A Proposal for a New Research Direction

It’s time to move in a new direction. It’s time to invest further in the development of physically based models that provide a much better understanding of the stormwater quality data we already have and the additional data we should obtain. Physically based models are mathematical programs designed to simulate physical processes that are directly related to the desired output of the model itself. For example, let’s assume that the desired output of a stormwater quality model is the storm-by-storm event mean concentration (EMC) of TSS in the runoff from an urban site of interest. A physically based model would attempt to simulate the accumulation of particulate material on the site and the washoff of this sourcematerial by the site’s estimated stormwater runoff. Both the accumulation component and the washoff component would be physical processes included in the model.

Typical pollutant loading models are based on various land use types: single and multi-family residential, commercial, industrial, freeways, and open space. Unfortunately, this format is not particularly useful, as it is not tied directly to the specific BMPs under consideration and likely to be implemented. We suggest an alternative format based on pollutant source areas that comprise a site like streets, parking lots, roofs, landscaped areas of various descriptions, and other activity types that relate directly to certain pollutant sources like construction sites or gas stations. Such a format allows a direct tie to BMPs and various LID treatments.

The end user of the proposed tool would most likely be the development or redevelopment engineer responsible for managing stormwater quality and quantity leaving a site. This tool could be used to model and implement design standards specified by the community for structural BMPs including on-site detention and low impact development (LID) techniques, which are likely to be required. At this scale, the development engineer wants to maximize the cost effectiveness of several LIDs (e.g. amended soils, porous pavements, rain gardens or green roofs) as a way to reduce detention volume and improve water quality. As a result, this tool must be able to explicitly simulate the integrated performance of these LID techniques on a storm-to-storm basis over a long time period so the hydrologic response of the site under the user defined LID design conditions are specifically known.

The stormwater management tool we envision will also have the ability to explicitly model the pollutant reduction effectiveness of both structural and non-structural BMPs on a storm-to-storm basis over a long time period. The proposed Pollution Reduction Spreadsheet Tool’s final outputs were to be estimates of specific pollutant loadings and concentrations entering receiving waters along with the marginal costs of pollutant removal using various BMPs. Some components already exist in other established models and would only need to be integrated together.