american samoa - University of Hawaii at Manoa Botany Department

flow velocities have apparently generated excessive erosion along the east bank of Papa Streamand littered the stream bed with considerable amounts of rock and debris.Due to the erosive nature of soils along the stream bank, aggressive bank stabilization practicesshould be used to help improve stream hydrology and reduce the amount of future stream bankerosion. While various construction options are available, it recommended that the east bank ofPapa Stream be armored with basaltic rock and grouted with a concrete slurry along theupstream and downstream sides of the Tauese Stream discharge (Figure 7-3). This approachwill enable the construction of a strong bank structure without increasing the velocity ofdownstream stream flows.Option 3: Restore Stream Path Upstream of Project AreaOption 3 would design and construct stream improvements that would:• restore the former single, stream path some 700 to 800 feet upstream of station 11+80;• somewhat reduce stream velocities downstream of the basaltic wall that has generatedsignificant downstream bank erosion;• reduce further downstream bank erosion along east and west banks of Papa Stream; and,• provide potential opportunities for planting wetland trees such as ifi along the 100-150-footlength of the stream bank that has been impacted by stream modification.ASEPA/ASDOC would need to retain a professional engineer to design conceptual,preliminary, and final construction drawings, as well as preliminary cost estimates, for thisstream improvement project. Once funds are secured for this project, a building contractorwould be selected for construction of the proposed design.Comparative Benefits and ImpactsPPC’s evaluation of the three alternate restoration and enhancement strategies is summarized inTable 7-6. Option 1 provides somewhat greater benefits to wetland vegetation and fish andinvertebrate habitat for a reasonable cost. Option 2 provides some needed improvementsbetween station 5+00 and 6+00 that would help reduce bank erosion and potential floodingalong a portion of lower Papa Stream.Option 3 would address a significant bank erosion and stream hydrology upstream of theproject area. This project would provide some benefits to wetland vegetation, as well as fishand invertebrate habitat. However, the potential significant cost associated with this projectmakes this project less desirable despite its need.TABLE 7-6COMPARATIVE EVALUATIONWETLAND RESTORATION AND ENHANCEMENT OPPORTUNITIESLOWER PAPA STREAMOption Project Residential Subsistence Fish & Wetland/ StreamCost Land Uses Agriculture Invertebrate Riparian BankFlood Hazards& PropertyDamageHabitat Vegetation Stability1 LC LB NBC MB SB NBC LB2 MC NBC NBC MB LB NBC MB3 SC MB NBC LB LB NBC LBNotes: Potential project benefits were rated by PPC as follows:SB Significant project benefitsLC Limited undesirable consequencesMB Moderate project benefitsMC Moderate undesirable consequencesLB Limited project benefitsSC Significant undesirable project impactsNBC No anticipated project benefits orundesirable consequencesSource: Pedersen Planning Consultants, 2000American Samoa Wetland/Stream Restoration and Enhancement PlanFebruary 2001, Papa Stream, Page 7-11