american samoa - University of Hawaii at Manoa Botany Department

Stream/Pago Stream confluence. In a related reconnaissance report, the U.S. Army Corps ofEngineers concluded:“The greatest flood problem occurs in the downstream area, approximately 600 feet above themain highway (Route 1) down to the mouth. While the outlet has ample flood carryingcapacity, the existing bankfull capacity of Vaipito Stream in the land-filled area (Pago Park) is1,100 cfs, a discharge slightly greater than a 2-year flood” (U.S. Army Corps of Engineers,1988).While flooding typically occurs on the lands within Pago Park, flooding in this area typicallygenerates limited to no property damage since few structures are located within the Park. Inrecent years, however, more governmental buildings have been constructed along Route 1 andthe west margin of the Park. The blockage of culverts along Route 1 frequently generatesflooding within and around these buildings following more frequent storm events.Erosion poses a problem upstream of Route 1, particularly along bends of the stream. “Streambanks exposed to the erosive forces of the stream are provided minimal protection with a thinconcrete blanket” (U.S. Army Corps of Engineers, 1988).Stream CapacitiesThe U.S. Army Corps of Engineersalso modeled stream capacities aspart of its 1988 reconnaissancereport for Vaipito Stream (Table 6-3).VEGETATIONNovember 1999 SurveyTABLE 6-3ESTIMATED VAIPITO STREAM CAPACITIESStation LocationCapacity (cfs)0+00 to 7+00 1,6007+00 to 18+00 1,10018+00 to 28+00 1,20028+00 to 38+00 70038+00 to 54+00 870Source: U.S. Army Corps of Engineers, 1988Art Whistler of Isle Botanica conducted a botanical survey of the Vaipito Stream segment onNovember 4, 1999. Mr. Whistler was part of a three-person field survey team organized byPedersen Planning 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.Vaipito Stream Mouth and Confluence with Unnamed StreamThe stream banks, between the Vaipito Stream mouth and its confluence with the unnameddrainage from Pago Pago Elementary School, were dominated by a mixture of alien plantspecies. Some of these species were typical of a wetland; others were indicative of an uplandenvironment. Most of the relatively flat stream bank areas were characterized by salt grass(Paspalum vaginatum), Fimbristylis cymosa, and carpet grass (Axonopus compressus), as wellas scattered concentrations of fue moa (beach morning-glory).Roughly 30 other alien herbaceous plants were noted along the stream banks just upstream ofthe Vaipito Stream mouth. Along the south bank of the stream, there were thickets of wildtamarind (Leucaena leucocephala), scattered fau (beach hibiscus) trees, patches of elephantgrass (Pennisetum purpureum), beggar’s tick (Bidens alba), beach morning-glory, andAmerican Samoa Wetland/Stream Restoration and Enhancement PlanFebruary 2001, Vaipito Stream, Page 6-5