Insights into the Effects of the Spatial Configuration of Flood Retention Ponds on Flood Frequency

Monday, 15 December 2014
Tibebu B Ayalew, Witold F Krajewski and Ricardo Mantilla, University of Iowa, Iowa City, IA, United States
As the construction of large dams for flood control purposes becomes no longer attractive due to their high cost and adverse environmental impacts, the use of spatially distributed flood retention ponds in both urban and rural settings is becoming an alternative flood management practice. However, little is known about how the spatial configuration of ponds and their storage and release capacities relative to their location in the drainage network affect the flood frequency at different locations in the catchment. In this study, we investigate this issue using a continuous simulation approach where a randomly generated rainfall time series is used to derive a hydrologic model that mimics the translation, aggregation, and attenuation of flows along the drainage network. We began by investigating how flood retention ponds that are configured either in series or in parallel affect the flood frequency using a hypothetical catchment (A=30 km2) whose drainage network is idealized using the deterministic Mandelbrot-Viseck tree. Our results show that ponds that are configured in parallel and placed at the upstream section of the basin offer a better peak flood reduction than ponds that are either configured in series along the main stem of the drainage network or a single bigger pond that is located at the outlet. The results also show that, for ponds that are configured in series, emptying the upstream dam first offers better regulation of flood peaks than emptying the downstream pond first. Moreover, our results show that, when the two ponds that are configured in series have different storage capacities, it is better to put the larger pond in the upstream section of the catchment. We further expanded the analysis to the Soap Creek catchment (A=660 km2) located in southeastern Iowa, and simulated a system of 132 flood retention ponds that have already been built across that catchment. Our results show how these ponds modify the flood frequency at different locations in the basin. Although the results show that the effect of distributed flood retention ponds on the flood frequency reduces in the downstream direction, the fact that they are distributing the flood control benefits across the catchment, as opposed to a single big reservoir located at the catchment outlet, makes them an attractive and viable flood mitigation alternative.