american samoa - University of Hawaii at Manoa Botany Department

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