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The Michigan Water Withdrawal Assessment process demonstrates an effective science-policy process with user-friendly decision tools developed to support it.  Hamilton and Seelbach (2011), Ruswick et al. (2010) and Steinman et al. (2011) provide detailed overviews of the entire scientific and policy development.
A series of interstate compacts and Michigan water management laws initially spawned the process. Annex 2001 to the Great Lakes Charter, ratified in 2008 in the Great Lakes Compact, stipulates that signatory states may cause no significant adverse individual or cumulative impacts on the quantity and quality of the Waters and Water-Dependent Natural Resources of the Great Lakes Basin. Signatory states further commit to:
• establish programs to manage and regulate new or increased withdrawals;
• implement effective mechanisms for decision making and dispute resolution;
• develop mechanisms by which individual and cumulative impacts of water withdrawals can be assessed; and
• improve the sources and applications of scientific information regarding Waters of the Great Lakes Basin and the impacts of withdrawals from various locations and water sources on the ecosystems.
An “Adverse Resource Impact” impairs the ability of a stream to support characteristic fish populations, seen as biological indicators of the overall health of rivers and streams. Michigan’s 2006 water law committed the state to create an integrated assessment model to determine the potential for any proposed water withdrawal to adversely impact the state’s waters and water-dependent resources.
An Advisory Council composed of industry, advocacy, NGO, agency, and academic stakeholders was convened and given a 1-year timeline and strong bipartisan support to recommend a process to the Michigan legislature to carry out this mandate. The Council developed and operated under Guiding Principles, to which its success is largely attributed. These Principles focused Council members on their common interests, regardless of their other differences. The process recommended by the Council (Michigan Groundwater Conservation Advisory Council 2007) ultimately was adopted into state law (2008 Public Act 189). The Michigan Department of Environmental Quality was the primary implementing agency. 
Stream segments were first delineated to provide the foundation for subsequent analysis and management of environmental flows. River reaches were grouped into segments believed to have relatively homogeneous hydrology, geomorphology, hydraulics, water quality, water temperature, and biological attributes with fish assemblages that are distinct from neighboring segments (Brenden et al. 2008).
The hydrologic foundation is a database of the median daily flow for the month of lowest summer flow (typically August) for each stream segment.  This “Index Flow” was chosen because it represents the most ecologically stressful period of the year. The amount of water that can be withdrawn is expressed as a percent of Index Flow, as suggested by Richter (2009). Multiple linear regressions using landscape and climate characteristics (aquifer transmissivity, forest cover, average annual precipitation, and soil permeability) were used to estimate the Index Flow for all ungaged stream segments (Hamilton et al. 2008).
In Michigan, groundwater discharge plays a significant role in determining fish species assemblage. During the summer low-flow period, groundwater discharge provides most of river flow, and regulates temperature and dissolved oxygen levels. Groundwater withdrawals by pumping wells reduce natural groundwater discharge to rivers. To account for groundwater withdrawals, a computer model estimates streamflow depletion  for  a proposed withdrawal based on well location, depth, aquifer and riverbed characteristics, and the timing and quantity of withdrawal (Reeves 2008, Reeves et al. 2009).
Stream segments were classified according to catchment size and thermal regime, which are the dominant variables shown to influence fish assemblages in Michigan (Lyons et al. 2009, Wehrly et al. 2003, Zorn et al. 2008). This classification yielded 11 river types (Brenden et al. 2008, Seelbach et al. 2006). For each of the 11 river types, Zorn et al. (2009) modeled fish response curves that relate population and density changes in fish communities to percentage reductions in Index Flow. Michigan’s ecological response curves are unique because they summarize in a single model the response of the entire fish community to flow alteration in a given river type.
Prospective water users employ an online Water Withdrawal Assessment Tool (WWAT; Michigan Department of Environmental Quality 2009) to determine the level of risk associated with their proposed withdrawals. Users enter the location, timing, quantity, and if relevant, the screen depth of their proposed groundwater or surface water withdrawals. Using the hydrologic foundation and groundwater model, the WWAT calculates flow depletion of a stream segment during summer low flow due to the proposed withdrawal, added to the cumulative withdrawals from upstream segments. Using the stream types and fish response curves, the WWAT associates the depletion with its risk level. If the risk level is low, then the withdrawal may be registered online with no further analysis. If the risk level is high, meaning the withdrawal would likely cause an Adverse Resource Impact, then site-specific review by Department of Environmental Quality staff is required, using local flow and fish data and expert opinion instead of the less accurate statewide model. After site review, the withdrawal will be registered, registered with modifications, or rejected.  By associating different policy actions with different levels of risk, Michigan compensates for uncertainties in the models used to quantify Adverse Resource Impact.
Michigan’s process expedites water withdrawal registrations, focuses limited agency staff time on proposed withdrawals that pose the most risk, and steers future withdrawals toward least-sensitive rivers -- all while maintaining flow variability and supplying off-stream water needs.
Read more about Michigan’s Water Withdrawal Assessment Process in A Practical Guide to Environmental Flows for Policy and Planning.