ANALYSIS OF SEDIMENT TRANSPORT ASSOCIATED WITH LOW-HEAD DAMS

A mathematical sediment-transport model, SEDMOD, was used to simulate stream flows and sediment transport in a river channel with four low-head dams on the Kalamazoo River in Michigan. The steady-state 1-dimensional model uses time-varying hydrographs to compute the resultant scour and fill at any given location in the river reach. Different modeling scenarios were generated to assess sediment transport under varying hydraulic conditions. The model was calibrated using root mean square error (RMSE) as an objective function for measuring the goodness-of-fit between the model-computed suspended-sediment transport rates and observed suspended-sediment data. Calibrated model results show close agreement between simulated and measured values of suspended sediments.Analyses of the model results show that the Kalamazoo River sediment-transport mechanism is in a dynamic-equilibrium state. Analysis of the model results shows that significant sediment erosion from the study reach occurred at flow rates higher than 55 m3/sec. And sediment deposition mainly occurred during low-to-average flow conditions (monthly mean flows between 25.49 m3/sec and 50.97 m3/sec), following a high flow event until the system reached equilibrium.Because the dams in the study reach have low heads and no control gates, the 1947 flood flow simulations show no significant difference between the transport rates during the “dam in” and “dam out” scenarios. Therefore, during high flow conditions, approximately the same magnitudes of velocities are generated in the backwater sections in both scenarios, which produce the same impact on sediment-erosion rates. It is important to note that the “dam in” and “dam out” scenarios simulations are run for only 60 days, which takes into account only the instantaneous changes in sediment erosion and deposition rates during that time period. Over an extended period of time, it is expected that more erosion will occur if the dams are removed from the study reach than under the existing conditions. Based on the simulations, removal of dams would further lower the head in all the channels producing higher velocities even during low-to-average flow conditions, which would result in accelerated erosion rates throughout the study reach.