Design of Outlet Control Structures for Ecological Detention Ponds

Abstract

Through a simulation modeling approach, this paper seeks to modify the design of detention ponds to preserve the natural ecological flows while satisfying the requisite regulatory flow requirements. This paper will utilize an innovative ecological flow paradigm: the ecoflow statistics. The ecoflow statistics consist of nine hydrological flow statistics that have been shown to be particularly relevant to ecological quality. The statistics include annual and seasonal ecodeficits and ecosurplus, calculated using median annual and seasonal flow duration curves, and the total seasonal ecochange. A new metric called the ecodifference is defined as the weighted sum of the nine ecoflow statistics and represents the hydrologic alteration in the stream. The ecodifference in a receiving stream can be calculated using the outflow hydrograph from a detention pond hydrologic simulator. A design approach using a hydrologic model, detention pond model, and the ecodifference metric will be used to design a series of flow controls in a detention pond outlet control structure that reduces the ecological impact to the stream caused by development while meeting current design regulations. For a case study site, trial designs have demonstrated that improvements in ecological flows can be achieved while meeting design regulations. By introducing this approach for ecological detention ponds and then demonstrating its performance, this paper has potential to impact stormwater management design practice.