Environmental flow tools used to frame new water management policy in Michigan

In fulfilling the state’s commitments under the Great Lakes—St Lawrence River Water Resources Compact, Michigan recently passed a series of new water management laws.  These require science-based assessment of proposed large-quantity water withdrawals, to prevent any additional adverse impact to aquatic resources.  A state advisory council assembled a series of ecological tools into an assessment framework.  First, fish habitat suitability models were summarized so as to describe assemblage-level declines in response to incremental reductions in river flow.  A unique set of these flow-fish response curves was developed for each of eleven ecological river types found across Michigan.  Second, a tiered series of water withdrawal policy zones were overlain onto the flow-fish response curves, guided by the concept of the biological condition gradient.  The zone series describes an increasing gradient of risk of resource impact, paralleled by an increasing gradient of required engagement and responsibility by the withdrawer.  The final zone indicates very high risk of resource impact and withdrawals are not allowed.  Third, a statewide ecological river segment classification was completed, providing the mapping framework for statewide application of the assessment process.  An internet-based screening tool was implemented so that for any river segment in Michigan, one can readily determine the ecological type, the estimated summer index flow, the flow-fish response, the associated policy details, and the policy determination for a proposed nearby withdrawal.  Oversight of the development process by the advisory council assured that the underlying science was not strongly debated during the final crafting of the new state laws; instead political debate and negotiations were focused appropriately on balancing social values, ultimately leading to passage of the laws.