A TECHNIQUE FOR ACCURATE URBAN RUNOFF LOAD ESTIMATION
Abstract:It has been estimated that within the next ten years Total Maximum Daily Load (TMDL) analyses will be required on over 20,000 water quality impaired waterways throughout the United States. The great majority of these waterways are receiving significant amounts of pollutants from urban and urbanizing landscapes via stormwater. One of the greatest technical challenges associated with the development of a TMDL is the ability to accurately quantify the specific amount of these stormwater pollutants that are entering a given waterway in any given year. Another challenge is the development of specific actions or activities that need to be taken to significantly reduce these pollutant loadings. Finally, perhaps the greatest technical challenge is the ability to identify the most cost effective and optimum level of effort for each activity and accurately quantify the pollutant load reductions that will result.
Pacific Water Resources, Inc. has developed and successfully implemented a load estimation procedure that can be used to quantify urban pollutant loadings and provide accurate estimates of optimum street and catchbasin cleaning practices. The load estimation procedure involves the selection and monitoring of specific pilot test areas that are representative of the various built land uses found within a watershed of interest. Instead of the costly monitoring of actual stormwater quality at each test area, the load estimation procedure calls for the intensive monitoring of the accumulation and physical/chemical characteristics of the sediment found on the streets or parking lots and within the catchbasins of a given land use. This data along with monitored rainfall is then used to calibrate a stormwater quality model called SIMPTM. Once the model has been calibrated to the various monitoring periods, an average or representative rainfall year is used to evaluate various street and catchbasin cleaning practices. Classical economic production theory and marginal cost analyses are then used to identify the optimal mix of these practices for each targeted land use. The costs associated with monitoring street dirt accumulation and catchbasin accumulations are relatively inexpensive compared to the cost of traditional stormwater runoff sampling and analyses.
The paper will specifically describe the results of this same load estimation procedure used in two different and separate projects within two Michigan watersheds. The first project was conducted in association with Hubbell Roth and Clark, Inc. (HRC) for the City of Livonia's portion of the Bell Branch and Tarabusi Creek Subwatershed of the Rouge River in southeastern Michigan. The second project was conducted in association with Tetra Tech/MPS for the City of Jackson and Jackson County's portion of the Grand River in southwestern Michigan. Both projects concluded that sweeping with high-efficiency sweepers every 15 to 30 days in combination with annual catchbasin cleaning were the optimal and most cost effective practice that could reduce total suspended solids loadings by up to 80% annually. A serious re-examination of the actual stormwater quality benefits associated with these maintenance practices is needed throughout the United States and the world.
Document Type: Research Article
Publication date: 2002-01-01
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