DEVELOPING TOOLS FOR ASSESSING THE IMPACTS OF WATER WITHDRAWALS IN THE GREAT LAKES-ST. LAWRENCE BASIN

The Governors and Premiers of the Great Lakes States and Provinces have long recognized the need for a regional water management system for the Great Lakes. In 1985 they signed the Great Lakes Charter, which outlines principles for managing this expansive but finite resource. A later amendment to the Charter called the Great Lakes Charter Annex, or Annex 2001, outlined a framework for a set of guiding principles for reviewing proposals for new and increased water withdrawals. The principles include conservation measures, no significant adverse individual or cumulative impacts, and an improvement to the waters and water-dependent natural resources of the Great Lakes. The amendment also directed that a decision support system be developed to ensure access to, and use of, best available information.The States and Provinces, through the Council of Great Lakes Governors, are currently engaged in a three-year process of turning Annex 2001 into regional water management standards. The Great Lakes Protection Fund (GLPF) is supporting this effort by funding several projects that build technical tools, or test various decision-making processes. This paper describes one of these projects, which involves the development of a linked modeling framework to assess the ecological impacts of withdrawals and diversions in a Great Lakes tributary.The application of mathematical models provides the potential for evaluating water withdrawal impacts at the full range of spatial and temporal scales to address management issues. However, existing models generally address only part of the overall problem, such as watershed hydrologic response, channel hydraulics, sediment transport, water quality, or ecological effects. No existing model by itself directly links a water withdrawal to ecological endpoints, or addresses the broad range of potential ecological responses resulting from water withdrawal scenarios.To address the need for this type of decision support tool, we developed a prototype modeling framework that permits direct evaluation of how hydrologic changes associated with water withdrawals affect important ecological aspects of a river-based watershed. The modeling framework links the Hydrologic Simulation Program – FORTRAN (HSPF) model to a series of habitat-based ecosystem submodels developed based on existing stand-alone ecosystem models. The prototype model was fieldtested on the Muskegon River watershed, located in northwest lower Michigan. Water withdrawals in this watershed can potentially impact flow regime and water temperature in mainstem and tributary reaches, thus affecting the habitat of brown trout and other important species in the system.An important objective of this work was to explore issues and challenges to developing a model of this type. Challenges we encountered related primarily to data processing and availability. The large size of the Muskegon River watershed required that we collect and synthesize a large volume of data and information, a time-consuming process. Furthermore, certain types of data and information, such as information related to ecological effects and processes were very limited or non-existent. We also explored the applicability of this type of model to other watersheds. This model has broad potential applicability, but site-specific modifications to the model will always be necessary, particularly for the ecosystem components, due to the complexity of the watershed as well as data availability.The ultimate objective of our work is to develop a user-friendly, linked model framework that can be applied to a wide range of Great Lakes basin systems. This prototype model represents a first step toward meeting that objective. Follow up work will build on this project by refining, further developing, and applying this modeling framework to a wider range of river systems within the basin. This will also include the development of a decision support interface for the model suite to support effective development, assessment, and comparison of different water withdrawal scenarios by decision-makers.The utility of the technical tools developed through this and other efforts will be considered for use by parties responsible for making decisions concerning new water withdrawal applications in the context of the Great Lakes Charter Annex. It is envisioned that these approaches as implemented in a specific watershed could be used as an adaptive management tool by incorporating results of ongoing monitoring, thereby providing a synthesis tool and a methodology for assessing cumulative impacts of multiple flow modifications. In addition, models for individual watersheds could potentially be linked to form a larger Great Lakes Basin assessment tool.