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american samoa - University of Hawaii at Manoa Botany Department

american samoa - University of Hawaii at Manoa Botany Department

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Chapter SixVAIPITO STREAMLOCATIONThe Vaipito Stream drainage is situ<strong>at</strong>ed upland <strong>of</strong> the inner Pago Pago Harbor and Pago PagoVillage (Figure 6-1). The stream segment investig<strong>at</strong>ed included the lower end <strong>of</strong> VaipitoStream th<strong>at</strong> extends from the Vaipito Stream mouth to about 2,725 feet upstream <strong>of</strong> theshoreline (Figure 6-2).STREAM HYDROLOGYSources <strong>of</strong> Surface Run<strong>of</strong>fThe Vaipito Stream drainage encompasses approxim<strong>at</strong>ely 1.36 square miles <strong>of</strong> land area (U.S.Army Corps <strong>of</strong> Engineers, Honolulu District, 1990). This drainage receives surface run<strong>of</strong>ffrom Gagamoe Stream, Laolao Stream, Pago Stream, Leau Stream, Vaima Stream, UtumoaStream, and Aga Stream (Figure 6-2).The Vaipito Stream drainage origin<strong>at</strong>es near the 1,200-foot elev<strong>at</strong>ion on the northwest slopes <strong>of</strong>Mt. M<strong>at</strong>afao. The main stem <strong>of</strong> Vaipito Stream flows through Pago Pago Village just east <strong>of</strong>Route 5. The stream channel passes along the northwest side <strong>of</strong> Pago Plaza and bisects PagoPark before discharging into the nearshore w<strong>at</strong>ers <strong>of</strong> inner Pago Pago Harbor.The lower stream channel th<strong>at</strong> bisects Pago Park also receives surface run<strong>of</strong>f from a secondunnamed ditch and channel th<strong>at</strong> is loc<strong>at</strong>ed on the south and east sides <strong>of</strong> Pago Pago ElementarySchool. This channel passes along the north side <strong>of</strong> a Mormon Church complex (on thesouthwest side <strong>of</strong> Route 1) and continues for about 800 feet before its confluence with the mainstem <strong>of</strong> Vaipito Stream.General Stream CharacteristicsThe lower Vaipito Stream channel segment represents a rel<strong>at</strong>ively narrow and deep channel.Exposed basalt boulders and man-made walls form the margin <strong>of</strong> the stream channel. Thestreambed typically contains a combin<strong>at</strong>ion <strong>of</strong> medium to large basalt boulders, smaller rockcobble, sand, and decomposed organic m<strong>at</strong>erial. Limited areas <strong>of</strong> the channel bottom are linedwith concrete.A considerable amount <strong>of</strong> household garbage and discarded organic m<strong>at</strong>erial was found <strong>at</strong>various points within the streambed. With increased building densities in Pago Pago, a number<strong>of</strong> landowners have also encroached their site development upon stream banks to help increasethe size <strong>of</strong> concrete driveways and vehicular parking areas.Rock walls and rock-filled gabions are loc<strong>at</strong>ed along various points <strong>of</strong> the lower streamchannel. They have apparently been installed to help prevent flood damages associ<strong>at</strong>ed withhigher stormw<strong>at</strong>er events, as well as protect properties from erosion along the stream bank.However, stream bank hardening and alter<strong>at</strong>ions <strong>of</strong> stream flow p<strong>at</strong>h have significantlyimpacted stream hydrology. Increased stream velocities, combined with alter<strong>at</strong>ions in streamflow p<strong>at</strong>h, have contributed to the failing <strong>of</strong> some gabions along Vaipito Stream.American Samoa Wetland/Stream Restor<strong>at</strong>ion and Enhancement PlanFebruary 2001, Vaipito Stream, Page 6-1

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