Effect of Impoundment and Diversion on the Sediment Budget and Nearshore Sedimentation of Southern Indian Lake

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Abstract
Shoreline erosion added an annual average of 4 × 106 t of mineral sediment per year to Southern Indian Lake (postimpoundment area, 2391 km2) during the first 3 yr of impoundment. This erosion increased sedimentary input to the lake by a factor of 20. The lake retained 90% of this eroded material within its basin, and 80–90% of the retained material was deposited nearshore. Despite the production of extremely fine constituent particle sizes, eroding shorelines generated predominantly large clay aggregates, initially transported offshore as bed load. During bed load transport, abrasion of clay aggregates produced fine particles that became suspended. Over 80% of the suspended load is lost to outflows from the lake because the suspended load is primarily fine silt and clay-sized particles, most of which do not settle even under winter ice cover. The extensive nearshore clay aggregate deposits are temporary, and net deposition in these areas will change to net erosion when input of sediment from eroding shorelines ceases. The effects of shoreline erosion on the lake's sediment regime will persist for decades.

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