Abstract: Session E  3:55 pm (Back to Session F)
Assessing Stormwater BMP’s Impact on Site Hydrology for Ecosystem and Stream Restoration

Aarin Teague, PhD
San Antonio River Authority
San Antonio, TX

Authors: Aarin Teague, Mick Bartlett, Ernest Moran, Michelle E. Garza

An important consideration of stream and ecosystem restoration is the hydrology of the watershed. Low Impact Development has been put forward as potential technique to help mitigate the impacts of urban development stressors on the watershed. This development philosophy is a group of techniques intended to mimic a site’s pre-development hydrology. This includes reducing the volume of runoff, reducing the peak flow velocity, and bringing the timing and duration of flows closer to an undeveloped state.  However, estimating the impact of the stormwater BMPs on the site’s hydrology can be challenging because of the complex physical processes that occur within the BMPs.  The San Antonio River Authority (SARA) has installed BMPs at its corporate offices as part of a demonstration project of an urban retrofit for water quality improvement.  To address the need for local data on the hydrologic impacts, representative BMPs were instrumented to continuously monitor flows in the underdrains and overflows.  Using approximately a year’s data, metrics to assess the impact of the BMPs on the site’s hydrology were calculated.  The volume reduction factor, peak flow reduction factor, and the peak delay ratio were assessed for permeable pavement and cistern to bioretention treatment trains. In addition, engineering design parameters including the effective impervious cover, curve number, and Manning’s roughness factor were estimated in order to describe BMP’s hydrologic impacts. These factors and parameters are useful in assessing the hydrology and the extent to which the BMPs are able to support stream restoration.