Use of SLAMM in Evaluating Best Management Practices
Once baseline water quality data reveals that beneficial uses of a stream are no longer supported, the task of evaluating alternatives for urban watershed management can be challenging for municipal planners. While working with the municipalities within the Bear Creek watershed to develop a watershed management plan, the Clinton River Watershed Council selected the Source Loading and Management Model (SLAMM) as the main instrument. A cost-effective management tool was required to assist in evaluating the effectiveness of urban best management practices (BMPs). Evaluating the suitability of the J model was difficult because we were not aware of any previous SLAMM applications in the State of Michigan. The objective became, not only to learn about and apply the model, but also to demonstrate its applicability in similar Michigan watersheds.
The Source Loading and Management Model (Pitt, 1998; Pitt and Voorhees 1995) emphasizes the use of variable quality of runoff, small storm hydrology, and particulate washoff to calculate runoff pollutant yield estimates. Unlike drainage design models, SLAMM accurately computes runoff pollutant loads and flows associated with small storm events. This is critical because most of the pollutant load is associated with the smaller, frequent runoff events.
SLAMM evaluates several control practices including detention ponds, infiltration devices, porous pavements, grass swales, catchbasin cleaning, and street cleaning. These controls can be evaluated in combinations at many source areas and at the outfalls. Furthermore, SLAMM computes the relative contributions of different source areas (e.g. roofs, streets, parking areas, landscaped areas, undeveloped areas) for each land use investigated. SLAMM requires the user to define specified impervious areas and directly connected impervious areas (DCIAs) within the model's subwatershed. DCIAs include those impervious areas that flow directly to a storm sewer, drain, channel, or waterway without flowing over any pervious surfaces. SLAMM utilizes site- specific local information including stormwater conveyance system type and condition, study period duration, rainfall depth, duration, and, and detailed land use and source area descriptions. SLAMM does not require detailed drainage system information, although the newest version of the program allows interfacing with SWMM for detailed hydraulic system evaluation
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