Converting Dry Ponds to Wet Ponds without Excavation: Forecast-Based Real Time Outlet Control Offers a Least-Cost Retrofit Strategy

Both traditional stormwater best management practices (BMPs) and green infrastructure systems have almost entirely been designed as passive systems governed by a fixed control structure designed to achieve a target water quality and/or quantity objective. Due to the advances in low cost, internet accessible controller systems and wired and wireless communications, real-time and dynamic controls of BMPs are now viable, cost- effective options for new construction as well as retrofits. These technologies allow BMPs to be monitored and controlled in real time via the internet. This active water management solution is particularly powerful in urban areas where space is not available for more traditional stormwater management practices and budgets may not allow for more costly retrofit methods on older, nonfunctional facilities. The first real-time control dry pond retrofit for nutrient reduction in the Chesapeake Bay watershed was deployed in November 2015. The installation results in approximately 2 acre-feet (2,500 cubic meters) of new water quality treatment volume at the facility and provides 48 hour residence time independent of storm size. The total area treated is 60 acres including 19 impervious acres. The innovative retrofit approach cost approximately ten times less than a traditional, excavation approach to achieve the same treatment volume.