Bioretention Design and Performance in Johnson County, KS

摘要

The Johnson County Stormwater Management Program provides funding for a number of research and development projects that implement structural BMPs to improve runoff water quality prior to discharge into local waterways. Since 2006, this program has helped cities in Johnson County install multiple bioretention systems to treat runoff from roads or parking lots. Due to their geographical clustering in northeastern Kansas, these bioretention systems have all been subjected to very similar weather patterns and storm events during this time. For this project, we are carrying out a comparative assessment study of identically designed bioretention systems installed at two locations in Overland Park, KS to determine how system design and operation interact with site-specific variables to impact effluent water quality. Available water quality data from 2008-2010 were analyzed to determine cell performance with respect to removal of suspended solids, Zn, Cu and nitrogen and phosphorus species. In both cases, influent runoff is primarily from paved parking lots, with substantial storm to storm variation in pollutant concentrations. Both systems remove suspended solids and Zn, but there is minimal effect on Cu concentrations, which are already quite low in the influent runoff. Nitrogen and phosphorus concentrations, however, increase as the runoff passes through the bioretention cells. Some of this increase is likely due to the breakdown of organic materials mixed into the cell soil matrix. At one site, however, leaf fall and other detritus appear to result in much higher effluent nutrient concentrations. Further work will assess the relative performance of these systems in high and low volume storm events and suggest improvements that should be incorporated in bioretention construction in order to meet regional specific challenges associated with Great Plains weather and climate patterns and native vegetation.