Ground water discharge to the Great Lakes around the Lower Peninsula of Michigan is primarily from recharge in riparian basins and proximal upland areas that are especially important to the northern half of the Lake Michigan shoreline. A steady-state finite-difference model was developed to simulate ground water flow in four regional aquifers in Michigan's Lower Peninsula: the Glaciofluvial, Saginaw, Parma-Bayport, and Marshall aquifers interlayered with the Till/"red beds," Saginaw, and Michigan confining units, respectively. The model domain was laterally bound by a continuous specified-head boundary, formed from lakes Michigan, Huron, St. Clair, and Erie, with the St. Clair and Detroit River connecting channels. The model was developed to quantify regional ground water flow in the aquifer systems using independently determined recharge estimates. According to the flow model, local stream stages and discharges account for 95% of the overall model water budget; only 50% enters the lakes directly from the ground water system. Direct ground water discharge to the Great Lakes' shorelines was calculated at 36 m3/sec, accounting for 5% of the overall model water budget. Lowland areas contribute far less ground water discharge to the Great Lakes than upland areas. The model indicates that Saginaw Bay receives only approximately 1.13 m3/sec ground water; the southern half of the Lake Michigan shoreline receives only approximately 2.83 m3/sec. In contrast, the northern half of the Lake Michigan shoreline receives more than 17 m3/sec from upland areas.
__ 6. Available surface-water data._________________ 7. Average precipitation and runoff.______________ 8. Hy drographs of daily mean discharge _________________ 9. Map showing areal variation in runoff._____________ 10. Duration curves of daily discharge, Middle Branch Escanaba River near Ishpeming-_________________ 11. Low-flow frequency curves, Escanaba River basin.__._-12. Frequency-mass curve and draft-storage lines, Middle Branch Escanaba River.__________________________ 13. Graphs showing draft-storage-frequency relations.-14. Regional draft-storage curves, central and western Upper Peninsula._-________-_-__-_________ 30 15-18. Graphs showing: 15. Low flow and potential water supply, Middle Branch Escanaba River__________________ 31 16. Low flow and potential water supply' , East Branch Escanaba River and Goose Lake Outlet-___________-___._______________ 17. Low flow and potential water supply, Michigamme River___________________________ 18. Magnitude and frequency of annual floods. _ _ _ _ 19. Map showing frequency, discharge, depth, and elevation of floods.
At the request of Congress, the U.S. Geological Survey (USGS) is assessing the availability and use of the Nation's water resources to gain a clearer understanding of the status of our water resources and the land-use, water-use, and natural climatic trends that affect them. The goal of the National Assessment of Water Availability and Use Program is to improve our ability to forecast water availability for future economic and environmental uses. Simply put, the assessment will help characterize how much water we have now, how water availability is changing, and how much water we can expect to have in the future. Currently (2005), the assessment is focused on the Great Lakes Basin (fig.1) to determine the best methods to evaluate water resources and to develop strategies for delivering information about water availability and use. Other water-resources regions will be added to the assessment as evaluation methods improve and as funding permits. Golf-course irrigation well and water distribution system (photograph by N. Grannemann, U.S. Geological Survey).
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