american samoa - University of Hawaii at Manoa Botany Department

Chapter FourAOA WETLANDLOCATIONAoa Village is located along the northeast coast of the Island of Tutuila. There is one largewetland in Aoa that comprises roughly 23.5 acres of land area (Figure 4-1). The Aoa wetlandincludes a combination of fresh-water swamp, fresh-water marsh, and swamp forest.WETLAND HYDROLOGYSources of Surface Runoff to the Aoa WetlandThe primary source of water in the wetland is surface runoff from Tapua Stream and PunaStream (Figure 4-2). Tapua Stream receives drainage from its upland tributary, Lepa Stream,and generally flows south to north through the middle of the wetland before discharging intothe nearshore waters. Puna Stream, which originates near the 400-foot contour, transportsrunoff from the west side of Olomoana Mountain through the northeast side of the wetland.Available topographic maps for Aoa Village suggest a contribution of runoff from VaitoluStream to the Aoa wetland. Field observations by PPC in November 1999 indicate that thelower channel may have been modified by local residents to:• help reduce potential flood damages to residential property; and/or,• accommodate past residential development on the southwest side of the wetland.Stream flows presently discharge directly to Aoa Bay in the Vaiaga area. PPC believes thatVaitolu Stream may have formerly discharged into Aoa wetland.A smaller portion of the runoff discharged into the wetland is also received directly from viasteeper, upland slopes on the south side of the wetland.Stream FlowsMedian Stream FlowsIn 1996, the U.S. Geological Survey published an estimated median stream flow for LepaStream (Figure 4-1). The median stream flow estimate was based upon historical stream flowmeasurements obtained from a low-flow, partial-record station between 1958 and 1975, as wellas related hydraulic modeling (Table 4-1).TABLE 4-1MEDIAN STREAM FLOW ESTIMATELEPA STREAMStreamUSGSGage StationGage LocationLepa Stream 16905000 0.5 mile upstream fromTapua Stream mouthSource: Wong, 1996Stream FlowMeasure-ments(number)EstimatedMedian Flow(cfs)22 0.11American Samoa Wetland/Stream Restoration and Enhancement PlanFebruary 2001, Aoa Wetland, Page 4-1