water drawn from this gate maybe superior to the shallower gates, particularlyin the summer months when watertemperature and biological productivitydecrease with depth. As such, the Lake Planincludes dredging to elevation 2,347 ft in thevicinity of the tower. The 2 ft over‐excavationaround the gate would allow for a modestamount of sediment settling and accumulationto occur without impacting gate operability. TheLake Plan also includes retaining a small earthenberm approximately 30 ft from the tower to3.2‐3


Chapter 3 – Part IIminimize sediment infilling at the base of thetower (Attachment A, Sheets 4 and 13).Most of the sediment removal in the West PoolUnit will require likely water‐based dredging,though temporary dewatering of the lake mayalso be feasible. Some land‐based excavation isalso likely feasible in the areas closest to thedam. Approximately 60,900 cy of sedimentwould be removed from this unit (Table 3.2‐1).Sandbar West UnitSediment removal in this unit is similar to thatproposed in the Concept Plan. Key featuresinclude excavating a channel in the unit’snorthwest portion to connect to the 1986dredge hole, thereby eliminating the “deadstorage” (i.e., unusable storage) in the dredgehole. The Lake Plan also includes gradingtransition slopes at 3h:1v (3 horizontal to 1vertical) from the sediment removal area to theexisting marsh to reduce erosion potential.Access for sediment removal could beaccomplished by constructing a temporary inlakehaul route that connects to Phoenix LakeRoad (Attachment A, Sheet 4), or by operatingsmall barges on the lake to move material toanother access point. Approximately 45,400 cyof sediment would be removed from this unit(Table 3.2‐1).Ridge UnitSediment removal is proposed in the northwestportion of the unit that is contiguous with theWest Pool and Sandbar West units. Dredging achannel to connect the East and West Pools isproposed in the southern portion of the unit toreduce the dead storage volume in the EastPool. The plan for this unit includes reusingexcavated sediment to create a habitat island(See Section 2.4), thereby reducing disposalcosts while providing an environmental benefit.Sediment Removal & Wetland Enhancement PlanSediment removal methods for this unit arelikely to include both land and water‐basedequipment. Approximately 49,800 cy ofsediment would be removed from this unit(Table 3.2‐1).Sandbar East UnitA modest excavation depth (2,370 ft) isproposed for the Sandbar East Unit because ofthe high likelihood of competent, nativematerial near the lake bed. The targetexcavation depth(s) for this unit may be refinedwith subsurface investigations conducted insubsequent phases of design. Sediment removalin this unit would likely be accomplished withconventional land‐based excavation equipmentloading trucks that use a temporary in‐lake haulroute connected to Phoenix Lake Road.Approximately 28,300 cy of sediment would beremoved from this unit (Table 3.2‐1).East Pool UnitSediment removal in this unit is similar to thatproposed in the Concept Plan, however, theLake Plan includes substantial placement ofsediment on the east side of the lake to create abeach and expand an existing island. Details ofthese features are described in Section 2.4.Based on guidance from TUD and the PLTF,temporarily dewatering the lake to enablesediment removal with land‐based equipment islikely feasible from a water supply operationsstandpoint, as well as agreeable tohomeowners. It is anticipated that a temporarycofferdam, such as a Portadam®, placed alongthe mid‐lake ridge would allow for dewateringof the East Pool. Low ground pressureequipment would be used to excavateapproximately 146,500 cy of sediment from thisunit (Table 3.2‐1).3.2‐4


Chapter 3 – Part IIBoot UnitWhile the Concept Plan did not includesignificant sediment removal in the Boot Unit,opportunities to provide additional storagecapacity in this unit were reconsidered.Through consultation with TUD and the PLTF,and further consideration of lake sedimentationprocesses, it was concluded that sedimentremoval in the Boot Unit is warranted. Asdescribed in the Part I of this chapter,sedimentation in the Boot Unit is largely theresult of backwater settling and windcirculationinduced deposition of fine sediment.Sediment removal in the Boot Unit wouldcreate new depositional capacity and allow theBoot to continue to function as a “kidney” forthe lake by trapping fine sediment. In the longterm,if watershed‐based sediment sourcecontrol measures are implemented, thedepositional rates in the Boot should decline.The proposed sediment removal plan for theBoot Unit includes dredging wide, deepchannels and maintaining wetland islands(Attachment A, Sheet 7). Retaining wetlandislands in the unit will preserve and enhancebird nesting habitat. The island habitat wouldbe separated from uplands by channels, whichwould reduce predation on bird nests. Thechannels would also provide a fuel breakbetween wetland and upland areas.Sediment removal in this unit would likely beaccomplished with conventional land‐basedexcavation equipment loading trucks that usethe temporary in‐lake haul route.Approximately 31,900 cy of sediment would beremoved from this unit (Table 3.2‐1).Sediment Removal & Wetland Enhancement Plan2.3 North Marsh SedimentManagement & WetlandEnhancementThe wetland enhancement and sedimentmanagement activities in the North Marsh Unitare similar to those proposed in the ConceptPlan. The design elements include a sedimentforebay on Sullivan Creek at the lake transitionzone, a realigned Sullivan Creek channel intothe lake, and floodplain benches to storesediment on Chicken and Power creeks(Attachment A, Sheet 5). The objectives of thesedesign elements are to: (1) reduce directsediment loading into the lake from Sullivan,Chicken, and Power creeks, (2) manage andreduce the encroachment and expansion ofwetlands into the open water lake, (3) improvehabitat diversity, and (4) provide fuel breaks.The rationale for these objectives is described inPart I of this chapter. Key aspects of each designelement follow.Sullivan Creek Sediment ForebayThe Sullivan Creek sediment forebay (forebay) isintended to trap bedload and coarse suspendedload (e.g., sand and coarser) sediments beforethey are delivered to Phoenix Lake. A keyfunction and benefit of such a forebay is that itfacilitates routine maintenance and sedimentremoval more easily than open lake sedimentdredging.In Part I of chapter, two options were presentedwhich primarily differed in the elevation of theforebay. Option 1, placed the bottom of theforebay at the existing wetland surface, andcreated a basin through construction of aperimeter berm. Option 2 proposed excavatingthe forebay into (and below) the wetlandsurface, thereby creating a basin in thesurrounding area. Upon further considerationand inspection of topographic data, Option 23.2‐5


Chapter 3 – Part IIwas selected and subsequently refined as thepreferred alternative. This option waspreferred for the following reasons:• The weir controlling water surface elevation(WSE) for Option 2 would be several feetlower than Option 1. This would result inlower WSEs in the forebay, and upstreamon Sullivan Creek. Maintaining higher WSEson Sullivan Creek could have increased thepotential flood risk and raised the localwater table;• The at‐grade forebay (Option 1) would havecreated a backwater condition that wouldhave extended upstream into SullivanCreek, creating the potential for increasedsediment deposition within the channel,resulting in the need formaintenance/removal of sediment outsideof the forebay area, as well as increasingpotential flood risk; and• The Option 2 design does not requiregeotechnical engineering of the forebaycontainment berms, and carriesconsiderably less risk of berm failure ifovertopped during an extreme flood event.The conceptual design for the forebay is shownin Attachment A, Sheet 9. The forebay wasdesigned to be large enough to effectively trapsediment and minimize the frequency ofmaintenance. The proposed usable volume is3,310 cy. This equates to 70% of the estimatedaverage annual deposition in the lake. TheSullivan Creek watershed accounts for 67% ofthe lake’s contributing drainage area. While allsub‐watersheds draining to the lake are notlikely to contribute sediment proportionally, it isanticipated that the Sullivan Creek forebay willhave sufficient capacity to capture the expectedSediment Removal & Wetland Enhancement Planannual delivery of coarse suspended load andbedload.The bottom of the forebay would slope fromelevation 2379.5 ft at the upstream northerninlet, to 2379 ft at the southern outlet. Theadjacent ground is at elevation 2,385 ft, thusthe forebay would be roughly 5 to 6 ft deep.These elevations optimize sediment storagevolume, while keeping the forebay at theordinary winter water level (OWLL) of 2379 ft,thus allowing for maintenance/sedimentremoval on the shoulders of a typical wetseason (i.e., March‐April or October‐November).The forebay inlet weir is sized to accommodatea 10‐year return storm flow (Q10) ofapproximately 1,400 cubic feet per second (cfs)(See Technical Appendix II for estimates ofstream flow). The inlet weir is a two‐tier design,with a low‐flow weir sized to accommodate a 2‐year return storm flow (Q2 = 436 cfs), and anadjacent, elevated high flow weir that isdesigned to pass the Q10 (Attachment A, Sheet13). The inlet weir is set slightly above theexisting grade of Sullivan Creek channel and canbe blocked with flashboards or sandbags toshunt flows into the existing Sullivan Creekchannel during forebay maintenance, or periodsof forebay bypass.A diversion weir for the existing Sullivan Creekchannel was designed in conjunction with theforebay inlet weir (Attachment A, Sheet 9). Thediversion weir is intended to divert flows up toQ10 into the forebay. Flows in excess of Q10would overtop the diversion weir and flowdown the existing Sullivan Creek channel. Thediversion weir also incorporates a sluice gate toallow low flows to pass into existing SullivanCreek during maintenance/bypass of theforebay.3.2‐6


Chapter 3 – Part IIThe forebay outlet weir is also a two‐tier design.The two tiers are designed so that Q2 passesthe lower tier and the upper tier passes Q10,while maintaining 1 ft of freeboard to the top ofthe forebay embankments. The forebay outletweir would be armored with riprap to preventerosion.All, or a majority of the basin will be inundatedduring the summer when the lake level is high.Flashboards could potentially be installed tohelp keep the forebay dry. However, thissolution may not be practical, as the length ofthe high flow outlet weir is approximately 230 ftat an elevation of 2384 ft. Because the forebaywould be inundated at the OSLL (withoutflashboards), maintenance (i.e., sedimentremoval) would likely be performed before orafter summer, when water levels do notinundate the forebay.Preferably, maintenance would be scheduledprior to raising lake levels, in late March orApril, after the majority of the wet seasonstorms have passed. At that time, operatorscould open the sluice gate in the Sullivan Creekdiversion weir and install flashboards or sandbags across the low‐flow inlet weir to theforebay, allowing creek flows to bypass theforebay. Once the forebay is dry enough toallow passage of earth moving equipment, theforebay can be cleared of sediment down todesign elevations. The excavation equipmentwould access the forebay from an earthen bermconstructed around the perimeter of theforebay. Sediment could be hauled off‐siteimmediately, or stockpiled nearby, allowed todry out further, and then transported off‐site.The forebay design also includes a drain pipe togravity drain ponded water from the forebaywhich is unable to exit through the outlet weir.This drain pipe would connect back to theexisting Sullivan Creek channel.Sediment Removal & Wetland Enhancement PlanSullivan Creek RealignmentAs described in Part I of this chapter, the mainpurpose of the Sullivan Creek channelrealignment is to promote sediment depositionin existing wetland areas. Attachment A, Sheets9 and 10 show the preliminary design forrealignment of the Sullivan Creek channel. Theproposed design is similar to that presented inthe Concept Plan, with the main differencebeing that the channel has been moved furtherto the south and east. This was done tominimize the potential for the new alignment torecapture the existing channel.The low flow inset channel for the newalignment of Sullivan Creek was designed toconvey flows roughly equivalent to half of Q2.The channel was intentionally undersized topromote frequent overtopping of its banks andinundation of the adjacent excavatedfloodplain. Typically as flows leave the mainchannel, the cross‐sectional flow area androughness drastically increase, thereby reducingvelocity and increasing sediment deposition.Hydraulic analysis of the design channel will benecessary to refine its sizing and assess channelstability. This will likely be performed insubsequent design phases of the PLPRP. Erosionprotection measures, such as leaving existingwetland vegetation in place along the marginsof the channel at high energy locations, couldprovide additional stability to the channel.Floodplain BenchesFloodplain benches are proposed for theSullivan, Power and Chicken creek channels.The purpose of the floodplain benches is to trapsome portion of the sediment delivered fromthese drainages. In addition to improvingsediment trapping, the new floodplains wouldprovide temporary fuel breaks. Over time, thefloodplain benches would increase in elevation3.2‐7


Chapter 3 – Part IIand vegetation would become established.Alternatively, the floodplain surfaces could bemaintained at a prescribed elevation tomaximize sediment trapping and fuel breakfunctions. It is estimated that sediment removalon the floodplains would need to occur every 3‐5 years, or following large flood events (e.g., 10‐year flood). Sediment removal may require theuse of low ground pressure excavators and haultrucks. The equipment would access thefloodplain via pre‐established routes. Thefloodplain maintenance program could beincorporated into the regulatory permits for thePLPRP (See Chapter 7) to alleviate the need topermit each sediment removal event on anindividual basis.The floodplain benches on Sullivan Creek wouldvary in width from approximately 40 to 120 fton either side of the low flow channel(Attachment A, Sheet 13). The benches onPower and Chicken creeks would be 20 feet oneither side of the channel. It is anticipated thatchannel construction and floodplain benchingwould be accomplished with conventional landbasedexcavation equipment operating ontemporary haul roads or mats. Construction ofthe new Sullivan Creek channel and associatedfloodplain benching would result in removal ofapproximately 29,900 cy of sediment (Table 3.2‐1). Approximately 1,100 cy of sediment wouldbe removed to create floodplain benches onPower and Chicken creeks. Most of thissediment would be removed from the lake.Some material may be placed into existingmarsh areas to provide topographic relief,which would increase habitat diversity.2.4 Beach & Habitat IslandsReusing dredged material to create beachesand islands within the lake has several potentialbenefits including: (1) providing habitatdiversity; (2) reducing costs, traffic andSediment Removal & Wetland Enhancement Plangreenhouse gas emissions associated withsediment disposal; and (3) creating recreationalamenities.BeachesBeach creation is proposed on the south side ofthe East Pool Unit near Phoenix Lake Park(Attachment A, Sheet 6). Sandy materialexcavated from other portions of the lake (e.g.,Sandbar West Unit) would be placed along theshoreline. Most of the beach would be atelevation 2,387 ft, which is approximately 2 feetabove ordinary summer lake level (OSLL). A 12‐ft wide channel would bisect the beach to allowfor boat launching and storm water dischargefrom an existing drainage.The beach would be designed so that itgradually slopes into the lake. Creation of thebeach would reuse approximately 31,000 cy ofdredged material that would otherwise behauled to a sediment disposal area.The beach may require some maintenance suchas raking to minimize the accumulation oforganic matter and reduce the potential forgrowth of vegetation. The PLTF has alsodiscussed the potential for beach creation onthe north side of the lake near the Apple ValleyEstates.Habitat IslandsIsland creation or expansion is proposed in theEast Pool and Ridge units. The primary reasonsfor creating island habitat are to reuse sedimentand to minimize the loss of importantwaterfowl resting/loafing habitat, which ischaracterized by nonvegetated, unconsolidatedshoreline areas such as the Sandbar Unit. Theexisting island in the East Pool (Photo 3.2‐1)would be expanded by placing dredged materialaround the margins of the island (AttachmentA, Sheet 6).3.2‐8


Chapter 3 – Part IISediment Removal & Wetland Enhancement Planoptions are discussed in Part I of this chapter. Itis anticipated that public and resource agencyinput received during the regulatory complianceand design phase of the PLPRP will influencesubsequent designs for sediment removal andwetland management.3.0 CONSTRUCTION ACCESS &MATERIALS MANAGMENT3.1 Construction AccessPhoto 3.2‐1. The proposed plan would expand theexisting island (shown on the left side of the photo) toprovide loafing (resting) habitat for waterfowl.A new island is also proposed near the center ofthe lake in the Ridge Unit (Attachment A, Sheet8). The target elevation for both of these islandswould be approximately 2,381 ft. This elevationwould provide loafing habitat for waterfowl inthe winter months. The islands would besubmerged in the summer time. Creation of theislands would reuse approximately 5,800 cy ofdredged material that would otherwise behauled to a sediment disposal area. It isanticipated that the extent and design of theislands will be refined in subsequent phases ofthe PLPRP through consultation with resourceagencies such as the California Department ofFish and Game.2.5 Other Options ConsideredOther sediment removal and wetlandmanagement options considered in thedevelopment of this Plan included: (1) deeperdredging in open water portions of the lake, (2)the “Channels and Islands” approachrecommended by the PLTF (PLTF, 2010), and (3)complete open water lake restoration (i.e.,converting all wetlands to open water). Thepotential benefits and drawbacks of theseConstruction access points are similar to thoseidentified in the concept Plan. The potentialaccess points include Lori Lane at Phoenix LakePark, Phoenix Lake Dam, the existing boat rampat Apple Valley Estates, and the Cedar RidgeApple Ranch in the vicinity of the proposedsediment forebay.In addition to these sites, a temporary, in‐lakehaul road is proposed along the lake shorelinein the Sandbar East, East Pool and Bootmanagement units (Attachment A, Sheet 4).This temporary road would connect directly toPhoenix Lake Road, which would allow landbasedexcavation equipment to removesediment from the Sandbar and Boot units.Establishing this road would require aneasement over private property between thelake and Phoenix Lake Road.Several of the construction access points listedabove are also identified as potential locationsfor establishing public access to the lake(Chapter 5, Public Access Plan). The planning forconstruction activities and public access will becoordinated so that sites can serve the multipleobjectives of the PLPRP.3.2‐9


Chapter 3 – Part II3.2 Materials HandlingMaterials handling includes the necessaryprocedures to prepare sediment for beneficialreuse or disposal. Several factors may influencethe materials handling procedures includingremoval location and methods, sedimenttexture, project phasing, and adjacentlandowner cooperation/participation.As discussed in Section 2.2, it will likely bebeneficial to draw down the lake and removesediment from the East Pool with land‐basedexcavation equipment. It is anticipated thatmuch of the sediment removed from the EastPool would be loaded on to trucks and hauledoff‐site for reuse or disposal. During theexcavation of the East Pool, it may be feasibleto construct a settling basin near Lori Lane tohandle hydraulically dredged sediment from theWest Pool and Spillway units. This would allowthese materials to dewater for later removalwith land based equipment. Alternatively,sediment that is hydraulically dredged from thewestern portion of the lake could be dewateredin the settling basin that was used in the 1986dredging event.The land‐side, southeast, of the dam is anotherpotential location for dredged materialshandling. Sediment may be placed at thislocation with a long‐reach excavator orclamshell dredge operating from the dam orpumped directly to this area with suctiondredge equipment. If this area is used to handlesediment delivered directly from a suctiondredge operating in the lake, then substantialsite modifications would be required includingconstruction of a settling basin.Sediment Removal & Wetland Enhancement Plan3.3 Beneficial Reuse & DisposalResults of Preliminary Sediment TestingA preliminary screening of sediment chemistryand texture (i.e., particle size distribution) wasconducted to inform potential reuse anddisposal options for sediments excavated fromthe lake. On April 26, 2011 sediment sampleswere collected at 5 locations within the lake(See Attachment B). At each sampling station, 3core samples were collected from 0 to 3 ftbelow the sediment surface. In some instances,sediment could not be retrieved with the coresampler (due to consistency of the sediment),so the samples were collected with a shovel. Acomposite sample from each station was sentto BSK Analytical Laboratories in Fresno, CA fortesting. Analyses included: general chemistry,nutrient concentrations, total metalsconcentrations, Waste Extraction Test (WET)metal concentrations, and particle sizedistribution.The laboratory results of the sediment testingare provided in Attachment B. The pH of lakesediments ranged from 5.2 to 5.8, which ischaracterized as moderate to strongly acidic.The acidity of the lake sediments may berelated to several factors including vegetationcover in the watershed (i.e., coniferous forest),chemistry of the parent material, and/oroxidation of organic matter in the lake. The pHlevels measured in the lake sediments do notnecessarily limit the potential for beneficialreuse, but certain reuse options (e.g.,agricultural or restoration) may require a soilamendment such as lime (CaCO 3 ) to establish aneutral pH.The initial screening of nutrient concentrationin the sediment samples included analysis oftotal nitrogen (N), and nitrate and nitrite. TotalN in California soils may vary greatly, but3.2‐10


Chapter 3 – Part IIcommonly ranges from 0.1 to 0.3% of the totalsoil volume (Singer, 2003). Total N in thesediment samples ranged from approximately0.06 to 0.1%. Nitrate and nitrite, which aresoluble forms of nitrogen, were very low ornon‐detectable in all samples. The laboratoryalso reported results for total phosphorus (P);the levels present in the sediment samples arenot a concern for sediment reuse or disposal.The Central Valley Regional Water QualityControl Board (Central Valley RQWCB) providedthe consultant team with a list of Constituentsof Concern (COCs) to analyze during pre‐dredgesampling (See Attachment B). The list of COCsincludes a suite of metals that are commonpollutants. The concentrations of the COCs in allsamples were within the range of naturallyoccurring background concentrations(Wedepohl, 1995), and below levels that areconsidered toxic by the State (See Tables 1 and2 of Title 22, Chapter 11, Article 3, Section66261.24 in Attachment B). Mercury, a metalcommonly associated with legacy gold miningactivity, was not detected in any of the samples.Sediment texture ranged from silt loam in theBoot Unit to loamy sand in the Ridge Unit. Allsamples had a relatively high percentage ofsand and much lower clay content. In mostlocations, the surface material was finer thanthe substrate at depth greater than 1 to 2 feetbelow the surface. Since the samples at eachstation were homogenized, this stratification isnot evident in the data.Results of the preliminary screening suggestthat sediment in the shallow surface of the lake(i.e., 0 to 3 ft) is not likely to be classified ashazardous waste, and it is potentially suitablefor a wide range of reuse applications. It isimportant to note that sediment samples werecollected only from 0 to 3 ft below the surface,Sediment Removal & Wetland Enhancement Planand therefore may not be representative of allthe sediment that is proposed to be removedfrom the lake. A more robust sediment testingprogram will be developed in coordination withthe Central Valley RQWCB during the designand regulatory compliance phase of the PLPRP.Potential Reuse and Disposal OptionsTable 3.2‐2 lists potential reuse and disposaloptions for sediment removed from the lake.These options represent a broad range ofopportunities for sediment reuse or disposal.The table provides a general description of eachoption, approximate area and volume availablefor reuse/disposal, and estimated relative costs.At this stage of the planning process it ispremature to determine which of the reuse ordisposal options will be utilized. For each optionlisted in Table 3.2‐2 action items have beenidentified to advance the planning for reuse ordisposal. As is the case with most projects, costwill be the primary factor in determining thepreferred option(s). The options that are likelyto cost the least are those closest to the lake.However, there may not be sufficient orsuitable disposal sites in the immediate vicinityof the lake. Costs will increase with distancefrom the lake, as will environmental impactsassociated with greenhouse gas emissions andtraffic.Depending on construction methods, a largeportion of the sediment proposed to beremoved from the lake will need to be loadedinto trucks and hauled to a disposal site (orsites). Assuming that each truck canaccommodate 10 to 12 cy per trip, the entireproject could generate more than 30,000 trucktrips. This high volume of truck travel is likely toimpact local roads. These aspects of the projectwill be considered during subsequent planningand environmental review phases of the PLPRP.3.2‐11


Table 3.2‐2. Sediment Reuse and Disposal Options for Phoenix LakeDisposal/Reuse Area General Description ApproximateArea(acres)ApproximateVolume Availablefor Reuse/Disposal(cubic yards ‐ dry)Estimated RelativeCostPlanning Action ItemPhoenix Lake DamMaterial disposal on land‐side of dam.Area was previously used for materialsdisposal. TUD owns property. Dredgedmaterial could be used to build a newaccess road to connect the dam withMeadow Brook Drive.TBD25,000 ‐ 50,000 cy;potentially greater ifconstructing a newaccess road.Low for disposal only;High for new access.> Collect topographic data> Delineate disposal area> Coordinate deposal plan with DSOD> Investigate easement options for long‐termaccess.North (1986) DisposalAreaArea was previously used for materialsdisposal. Existing (dry) material could beexcavated and placed in adjacent orchardsto make room disposal.16 acres(8 upland and 8wetland/riparian)100,000 ‐ 250,000 cy Low‐Moderate > Coordinate with property owner> Conduct survey of pond area> Evaluate existing zoning/land userestrictionsApple orchard fieldsPhoenix Lake CountryClubPlace sediment in orchards to improvedrainage/level fields.Provide fill material for golf courseimprovements/maintenance15 ‐ 20 acres 100,000 cy Low > Coordinate with property ownerTBD TBD Low‐Moderate > Coordinate with owner to determine ifany large project are planned and potentialstockpile capacitySierra Pines Property TUD property in Twain Harte. TBD TBD Low‐Moderate TBDJamestown Mine Abandoned mine approximately 9 milesfrom Phoenix Lake. Severalreclamation/development project areplanned in the area.300+ acres Likely unlimited Low‐Moderate > Communicate with owner to determinematerial needs and stockpiling capacityConstruction fillmaterial/commerciallandscaping/ aggregateReuse material for commerciallandscaping or aggregate. Sand is theprimary reusable material.NA TBD Low‐Moderate > Contact local landscaping and aggregatecompanies to determine their needs andstockpiling capacity.Local landfillOther agricultural useCDFG Merced RiverRanchMaterial may be suitable for landfill dailycover or cappingLand application in field or pastures of thefoothills or Central ValleyRiparian restoration site near Snelling.Approximately 40 miles from PhoenixLake. Fines may be more desirable thansand.NA TBD Moderate > Contact local landfills to determine theirneeds and stockpiling capacity.NA TBD Moderate > Contact local agricultural commissioners orfarm bureaus300+ acres TBD High > Limited primarily by cost, but could begrant funded.> Further coordination with CDFG is needed.


Chapter 3 – Part IISediment disposal costs may be reduced byidentifying grant funding for beneficial reuse ofsediment such as habitat restoration, landconservation or reclamation. Timing of thesediment removal will also be an importantfactor as the need for material at reuse/disposalsites may change. The list of options should beperiodically updated as information becomesavailable.4.0 CONSTRUCTION COSTS &PHASING4.1 Conceptual Cost EstimateTable 3.2‐3 provides conceptual level costestimates for implementing the Lake Plan. Thecost estimate does not account for inflation orlong‐term maintenance of the sediment forebayand floodplains in the wetland areas. At thisstage of the design development it is difficult toidentify which specific parcels and easementswill be necessary to implement the project.Thus, Table 3.2‐3 includes an estimated cost foracquisition of land for the sediment forebay andrealignment of Sullivan Creek, but not for otheracquisitions or easements that may be requiredfor construction and maintenance access.4.2 PhasingAs mentioned in the Concept Plan, severalfactors may influence the schedule forimplementing the Lake Plan including funding,environmental permitting, and land acquisitionor access agreements. At this juncture, fundingis considered the most significant obstacle tocompleting the Lake Plan. The Lake Plan hasbeen developed so that it can be implementedin segments or phases. However, it is importantto recognize that costs for completing severalsmall projects will be substantially higher thanfor a single, large project. This is particularlySediment Removal & Wetland Enhancement Plantrue for projects that involve water‐baseddredging equipment, which require significantmobilization costs.In the absence of funding and administrativeconstraints, the following phasing plan isrecommended:Phase 1:• Construct Sullivan Creek sedimentforebay and wetland enhancementsPhase 2:• Complete land‐based sediment removaloperations in open water (See Table3.2‐3)• Construct beaches and islands• Construct East‐West Pool connectionchannelPhase 3:• Complete water‐based sedimentremoval operations in open lake (SeeTable 3.2‐3)• Construct West Pool‐Dredge Poolconnection channelAs discussed in the Concept Plan, it would beprudent to have watershed BMPs in place thatwould reduce sediment loading to Phoenix Lakeprior to implementing the Lake Plan. Similarly,it is advantageous to develop the Sullivan Creeksediment forebay and associated wetlandenhancements in Phase 1 prior to other openwater sediment removal actions.Phase 2 would consist of large‐scale, land‐basedsediment removal in the open lake, which islikely to be more cost‐effective than waterbaseddredging. It is anticipated that it will befeasible to remove sediment from the East Poolwith land‐based excavation after the unit hasbeen temporarily dewatered. Much of this3.2‐13


Table 3.2‐3. Conceptual Level Opinion of Probable Construction Costs.Item No. Description Qty Units $/Unit Total Notes and AssumptionsA. AQUISTIONS, ENGINEERING, ENVIRONMENTAL PERMITS & COMPLIANCE, ADMINISTRATIONLand Acquisition for SedimentA‐1 Forebay 9 Ac $31,500.00 $283,500A‐2 Access and Easement Purchases TBD TBD TBD 0LandandFarm.com average cost/acre inSonora. Includes sediment Forebay and aportion of realigned Sullivan CreekA‐3A‐4Engineering ‐ Sediment Removal,Forebay, Outlet Structures, Beachesand Channels, Sediment Disposal 1 LS $350,000 Horizon/cbec estimateEnvironmental Compliance andPermitting 1 LS $300,000 Horizon/cbec estimateSubtotal $933,500B. GENERAL REQUIREMENTSB‐1 Mobilization/Demobilization 1 LS $412,88310% of est. cost of water‐based work, 2% ofest. cost of land‐based workB‐2 Construction Surveying 120 hr $230.00 $27,600 2‐man crew, Construction StakingB‐3 Environmental BMPs $75,000 Horizon/cbec estimateSubtotal ‐ GENERAL CONDITIONS $515,483C. SEDIMENT REMOVAL & DISPOSAL ‐ Hydraulic or clamshell dredgingC‐1 Spillway Unit 72,900 CY $18.00 $1,312,200C‐2 West Pool Unit 60,900 CY $22.00 $1,339,800C‐3 Dredge Pool/West Pool Connection 5,600 CY $22.00 $123,200Subtotal $2,775,200Assume fines and sand mix, on‐site disposal,combination of land excavation and suctiondredge.Assume fines and sand mix, on‐site disposal,suction dredge.Assume fines and sand mix, on‐site disposal,combination of land excavation and suctiondredge.D. SEDIMENT REMOVAL & DISPOSAL ‐ Land‐based excavation equipmentD‐1D‐2D‐3D‐4East Pool UnitExcavation 146,500 CY $5.00 $732,500Hauling & Disposal 108,233 CY $16.50 $1,785,845Sandbar West UnitExcavation 45,400 CY $5.00 $227,000Hauling & Disposal 43,130 CY $16.50 $711,645Sandbar East Management UnitExcavation 28,300 CY $5.00 $141,500Hauling & Disposal 27,155 CY $16.50 $448,058Ridge UnitExcavation 44,900 CY $5.00 $224,500Hauling & Disposal 38,775 CY $16.50 $639,788Assumes dewatering of East PoolIncludes 5% volume reduction. Haul to local(within 20 minutes) site. $100/hr fortrucking, 20 cy per load (truck and transfer).Assume sand/gravel mix, on‐site disposal orreuse, land‐based excavation.Includes 5% volume reduction. Haul to local(within 20 minutes) site. $100/hr fortrucking, 20 cy per load (truck and transfer).Includes 5% volume reduction. Haul to local(within 20 minutes) site. $100/hr fortrucking, 20 cy per load (truck and transfer).Does not include East Pool/West PoolConnector Channel volumeIncludes 5% volume reduction. Does notinclude Mid‐Lake Island volume. Haul tolocal (within 20 minutes) site.D‐5Boot UnitClearing & Grubbing 3 Ac $5,000.00 $15,000 brush, including stumpsExcavation 31,900 CY $5.00 $159,500Hauling & Disposal 27,550 CY $16.50 $454,575Includes 5% volume reduction. Haul to local(within 20 minutes) site. $100/hr fortrucking, 20 cy per load (truck and transfer).East Pool/West Pool Connector Channel ExcavationExcavation 4,900 CY $5.00 $24,500D‐6Hauling & Disposal 4,230 CY $16.50 $69,795Subtotal $5,634,205E. BEACH & ISLAND CREATIONIncludes 5% volume reduction. Haul to local(within 20 minutes) site. $100/hr fortrucking, 20 cy per load (truck and transfer).


Table 3.2‐3. Conceptual Level Opinion of Probable Construction Costs.Item No. Description Qty Units $/Unit Total Notes and AssumptionsE‐1Beach ConstructionHauling 26,745 CY $2.50 $66,863Finish Grading ‐ Slopes 11,200 SY $0.14 $1,568Includes 5% volume reduction. Haulingwithin site.E‐2E‐3East Pool Island ConstructionHauling 1,605 CY $2.50 $4,013 Hauling within site.Finish Grading ‐ Slopes 4,000 SY $0.14 $560Ridge Unit Island ConstructionHauling 4,200 CY $2.50 $10,500 Hauling within site.Finish Grading ‐ Slopes 10,900 SY $0.14 $1,526Subtotal $85,029F. SEDIMENT FOREBAY & WETLAND ENHANCEMENTSF‐1F‐2Sullivan Creek Diversion StructureEmbankment/Compaction 300 CY $5.00 $1,500 weir embankmentHauling 260 CY $2.50 $650Includes 5% volume reduction. Haul withinsite.Rip‐Rap Slope Armor 200 SY $5.00 $1,000 inlet and outlet protectionGravel Road, 6" depth 90 SY $5.00 $450 inlet and outlet protectionOutlet Works 1 Ea. $20,000.00 $20,000Sediment ForebayTemporary BMPs 1 LS $25,000.00 $25,000Includes maint. & mon. for following wetseasonClearing & Grubbing 3 Ac $5,000.00 $15,000 brush, including stumpsExcavation 18,180 CY $5.00 $90,900Embankment/Compaction 1,120 CY $5.00 $5,600 weir embankmentFinish Grading ‐ Slopes 2,820 SY $0.14 $395 not including weirCompaction ‐ Forebay BottomSurface 7,740 SY $3.00 $23,220Rip‐Rap Slope Armor 4,775 SY $5.00 $23,875 inlet and outlet protectionHauling & Disposal 15,700 CY $16.50 $259,050Outlet Works 1 Ea. $20,000.00 $20,000Includes 5% volume reduction. Haul to local(within 20 minutes) site. $100/hr fortrucking, 20 cy per load (truck and transfer).Realigned Sullivan CreekClearing & Grubbing 9 Ac $5,000.00 $45,000 brush, including stumpsF‐3Excavation 29,900 CY $5.00 $149,500 Low flow channel and floodplain benchesHauling & Disposal 25,825 CY $16.50 $426,113Includes 5% volume reduction. Haul to local(within 20 minutes) site. $100/hr fortrucking, 20 cy per load (truck and transfer).Power Creek Floodplain BenchesAssume fines and sand mix, on‐site or localdisposal, land‐based excavation.Clearing & Grubbing 0.4 Ac $5,000.00 $2,000 brush, including stumpsF‐4Excavation 700 CY $5.00 $3,500 Low flow channel and floodplain benchesHauling & Disposal 605 CY $16.50 $9,983Includes 5% volume reduction. Haul to local(within 20 minutes) site. $100/hr fortrucking, 20 cy per load (truck and transfer).Chicken Creek Floodplain BenchesAssume fines and sand mix, on‐site or localdisposal, land‐based excavation.Clearing & Grubbing 0.7 Ac $5,000.00 $3,500 brush, including stumpsF‐5Excavation 400 CY $5.00 $2,000 Low flow channel and floodplain benchesHauling & Disposal 345 CY $16.50 $5,693Subtotal $1,133,927G. EAST POOL DEWATERINGG‐1 Water Dam Installation 1 LS $32,750.00 $32,750Subtotal $32,750TOTALSIncludes 5% volume reduction. Haul to local(within 20 minutes) site. $100/hr fortrucking, 20 cy per load (truck and transfer).Assume 3' of water impounded. Includesrental and installation.Subtotal $11,025,064Contingency 10% $1,102,506TOTAL $12,127,571


Chapter 3 – Part IIsediment could be removed via existing accessat Lori Lane, which would not require majorinfrastructure improvements or permanenteasements. Sediment removal in the East Poolwould greatly improve water quality andstorage capacity. Other land‐based sedimentremoval actions (e.g., Sandbar East and West,Boot Unit) are likely to require establishing anin‐lake haul road and a new easement toPhoenix Lake Road (Attachment A, Sheet 4).While these design elements are feasible toimplement, they would add significant cost tothe Phase 2 project. Construction of the beachand island in the East Pool may also be acomponent of the Phase 2 project. However,this would depend on whether the East Poolwould later be used as a sediment handlingarea for water‐based dredging. If this is thecase, then a sediment handling area could beconstructed in the East Pool during the Phase 2project and the beach and island creation wouldbe completed in Phase 3.The Phase 3 project would likely encompasswater‐based sediment removal in the open lakeand construction of the West Pool‐Dredge Poolconnector channel. Dredged material wouldlikely be dewatered in the settling basin thatwas used for the 1986 dredging operations, orin the East Pool. Phase 3 operation may alsoinclude other components of the Lake Plan thatwere not completed in the Phase 1 and 2projects.This proposed phasing of project activities ispreliminary and based on currentunderstanding of project elements and lakeconditions. TUD may alter the phasing plan toaddress more pressing operational needs, suchas clearing the area around the intake tower.Finally, it is important to note that TUD intendsto pursue multiple grant funding sources toimplement various components of the PLPRP.Sediment Removal & Wetland Enhancement PlanSome funding sources may only be relevant tocertain aspects of the Lake Plan, therefore, thephasing and approach should be flexible toaccommodate the range of potential fundingopportunities.5.0 CONCLUSIONS & NEXT STEPS5.1 CONCLUSIONSThe proposed Lake Plan described in thischapter presents a comprehensive approach torestore and preserve key functions and valuesprovided by Phoenix Lake. If implemented, theLake Plan would extend the life of the reservoirwhile preserving the recreational, aestheticsand wetland values of the lake. Assuming anaverage annual deposition rate of 4,600 cy,removing more than 400,000 cy of sediment(Table 3.2‐1) would extend the life of thereservoir by more than 85 years 2 . Sedimentmanagement activities in wetland areas wouldfurther increase the life of the reservoir bytrapping sediment in locations that can beregularly managed with conventionalequipment. These activities would also improvewater quality in the lake.5.2 Next stepsIt is anticipated that the next phase of thePLPRP will include detailed engineering designand regulatory compliance. For engineeringdesign, key technical issues will include designof the sediment forebay and the new SullivanCreek channel, construction access, materialshandling procedures, and selection of reuse and2 Lake trap efficiency is a non‐linear function whereby trapefficiency is highest when lakes are deepest. As lakes fillwith sediment their trap efficiency reduces. This estimatedoes not account for non‐linear changes in reservoir trapefficiency that may result from sediment removalactivities.3.2‐16


Chapter 3 – Part IISediment Removal & Wetland Enhancement Plandisposal areas. It is anticipated that additionalsubsurface investigation will be performed torefine the depths and extents of sedimentremoval within each of the management units,and assess the suitability for equipment access(e.g., excavators, haul trucks).Multiple administrative and environmentaltasks will need to be completed for furtherdevelopment of the PLPRP. These tasks includeobtaining access and easements agreements,conducting environmental review andcompliance, obtaining necessary permits, andidentifying funding sources. Any proposedproject developed by TUD will requirecompliance with the California EnvironmentalQuality Act (CEQA). The public disclosure andoutreach activities that occur through the CEQAprocess may also provide a valuableopportunity for public comment on anyproposed actions.6.0 REFERENCESSinger, M.J. 2003. Looking back 60 years,California soils maintain overall chemicalquality. California Agriculture, Volume 57,Number 2.Wedepohl, K.H. 1995. The composition of thecontinental crust. GeochimicaCosmochimica Acta, Vol. 59, No. 7, pp.1217‐12323.2‐17


Phoenix Lake Preservation & Restoration PlanChapter 3 – Part IIAttachment A


Phoenix Lake Preservation & Restoration PlanChapter 3 – Part IIAttachment B


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Central Valley Regional Water Quality Control BoardConstituents of ConcernList of constituents of concern for leachate analysis in pre-dredgesampling 1 . The constituents listed below are the minimum suite ofconstituents of concern commonly recommended for analysis. It isthe responsibility of the discharger to accurately and completelycharacterize the material to be dredged to the best of theirprofessional knowledge, including consideration site characteristicsand any potential pollutants that may be present. Additionalconstituents may be specified for analysis, by Central Valley WaterBoard staff.ConstituentAnalytic MethodAluminum 6010B/7400Arsenic7062/6010B/7400Barium 6010B/7400Cadmium 6010B/7400Chromium – total 6010B/7400Chromium VI 7195/7196/7191Copper 6010B/7400Lead7421/6010B/7400Manganese 6010B/7400Mercury7470A/7471A (RL

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