In light of innovation, this spotlight is for the 3rd place winner for the 2017 Best BMP Retrofit BUBBA, Anacostia River Watershed Smart Integrated Stormwater Management. As a part of the larger 64,000 square mile Potomac River Watershed, this 15 acre-feet wet pond collects and retains stormwater from 440 acres at Sligo Creek, a tributary to the Anacostia River. Before the retrofit, the US Environmental Protection Agency’s (EPA) “pollution diet” called for a 25 percent reduction in nitrogen, 24 percent reduction in phosphorus, and 20 percent reduction in sediment. Additionally, the wet pond did not meet the State of Maryland’s requirement to treat one inch of rainfall runoff from impervious surfaces in the drainage area.
MWCOG was awarded a grant to collaborate on a multi-jurisdictional project funded by the National Fish and Wildlife Foundation (NFWF) to demonstrate the use of smart, integrated stormwater management systems. The project team selected University Boulevard Wet Pond in Montgomery County as the top wet pond enhancement candidate to install Continuous Monitoring and Adaptive Control (CMAC). The objectives of this retrofit were to accelerate the adoption of municipal green infrastructure, measure the increased sediment and removal benefits, demonstrate cost-saving benefits, and use a dynamic feedback system. The process of addressing the objectives included installing a control panel, solar supply package, actuated valves, and level sensors.
After being installed and monitored for over 12 months, the grant projected has helped support several regional water quality initiatives. Some initiatives include the Chesapeake Bay Total Maximum Daily Load (TMDL) and the Chesapeake Bay Stewardship Fund (CBSF) Conservation Objectives. Furthermore, the project has paved the way to accelerating the pace of achieving the County’s water quality goals.
Through monitoring, the project demonstrated water quality improvements through the use of adaptive controls. Data from May 2016 showed that the CMAC retrofit prepared the site for a total of 16.4 million gallons of runoff and reduced the total wet weather runoff volume downstream of the pond by 67%. Further, the 47-hour average retention time of all water discharged from the pond during the month doubled the retention period of the pond pre-retrofit while 81% of all flow volume discharged met a 24-hour retention time, a design criterion for new construction set forth by the MDE. CMAC represents a new and unique approach to managing stormwater and has emerged as an alternative to passive stormwater management facilities.
In summary, the innovative design allowed for less costly wet pond enhancement retrofits by eliminating the need for excavation to increase the water quality volume. The forecast-based active control of the outlet valve also allowed for combining the water quality volume and channel protection volumes specified in traditional wet pond design, resulting in a smaller total pond volume. These controls effectively redesigned the project site to optimize performance for a wide range of actual rainfall events instead of compromising performance to target static criteria.
