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It's all about Balance: Using a watershed model to evaluate costs, benefits and tradeoffs for Monponsett Ponds watershed
Citation:
Detenbeck, N., V. Zoltay, I. Morin, A. Morrison, T. Garrigan, J. Leclair, R. Abele, AND M. Tenbrink. It's all about Balance: Using a watershed model to evaluate costs, benefits and tradeoffs for Monponsett Ponds watershed. Monponsett Ponds Watershed Management, Kingston, MA, September 10, 2015.
Impact/Purpose:
This is a seminar presented at the invitation of the Halifax Board of Health to citizens in the Monponsett Pond watershed and surrounding communities as part of a series of three related seminars. The presentation describes the application of EPA's Watershed Management Optimization Support Tool v2 (WMOSTv2) to the water quantity and water quality problems in the Monponsett Ponds watershed.
Description:
As part of an EPA Region 1 RARE project, EPA Region 1 reached out to towns in the Taunton River watershed to identify those interested in testing new version of EPA watershed management tool (WMOST version 2)and found Halifax, MA in need of assistance in dealing with a suite of water-quantity and quality issues in the Monponsett Ponds Watershed. Issues include loss of a natural flow regime in Stump Brook with potential impacts on fish migration and sensitive downstream ecosystems, water diversions, flooding, impaired recreational uses, blue-green algal blooms, bacteria counts, and beach closures. EPA applied a new version of WMOSTv2 which provides stakeholders with the opportunity to identify goals, evaluate integrated management practices across stormwater, drinking water, wastewater and land conservation programs, and ultimately identify the most cost-effective solutions. WMOSTv2 is essentially a water accounting tool, evaluating the effects of variations in weather, soils, land-use, and water extractions and returns in affecting the water balance. In collaboration with the Monponsett Ponds Watershed Workgroup, EPA evaluated scenarios using an historic weather period covering both wet and dry years, evaluating ranges in pond level (with tradeoffs between water supply and flooding), targets for a more natural flow regime, and the timing and magnitude of diversions from Monponsett Ponds to Silver Lake. Management practices considered included water conservation (fixing leaks and reducing demand), alternative water sources (short-range interbasin transfers, desalination plant sources), green infrastructure stormwater best management practices, and aquifer storage and recharge. WMOSTv2 identified areas in the MP watershed for least cost GI BMP placement as zones with sand and gravel soils with high-density residential or commercial land-use. Using the FEMA HAZUS tool, EPA quantified the potential flooding costs associated with higher ranges in pond levels and tradeoffs between water supply, flooding, and associated water quality problems (e.g., potential septic tank failures). Four example potential management scenarios were presented to examine the potential for achieving the 25th percentile of historic unimpacted streamflows. In most successful scenarios meeting goals, GI stormwater BMPs were selected as one of the least cost management solutions. Next steps include the need to consider the effect of management actions on water quality as well as quantity, evaluate a regional integrated water management solution, and application of finer scale tools to guide site-specific implementation.