Physical and conceptual modeling of sedimentation characteristics in stormwater detention basins
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To minimize the non-point source pollution from roadway surface, TxDOT (Texas Department of Transportation) launched a project for designing a small footprint non-proprietary detention basin, which consists of pipes and box culvert sections with specialized inlet and outlet system. The project was done with a team from Texas A&M University who is responsible for prototype experiments. To conduct the project of our part, two approaches were taken: one is using a conceptual model and the other is using a physical model. The conceptual model was developed to estimate particle removal efficiency of the rectangular detention basin for the treatment of stormwater runoff by extending ideal horizontal flow reactor theory under the condition in which water level is varied. The physical model was built in 1/5 scale of the prototype to measure its particle removal performance and verify the conceptual model. Several experimental runs were conducted using the physical model with steady inflow conditions, but various inflow rates, durations, and suspended solid concentrations (SSC). viii Measured time series outflow SSC and particle removal efficiency conformed closely to the calculated results from the conceptual model although the measured particle removal efficiency in the physical model was always few percent better than the predicted result using the conceptual model. Physical model similitude problem was studied using the developed conceptual model. The results show that small scale physical model results can be scaled using Hazen number scaling. The measured outflow SSC showed an interesting behavior. During the filling period, outflow SSC was almost constant and the value was proportional to the overflow velocity. During the emptying period, outflow SSC decreased with time as if particles have a settling velocity of water level dropping in most of the cases. A simpler empirical model to estimate the particle removal efficiency was also developed using these findings.