Flood Management Process
Within the WRE, jurisdictions should identify recurrent flooding areas in local watersheds and carefully evaluate whether climate change and planned development will exacerbate those conditions; if so, changes to the land use plan or other measures should occur. Local governments should determine if historical flooding problems exist and denote them in the WRE. The WRE should include recommendations for quantity management requirements in those areas, including over management or retrofitting in some areas if flooding problems are severe.
Also, the WRE should determine and maintain the capacity of the stormwater system to convey runoff as growth continues. As a high-level first attempt, local governments should map known and potential future flooding problems characterized by reason: floodplain encroachment; conveyance system under-sized, etc., and then prioritize these areas for more detailed study. Based on the study results, local governments could establish watershed-specific water quantity management standards for new development in these watersheds. In addition, the studies could identify where upgrades to an undersized stormwater system are needed or flood warning systems or floodplain acquisitions should be pursued. Local governments should consider downzoning or the establishment of additional requirements for conveyance system upgrades as part of new development projects.
The WRE should identify areas above and below drinking water reservoir dams and other high, significant, and low hazard dams and should consider restrictions in these areas regarding new development unless dam safety storm capacity issues are adequate or expected to be addressed as part of a development project.
Maryland's Comprehensive Flood Control and Watershed Management Program requires comprehensive watershed management plans for the implementation of flood control measures in watersheds that are prone to flooding. Counties should include or reference these plans as part of their WRE and then implement the flood control strategies. The WRE should include a recommendation that all growth strategies should be consistent with comprehensive watershed plans, studies, or capital projects implemented pursuant to Maryland’s Comprehensive Flood Management Grant Program. MDE, Planning, and MDA are required to provide technical aid in development of these watershed plans. The plans also are a requirement for Flood Control and Watershed Management grants administered by the Water Quality Finance Administration. These plans are also key to addressing expected changes that are occurring due to climate change.
For new development, Maryland’s minimum control requirements for stormwater (COMAR 26.17.02.06.A, County and Municipal Requirements) require local approving authorities to manage more than the minimum stormwater requirements if historical flooding problems exist and/or if interjurisdictional watersheds are designated as flood hazard watersheds (consult the following online tools from the Maryland Resiliency Partnership HERE to identify flood hazard watersheds). Similar language is in the Maryland Stormwater Design manual, standard #6, which is incorporated by reference (COMAR 26.17.02.01-1) and states “control of the two-year and ten-year frequency storm events is required if the local authority determines that additional stormwater management is necessary because historical flooding problems exist and downstream floodplain development and conveyance system design cannot be controlled. In addition, safe conveyance of the 100-year storm event through stormwater management practices shall be provided.”