american samoa - University of Hawaii at Manoa Botany Department

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TABLE 9-1MEASUREMENTS FROM SELECTED STREAM CROSS SECTIONS, LEAFU STREAMMAY 1998StationChannelWidth(from top ofbank - in feet)Width ofChannelBottom(feet)ChannelDepth(feet)Other CharacteristicsL1 N/A N/A 9 9-year resident reports stream flows remainwithin stream banksL2 20 10 5 Medium rock along bottomL3 15-20 3 N/A Very grassy bottomL4 27 15 2 Rocky bottom primarily comprised of small rock.Scouring observed underneath concrete bridgeL5 N/A N/A N/A Berm adjacent to stream provides someprotection to adjacent homesL6 150 UndefinedUndefinedWetland plant indicators within undefineddrainagewayL7 N/A N/A N/A Concrete-lined channel adjoining unfinished 2-story home on man-made fill areaSource: Pedersen Planning Consultants, 1998In the vicinity of L2, significant stream bank erosion was observed along the west bank ofLeafu Stream in both May, 1998 and November, 1999. Continued bank erosion in this areawas also evident by an increase in stream channel width that had expanded from 20 feet in May1998 to 27 feet in November 1999. A former pedestrian stream crossing, which was used togain access to homes on the west side of Leafu Stream, had been washed out by higher streamflows and increased bank erosion within an 18-month period.Stream ModificationsWithin the inhabited village area, there is evidence of some stream channel modifications.These modifications generally include the past construction of short reaches of basaltic orconcrete walls, or rock-filled gabions. These structures have apparently been constructed tokeep higher stormwater flows within the stream banks or to prevent flooding on adjoiningresidential properties.Stream FlowsIn 1996, the U.S. Geological Survey estimated generally comparable rates of median streamflow for two locations along Leafu Stream (Table 9-2). These estimates were based uponcontinuous and partial gage measurements of stream flow by the U.S. Geological Survey.TABLE 9-2MEDIAN STREAM FLOW ESTIMATESLEAFU STREAMUSGS GageGage LocationStation16934000 0.9 mile upstream from stream mouth;30 feet upstream of reservoir169335000 1.3 miles NE of Leone; 900 feetupstream of village intakeSource: Wong, 1996.Stream FlowMeasurements(number)EstimatedMedian Flow(cfs)36 2.61continuous Oct,1977-Sept,1986; 5 between 1987-19902.50American Samoa Wetlands/Streams Restoration and Enhancement PlanFebruary 2001, Leafu Stream, Page 9-4
However, during and following heavier rainfall events, stream flow discharges along LeafuStream are significantly greater. For example, a maximum discharge of 400 cfs at station169335000 was recorded by USGS on December 3, 1984.Stormwater Discharges and Related Flood PotentialStormwater runoff discharges into the Leone Pala are primarily generated from heavier rainfallevents that occur within the Leafu Stream drainage. Computer modeling of the Leafu Streamdrainage by Pedersen Planning Consultants suggests potential stormwater flows range between2,350 cubic feet per second (cfs) for a 10-year storm event and 4,098 cfs for a 100-year storm(Table 9-3).TABLE 9-3STORMWATER RUNOFF DISCHARGES INTO LEONE PALA10,50, AND 100-YEAR STORM EVENTSIN CUBIC FEET PER SECOND (CFS)Location 10-Year Storm 50-Year Storm 100-Year StormLeafu Stream Mouth 2,350 3,684 4,098Source: Pedersen Planning Consultants, 1998The potential flood plain associated with a 100-year storm event in Leone Village was mappedby the Federal Emergency Management Agency (FEMA) in May 1991. Available floodinsurance rate maps prepared by FEMA suggest that residential properties along the east andwest banks of Leafu Stream could be flooded from a 100-year storm event. The 100-year floodplain extends up to 400 feet west of Leafu Stream and up to 800 feet east of the main channel.VEGETATIONNovember 1999 SurveyArt Whistler of Isle Botanica conducted a botanical survey of the lower, 300-foot segment ofLeafu Stream on November 8 and 17, 1999. Mr. Whistler was part of a three-person fieldsurvey team organized by Pedersen Planning Consultants that observed wetland vegetation,habitat for aquatic fish and invertebrates, stream hydrology, as well as land uses within andadjacent to the wetland. His observations are summarized in the following paragraphs.The vegetation along the lower 300-foot Leafu Stream is inland from the more significantwetland areas in Leone Pala that include mangrove swamp near the ocean, swamp forests,disturbed freshwater marshes, and wetland taro patches. In November 1999, the inland area,between Leafu Stream and an unnamed stream parallel to Leafu Stream, was comprised ofstream banks and transitory islands in the stream channels that were covered with herbaceousvegetation. The vegetation characterizing this inland wetland area was highly disturbed.The stream banks of this inland area were largely dominated by wetland plants such asmauutoga (commelina or Commelina diffusa), willow primrose (Ludwigia octovalvis),California grass (Brachiaria mutica), Malay ginger (Costus speciosus), and fue saina (mile-aminutevine). Also present were lesser amounts of weeds such as balsam pear (Momordicacharantia), basket grass (Oplismenus compositus), palulu (Stictocardia tiliifolia), and dissotis(Dissotis rotundifolia), and crop plants such as manioka (cassava). Trees included ulu(breadfruit), coconut, and native beach hibiscus.American Samoa Wetlands/Streams Restoration and Enhancement PlanFebruary 2001, Leafu Stream, Page 9-5
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Asili StreamAMERICAN SAMOAWETLAND/S
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American SamoaWetland/Stream Restor
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American Samoa Wetland/Stream Resto
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Figure 1-1Location of Potential Wet
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Onsite InvestigationsNovember 1999G
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Where appropriate, stream cross sec
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Chapter TwoTULA WETLANDLOCATIONTula
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Figure 2-2Tula WetlandExisting Cond
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Improved channelization of stormwat
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LAND USES IN THE VICINITY OF TULA W
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Figure 2-3Option 2: Detention of St
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Figure 2-4Option 3: Expansion of Ta
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Comparative Benefits and ImpactsPPC
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TABLE 2-4PRELIMINARY COST ESTIMATEP
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TABLE 2-5LONG-TERM RESOURCE MONITOR
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TABLE 2-6 (CONTINUED)FIELD MONITORI
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Chapter ThreeALAO WETLANDLOCATIONAl
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Figure 3-2Taufusi MarchExisting Con
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Figure 3-3FEMA 100-Year Flood Plain
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East Portion of the MarshThe impact
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WETLAND RESTORATION AND ENHANCEMENT
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The availability of new, blight-res
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Long-Term Monitoring and Site Maint
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TABLE 3-7FIELD MONITORING WORKSHEET
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Recommended monitoring stations or
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Figure 4-1Location MapAoa Village W
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No stream flow estimates are availa
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Fresh-Water SwampThe fresh-water sw
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ecome dominant if there is a nearby
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Relative Abundance and Diversity of
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Option 4: Restore Mangrove Forest U
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TABLE 4-5COMPARATIVE EVALUATIONWETL
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Long-term resource management activ
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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
Page 101 and 102: Most of lower Vaipito Stream segmen
Page 103 and 104: Red mangrove should be planted with
Page 105 and 106: TABLE 6-7PRELIMINARY COST ESTIMATEC
Page 107 and 108: TABLE 6-9LONG-TERM RESOURCE MONITOR
Page 109 and 110: TABLE 6-10 (Continued)FIELD MONITOR
Page 111 and 112: Vehicular and pedestrian access to
Page 113 and 114: Figure 7-1Location MapLeele-Papa-Ta
Page 115 and 116: Stream flow, in some cases, is cons
Page 117 and 118: Stormwater Discharges and Related F
Page 119 and 120: AQUATIC FISH AND INVERTEBRATESGener
Page 121 and 122: Opportunities and StrategiesOption
Page 123 and 124: Figure 7-3Option 2: Reduction of Er
Page 125 and 126: TABLE 7-8PRELIMINARY COST ESTIMATEP
Page 129 and 130: TABLE 7-10 (Continued)FIELD MONITOR
Page 131 and 132: More specific monitoring of stream
Page 133 and 134: Figure 8-1Location MapSauino Stream
Page 135 and 136: Stream FlowsHistorical Stream Flows
Page 137 and 138: AQUATIC FISH AND INVERTEBRATESGener
Page 139 and 140: Figure 8-3Option 1: Construction of
Page 141 and 142: FIGURE 8-5OPTION 2: PLANT NATIVE RI
Page 143 and 144: Long-Term Monitoring and Site Maint
Page 145 and 146: TABLE 8-8FIELD MONITORING WORKSHEET
Page 147 and 148: TABLE 8-8 (Continued)FIELD MONITORI
Page 149 and 150: LOCATIONChapter NineLEAFU STREAMLea
Page 151: Figure 9-2Leone Pala and 300-Foot L
Page 155 and 156: Vegetation TrendsThe lower Leafu St
Page 157 and 158: LAND USES ADJACENT TOLOWER LEAFU ST
Page 159 and 160: Option 2: Construct Basaltic Wall,
Page 161 and 162: Figure 9-5:Stabilize East Stream Ba
Page 163 and 164: TABLE 9-7PRELIMINARY COST ESTIMATEP
Page 167 and 168: TABLE 9-9 (Continued)FIELD MONITORI
Page 169 and 170: Chapter TenASILI STREAMLOCATIONAsil
Page 171 and 172: Figure 10-2Asili Stream SegmentExis
Page 173 and 174: Stormwater Discharges and Related F
Page 175 and 176: Further downstream, the stream chan
Page 177 and 178: TABLE 10-4SUMMARY OF MACROFAUNAL OR
Page 179 and 180: American Samoa Wetlands/Streams Res
Page 181 and 182: CLEAN-UP OF LOWER ASILI STREAMLABOR
Page 183 and 184: TABLE 10-9LONG-TERM RESOURCE MONITO
Page 185 and 186: TABLE 10-10 (Continued)FIELD MONITO
Page 187 and 188: Vehicular and pedestrian access to
Page 189 and 190: Figure 11-1Location MapFusi Wetland
Page 191 and 192: WETLAND VEGETATIONNovember 1999 Sur
Page 193 and 194: The lack of stream flow entering th
Page 195 and 196: Figure 11-3Option 1: Remove Solid W
Page 197 and 198: Recommended Option and Estimated Pr
Page 199 and 200: TABLE 11-6FIELD MONITORING WORKSHEE
Page 201 and 202: 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
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APPENDIX CSUMMARY OFAQUATIC MACROFA
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