With the increasing amount of impervious surfaces in urbanizing communities, storm water runoff has increased. Retention ponds have been implemented to ameliorate the adverse effects of this increased amount of water flow into the surrounding stream systems. Both the state and county have addressed the performance of retention ponds in a series of regulations to improve both the quality and quantity of water that is directed into these ponds.
Collecting and analyzing field data from a retention pond at Mulberry Place in James City County helped to assess the suite of performance factors. Although there was a lack of regulation-sized storms (one-year, 24-hour), the 24 hours detention time was never reached, and trends pointed towards too-high peak outflows for larger storms. Collecting and analyzing discharge data from a nearby "pristine" stream system during storm events further emphasized the inability of retention ponds to match pre-development conditions. Modeling with an engineering program was initiated as well to compare field data to design plans and predictions.
In addition, I explored the stream systems associated with retention ponds as indicators for storm water management performance. The quantity of water that passes through the retention ponds and the time it takes has a significant effect on the riparian ecosystem's health. By comparing normalized cross sectional areas for bed slope, bank slopes and width-to-depth ratio from both upstream and downstream, the differences between developed stream systems and pristine systems became apparent. A closer look into the type of sediment, amount of downstream recovery and integrated biological research would be worthwhile.
For additional documentation Cristina Lopez provided a PowerPoint Presentation entitled "The Performance of Retention Ponds and Associated Fluvial Geometry" provided here in PDF form.