The outer 6000 ft (sta 150+00 to 210+00) of the south jetty is degraded to or below the elevation of mean lower low water. About 4000 ft (sta 110+00 to 150+00) was rehabilitated to el +15 mean lower low water in 1966. The existing comprehensive fixed-bed model of the Grays Harbor estuary was used to determine the effects within the limitations of the model of five plans for further rehabilitation of the deteriorated portion of the south jetty and two plans for reducing the length of the existing rehabilitated portion. Model tests were conducted to determine hydraulic, salinity, shoaling, dispersion characteristics, and surface flow directions for the longest rehabilitation and reduction (plans 1 and 7, respectively). Intermediate jetty length plans 2 and 3 were subjected to hydraulic measurements and surface flow direction observations while plans 4, 5, and 6 were subjected to surface flow direction observations only. Model test results consist of tidal height, current velocity, and salinity measurements; photographs of surface current directions; shoaling patterns and rates in the entrance area; and dye dispersion characteristics. Model test results indicated that rehabilitation extension of the jetty would slightly lower the low-water elevation. Rehabilitation of the jetty would result in a general current velocity increase in the entrance navigation channel, while a reduction of the jetty length would cause a slight decrease in current velocities. Rehabilitation of the jetty tended to direct ebb currents slightly more northward seaward of the jetty ends, while a reduction in length resulted in just the opposite. Rehabilitation plans caused a slight decrease in average entrance salinities, while reduction in length resulted in a general salinity increase. Each jetty condition tested caused a slight increase in average salinities upstream from Hoquiam. It appeared that rehabilitation of the south jetty would significantly change the bottom flow predominance in the vicinity of Point Chehalis and result in a less favorable angle of attack of the flood current. Both of these effects would probably decrease the stability of Point Chehalis. The test results for a reduction in the length of the jetty indicated increased stability of Point Chehalis. Model test results indicated that either plan 1 (maximum rehabilitation) or plan 7 (maximum reduction in lenrth) would increase the possibility of scour adjacent to the south jetty. For the rehabilitated jetty, increased shoaling would occur in the existing natural channel on the north side of the entrance, while for the reduced jetty length increased shoaling would occur on the natural ridge in the center of the entrance. Dye dispersion tests for plan 1 indicated that peak concentrations for an upstream pollutant source would generally be reduced upstream of Crossover Channel but increased downstream of that location, whereas peak concentrations for an ocean pollutant source would be increased throughout the estuary._x000D_ _x000D_ NOTE: This file is large. Allow your browser several minutes to download the file.