american samoa - University of Hawaii at Manoa Botany Department

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Stormwater Discharges and Related Flood PotentialPedersen Planning Consultants made a hydrologic analysis of Vailoa Stream in 1998 todetermine the potential amount of stormwater that could be discharged into the Tula wetland.TABLE 2-1POTENTIAL STORMWATER DISCHARGES INTO TULA WETLAND2,10,50, AND 100-YEAR STORM EVENTSIN CUBIC FEET PER SECOND (CFS)Location 2-Year Storm 10-Year Storm 50-Year Storm 100-Year StormAll Surface Runoff 244 465 735 944Source: Pedersen Planning Consultants, 1998Through hydraulic modeling, PPC determined that potential stormwater discharges alongVailoa stream could range from 244 cubic feet per second (cfs) for a 2-year storm and about944 cfs for a 100-year storm.The areal extent of flood potential associated with an 11-year storm event was mapped by theFederal Emergency Management Agency (FEMA) in May 1991. When this information iscorrelated with digital building location data from the American Samoa GIS, it is clear that a100-year flood event would clearly impact most of the inhabited village area.In January 2000, representatives of the American Samoa Coastal Management Programobserved flooding in the vicinity of the Tula wetland and along the lower Vailoa Streamdrainage. This flooding was generated from a stormwater event that occurred January 20through January 22, 2000. Climatological data from the National Weather Service station atPago Pago International Airport recorded 6.41 inches of rainfall during this period. Availablerecords from NOAA’s Cape Matatula station near Tula Village indicate that the station madeno measurements during the January 20-22 period.American Samoa Wetland/Stream Restoration and Enhancement PlanFebruary 2001, Tula Wetland, Page 2-4
Improved channelization of stormwater flows is needed to help reduce potential damages toresidential and commercial property in the village. Following higher rainfall events, surfacestormwater flows upland of the village has repeatedly spread over much of the upland portionof the inhabited village area. As a result, various homes in the upland village area have beenflooded. The capacity of the lower portion of Vailoa Stream is inadequate to accommodatelarger stormwater flows. The lower stream channel has likely been altered over the years toaccommodate gradual residential expansion in the upland village area. In addition, the presentblockage of the lower stream channel increases the areal extent of potential flooding andproperty damage resulting from a 100-year storm and less severe storm events.Construction of a second upland channel would help alleviate present flooding in the uplandarea and, at the same time, enable the transport of stormwater flows to the wetland. Onedesirable use of the Tula wetland would be stormwater detention. Restoration of this wetlandfunction would help reduce the amount of sedimentation that can be generated from VailoaStream. Stormwater detention would also permit the treatment and recharge of stormwater intothe fringe of the basal aquifer.WETLAND VEGETATIONNovember 1999 SurveyArt Whistler of Isle Botanica conducted a botanical survey of the Tula wetland on November 2and 17, 1999. Mr. Whistler was part of a three-person field survey team organized by PedersenPlanning Consultants that observed wetland vegetation, habitat for aquatic fish andinvertebrates, stream hydrology, as well as land uses within and adjacent to the wetland. Hisobservations are summarized in the following paragraphs.West Side of Vailoa StreamVegetation observed within the Tula wetland along the west side of Vailoa Stream was notrepresentative of a wetland. Vegetation along the stream banks represented a mixture of typicalwetland or wetland margin plants such as Coix lacryma-jobi sanasana (Job’s tears), Paspalumconjugatum vao lima (T-grass), and more typical upland species such as Nephrolepis hirsutulavao tuaniu (sword fern). A few Hibiscus tiliaceus fau (beach hibiscus) and Barringtoniasamoensis falaga were also evident along the stream banks.Southwest of the Primary Shoreline RoadwayA fresh-water swamp dominated by beach hibiscus and a trough of highly disturbed marsh wasobserved southwest of a recent fill area. The fill area is immediately adjacent to the southwestside of the primary shoreline roadway.The highly disturbed marsh is situated in the northwest part of the wetland. The marsh isdominated by T-grass and somewhat less amounts of California grass and mauutoga(commelina). Considerably less amounts of weeds, such as Kyllinga nemoralis, tropicalcupgrass, Phyllanthus amarus, and three-flowered beggarweed were also evident in the marsh.All of the plants observed in this area represented introduced plant species. The only nativeherb recorded during the survey was selesele (Mariscus javanicus) that comprised only a fewclumps at the south end of the marsh.American Samoa Wetland/Stream Restoration and Enhancement PlanFebruary 2001, Tula Wetland, Page 2-5
Page 1 and 2: Asili StreamAMERICAN SAMOAWETLAND/S
Page 3 and 4: American SamoaWetland/Stream Restor
Page 5 and 6: American Samoa Wetland/Stream Resto
Page 11 and 12: Figure 1-1Location of Potential Wet
Page 13 and 14: Onsite InvestigationsNovember 1999G
Page 15 and 16: Where appropriate, stream cross sec
Page 17 and 18: Chapter TwoTULA WETLANDLOCATIONTula
Page 19: Figure 2-2Tula WetlandExisting Cond
Page 23 and 24: LAND USES IN THE VICINITY OF TULA W
Page 25 and 26: Figure 2-3Option 2: Detention of St
Page 27 and 28: Figure 2-4Option 3: Expansion of Ta
Page 29 and 30: Comparative Benefits and ImpactsPPC
Page 31 and 32: TABLE 2-4PRELIMINARY COST ESTIMATEP
Page 33 and 34: TABLE 2-5LONG-TERM RESOURCE MONITOR
Page 35 and 36: TABLE 2-6 (CONTINUED)FIELD MONITORI
Page 37 and 38: Chapter ThreeALAO WETLANDLOCATIONAl
Page 39 and 40: Figure 3-2Taufusi MarchExisting Con
Page 41 and 42: Figure 3-3FEMA 100-Year Flood Plain
Page 43 and 44: East Portion of the MarshThe impact
Page 45 and 46: WETLAND RESTORATION AND ENHANCEMENT
Page 47 and 48: The availability of new, blight-res
Page 49 and 50: Long-Term Monitoring and Site Maint
Page 51 and 52: TABLE 3-7FIELD MONITORING WORKSHEET
Page 53 and 54: Recommended monitoring stations or
Page 55 and 56: Figure 4-1Location MapAoa Village W
Page 57 and 58: No stream flow estimates are availa
Page 59 and 60: Fresh-Water SwampThe fresh-water sw
Page 61 and 62: ecome dominant if there is a nearby
Page 63 and 64: Relative Abundance and Diversity of
Page 65 and 66: Option 4: Restore Mangrove Forest U
Page 67 and 68: TABLE 4-5COMPARATIVE EVALUATIONWETL
Page 69 and 70: Long-term resource management activ
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TABLE 4-9FIELD MONITORING WORKSHEET
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• begin at the Tapua Stream mouth
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Figure 5-1Location MapSoutheast Wet
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Tufu Stream and two stream branches
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Mr. Whistler was part of a three-pe
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InvertebratesCrustacean densities w
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FIGURE 5-3OPTION 1: RESTORE RIPARIA
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TABLE 5-4COMPARATIVE EVALUATIONWETL
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Long term monitoring of the Vatia w
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More specific monitoring of stream
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Figure 6-1Location MapVaipito Strea
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Stream FlowsHistorical Stream Flows
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California grass (Brachiaria mutica
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FIGURE 6-3FISH AND INVERTEBRATE SUR
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Most of lower Vaipito Stream segmen
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Red mangrove should be planted with
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TABLE 6-7PRELIMINARY COST ESTIMATEC
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TABLE 6-9LONG-TERM RESOURCE MONITOR
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TABLE 6-10 (Continued)FIELD MONITOR
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Vehicular and pedestrian access to
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Figure 7-1Location MapLeele-Papa-Ta
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Stream flow, in some cases, is cons
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Stormwater Discharges and Related F
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AQUATIC FISH AND INVERTEBRATESGener
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Opportunities and StrategiesOption
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Figure 7-3Option 2: Reduction of Er
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TABLE 7-8PRELIMINARY COST ESTIMATEP
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TABLE 7-10 (Continued)FIELD MONITOR
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More specific monitoring of stream
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Figure 8-1Location MapSauino Stream
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Stream FlowsHistorical Stream Flows
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AQUATIC FISH AND INVERTEBRATESGener
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Figure 8-3Option 1: Construction of
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FIGURE 8-5OPTION 2: PLANT NATIVE RI
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Long-Term Monitoring and Site Maint
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TABLE 8-8 (Continued)FIELD MONITORI
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LOCATIONChapter NineLEAFU STREAMLea
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Figure 9-2Leone Pala and 300-Foot L
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However, during and following heavi
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Vegetation TrendsThe lower Leafu St
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LAND USES ADJACENT TOLOWER LEAFU ST
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Option 2: Construct Basaltic Wall,
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Figure 9-5:Stabilize East Stream Ba
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TABLE 9-7PRELIMINARY COST ESTIMATEP
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Page 167 and 168:
TABLE 9-9 (Continued)FIELD MONITORI
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Chapter TenASILI STREAMLOCATIONAsil
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Figure 10-2Asili Stream SegmentExis
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Stormwater Discharges and Related F
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Further downstream, the stream chan
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TABLE 10-4SUMMARY OF MACROFAUNAL OR
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American Samoa Wetlands/Streams Res
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CLEAN-UP OF LOWER ASILI STREAMLABOR
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TABLE 10-9LONG-TERM RESOURCE MONITO
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TABLE 10-10 (Continued)FIELD MONITO
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Vehicular and pedestrian access to
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Figure 11-1Location MapFusi Wetland
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WETLAND VEGETATIONNovember 1999 Sur
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The lack of stream flow entering th
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Figure 11-3Option 1: Remove Solid W
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Recommended Option and Estimated Pr
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TABLE 11-6FIELD MONITORING WORKSHEE
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Any future monitoring stations or s
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Project ManagerRepresentatives of a
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REFERENCESBiosystems Analysis, Inc.
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APPENDIX ASUMMARY OFPLANTSOBSERVED
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Species Family EnglishNameSamoanNam
Page 213:
APPENDIX CSUMMARY OFAQUATIC MACROFA
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