american samoa - University of Hawaii at Manoa Botany Department

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A 75-foot reach of rock-filled gabions was observed along the east side of Asili Stream nearstation 9+00. Five gabion baskets were also documented in the vicinity of station 6+00 alongthe east side of the stream. Both sets of gabions were apparently constructed by residents tohelp prevent flooding from higher stream flows.Past flooding in the vicinity of station 4+00 was reported by one resident who recalled theflooding of one guest fale along the west bank of the stream (Maugaotega, 1999). Erosion ofthe stream bank was also evident in this location.Stream FlowsHistorical Stream FlowsThree stream gages have historically been established by the U.S. Geological Survey at variouspoints along Asili Stream (Table 10-1). The data gained from these stream gages provide aninsight of historical stream flows along Asili Stream.Between 1977 and 1986, a continuous-record gage (No. 16931500) was established at the 330-foot elevation. These measurements enabled USGS to calculate an estimated median flow of1.60 cubic feet per second (cfs).The same gage was operated as a partial-record site between 1987 and 1990. Extreme flowsrecorded during this period included a maximum discharge of 653 cfs on October 28, 1960 anda minimum of 0.20 cfs on August 6, 1983.Another partial record station (No. 16932500) was operated 100 feet upstream from the Route1 bridge between 1959 and 1990. Data generated from 34 measurements of stream flow wereused by USGS to estimate a median stream flow of 2.85 cfs (Wong, 1996).Various other one to two-day measurements of stream flow were made by USGS at variouspoints along Asili Stream. This data is not presented since more reliable data was obtainedfrom the three other stream gages (Table 10-1).TABLE 10-1MEDIAN STREAM FLOW ESTIMATEASILI STREAMUSGSGage StationGage Location16931500 0.8 mile upstream from streammouth at the 330-footelevation.16932000 0.5 mile upstream from theAsili Stream mouth.16932500 100 feet upstream of Route 1bridge.Source: Wong, 1996Stream FlowMeasurements(number)Continuously recordedbetween 1977-1986Estimated MedianFlow (cfs)1.6024 1.8534 2.85American Samoa Wetlands/Streams Restoration and Enhancement PlanFebruary 2001, Asili Stream, Page 10-4
Stormwater Discharges and Related Flood PotentialPedersen Planning Consultants made a hydrologic analysis of potential stormwater dischargesinto Asili Bay that could be generated from a range of storm. Through hydrologic modeling,PPC determined that potential stormwater discharges into Asili Bay can range from 620 cubicfeet per second (cfs) for a 2-year storm and about 1,606 cfs for a 100-year storm.Consequently, significant stream flows can be carried by Asili Stream for more frequent 2-yearevents, as well as less frequent 100-year storms.TABLE 10-2STORMWATER DISCHARGES FROM ASILI STREAM2,10,50, AND 100-YEAR STORM EVENTSIN CUBIC FEET PER SECOND (CFS)2-Year Storm 10-Year Storm 50-Year Storm 100-Year Storm620 938 1,468 1,606Source: Pedersen Planning Consultants, 2000In November 1999, PPC also gathered cross-sectional data along the 1,000-foot Asili Streamsegment to assess the capability of this stream segment to accommodate these stormwaterevents. Cross sections were recorded at 100-foot intervals along this stream segment.With the application of hydrologic modeling, PPC determined that potential stormwater flowsare greater than the capacity of most stream cross-sections (Table 10-3). One importantexception is the bridge culverts underneath Route 1 (station 3+00), which can accommodatestormwater flows of about 7,614 cfs. Consequently, the culverts underneath Route 1 cansupport potential flows from a 100-year storm event.TABLE 10-3CROSS-SECTIONAL ANALYSISALONG ASILI STREAM SEGMENTSlope of Stream(percent)Maximum Stream FlowThrough Cross Section(cfs)Station1+00 2.5 416.52+00 2.5 261.13+00 2.5 7,614.14+00 2.5 2,326.75+00 2.5 1,139.46+00 2.5 542.67+00 2.5 516.28+00 2.5 382.29+00 2.5 246.510+00 2.5 1,103.7Source: Pedersen Planning Consultants, 2000The potential flood plain associated with a 100-year storm event in Asili was mapped by theFederal Emergency Management Agency (FEMA) in May 1991. Available flood insuranceAmerican Samoa Wetlands/Streams Restoration and Enhancement PlanFebruary 2001, Asili Stream, Page 10-5
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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
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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
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 127 and 128: TABLE 7-9LONG-TERM RESOURCE MONITOR
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 and 152: Figure 9-2Leone Pala and 300-Foot L
Page 153 and 154: However, during and following heavi
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 165 and 166: TABLE 9-8LONG-TERM RESOURCE MONITOR
Page 167 and 168: TABLE 9-9 (Continued)FIELD MONITORI
Page 169 and 170: Chapter TenASILI STREAMLOCATIONAsil
Page 171: Figure 10-2Asili Stream SegmentExis
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
Page 203 and 204: Project ManagerRepresentatives of a
Page 205 and 206: REFERENCESBiosystems Analysis, Inc.
Page 207 and 208: APPENDIX ASUMMARY OFPLANTSOBSERVED
Page 209 and 210: Species Family EnglishNameSamoanNam
Page 213: APPENDIX CSUMMARY OFAQUATIC MACROFA
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