Hydraulic modelling for assessment of the performance of sedimentation basins downstream from extracted peatlands.

Three sedimentation basins on two different extracted peatlands were studied to determine their Trapping Efficiency (TE) using two different methods. First, TE was calculated using sediment loads estimated from turbidity measurements upstream and downstream of the basins. The second method was based on hydraulic modelling and a simplified sediment deposition model. For the first studied basin (controlled by a weir at its downstream end) TE was estimated with the second method at 85.9 % and 55.6 % for lower and higher flows, respectively. In the second peatland the studied basins were in series, there was a geotextile curtain in the middle of each basin and a weir or a double pipe culvert at the outlet. For these two basins in series, TE was estimated at 80 % for lower flows and at 34.3 % for higher flows. A hydraulic model was calibrated for the studied basins and applied to estimate the TE of different basin configurations. The results show that the role of the geotextile curtain is important in the case of short basins and for intense rainfall events. The double pipe culvert did not have a significant effect on TE, unlike the presence of a weir at the outlet, which is required to maintain high TE.