Optimization technique to retrofit series of detention basins in Sycamore Run, Gahanna, Ohio

The stormwater study objective is to analyze the existing stormwater runoff conditions affecting Sycamore Run watershed. The study modeled the existing stormwater system to determine under what conditions (e.g., return period, rainfall amount, intensity, etc.) surcharge develops and flooding occurs. The study analyzed the impact of various rainfall events and provided recommendations for remediation projects to street and yard flooding.

Sycamore Run urban watershed includes 8 existing detention basins. These were designed and constructed over the last 30 years utilizing different design codes and regulations. The upstream land uses of many of these basins have changed dramatically. The setup of the control structures of these detention basins is no longer achieving its intended purpose to control/reduce stormwater flow in Sycamore Run. The stormwater study concluded that the control structure of these basins can be altered to minimize stormwater flow rate in Sycamore Run flow and hence reduce flooding and stream erosion.

In this paper, the PCSWMM Genetic Algorithm (GA) routine is utilized to calibrate the watershed model to observed flow depth and high water marks at key locations in Sycamore Run. Calibration parameters were drainage areas’ imperviousness and catchments’ width.

The calibrated model was then used as input to another set of GA analyses to investigate the impact of changing detention basins’ control structure setup. The GA routine is utilized to maximize in-line storage of Sycamore Run detention basins by systematically adjusting the setup of the control structures of these detention basins. The sizes and inverts of the detention basins control structures are taken as the decision variables. The desired flow rates at Sycamore Run during different design storms were used as observed values and the GA routine was forced to adjust the detention control structures set up (decision values) to meet the desired flow requirement.