ASSESSMENT USING GIS AND SEDIMENT ROUTING OF THE PROPOSED REMOVAL OF BALLVILLE DAM,SANDUSKY RIVER,OHIO1

ABSTRACT: The proposed removal of Ballville Dam was assessed by (1) using a new Geographic Information Systems (GIS) based method for calculating reservoir sediment storage, (2) evaluating sediment properties and contamination from core data, and (3) assessing downstream impacts from sediment routing calculations. A 1903 (pre‐dam) map was manipulated using GIS to recreate the reservoir bathymetry at time of dam construction and used in combination with a detailed 1993 bathymetric survey to calculate sediment volumes and thickness. Reservoir sediment properties and geochemistry were determined from 14 sediment vibracores. Annual sedimentation rates varied from 1.7 to 4.3 g/cm²/yr based on Cesium‐137 (¹³⁷Cs) and Lead‐210 (²¹⁰Pb) geochronology and dated flood layers. The pore fluid geochemistry (Ba, Co, Cu, Mn) of four cores showed surficial enrichments in Cu, while Co and Mn show secondary peaks within the sediments. GIS calculations showed that a designed channel through the former reservoir able to accommodate the 10 percent Probable Maximum Flood (PMF) would require removing approximately 0.35 million m³ of sediment (27 percent of the reservoir fill), either by dredging at a cost of up to $6.3 million or by releasing fine grained sediment downstream. A sediment routing model was applied for the critical 6 km downstream using four cross sections. The sediment routing model predicts that, for flows exceeding minimum Mean Daily Flow (1924 to 1998 data), greater than 90 percent of this sediment would be transported through downstream reaches into Lake Erie (Sandusky Bay).