Transport of Dredged Sediments after Disposal Operation in Lake Erie

A dredged material disposal operation was monitored on a location in Lake Erie 8 km offshore Ashtabula, Ohio, June to November, 1975. Some 200 sediment cores were collected in the periods before and after dredging and analyzed for the grain-size distribution of the sediments. Two current meters and a wave sensor moored nearby monitored the movement of the water masses. The sediments were dredged in the Ashtabula River and Harbor and discharged at a pre-designated location by a hopper dredge. A control site was established nearby. These sediments proved to be very similar to the ones from the lake bottom at the disposal site and the control site. Because of this similarity, it was extremely difficult to distinguish between the dredged material and the lake sediments without tagging the dredged material. Plotting the percentage of sand, silt and clay in several replicates collected at one site before and after disposal of dredged material allowed distinction between local and dredged sediments. Sediment transport could approximately be determined by the use of a modified computer program (SEDMOT), which calculates and plots progressive vector diagrams based on pre-assigned critical erosion and deposition velocities for specific grain sizes. The results showed that silt-sized sediments could have been transported over distances as large as 20 km. The main direction of transport was northeast and southwest, following the bottom topography. OHIO J. SCI. 81(1): 2, 1981 A dredged material disposal operation was monitored on a location 8 km offshore Ashtabula, Ohio, in Lake Erie. One of the objectives of the program was to study the movement of dredged sediments. In order to achieve this objective, the grain size population of the sediments from the Ashtabula Harbor and River, which was to be dredged, and of the lake bottom at the disposal site was analyzed. After dredged material was disposed, we again collected lake bottom sediments at the disposal site. With the aide of current meters and a wave sensor, we attempted to interpret the resulting differences in sediment distribution and to determine possible directions and distance of transportation. Many attempts have been made to determine the amount and direction of sediment transport in water environments similar to that in Lake Erie. Manuscript received 10 March 1980 and in revised form 24 July 1980 (#80-9). Three basic methods are generally used to estimate the sediment transport: 1. analyzing sediment grain-size distributions by use of moment statistics over several time intervals and estimating the direction of transport by comparing changes in the geographic distribution patterns (Pezetta 1975) 2. estimating the direction of transport by using measured water current values (McClennen and Kramer