GOING WITH THE (STORMWATER) FLOW
A lot of the discussion around stormwater focuses on the types and amounts of pollutants — both point source and non-point sources — carried in stormwater runoff to surface water. While BMPs are primarily designed to treat or remove the pollution, they are also often designed to reduce the rate of flow of stormwater runoff entering and moving through a system. Not only do high stormwater flows cause erosion and flooding, but they carry high levels of pollutants and sediment along with them. And the heavier the flow, the heavier the pollutant load. That being said, measuring flow in pipes and open channel systems is not as straightforward as it seems. Especially when calculating low flow during first flush or early rain events, the range of accuracy measured between citizen groups and specialists depends on the project objectives and can significantly impact the calculated pollutant load carried by runoff.
Regular and systematic collection of flow data from both storm systems and receiving streams and rivers has a wide range of applications for stormwater management, including flood management in urban areas with high runoff, non-point source projects, habitat restoration efforts, and pollutant loading evaluations. Needless to say, the quality of the data generated as part of these studies is paramount to their ultimate success, and the data should include accurate flow measurements as well as an evaluation of parameters, such as turbidity and nutrients, both before and after implementing any BMPs. Doing so ensures that the BMPs have a positive impact on water quality and quantity, and also identifies whether the relationship between discharge volume and pollutant distribution/concentration changes following the implementation of a BMP. Data demonstrating the effectiveness (or lack thereof) is invaluable as we move forward to address stormwater issues on a larger scale.