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Michigan State University
215 Farrall Hall
East Lansing, MI 48824
Phone: 517-355-4720
Fax: 517-432-2892
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Estimating Groundwater Recharge across Michigan
Abundant freshwater is one of the most precious resources in the State of Michigan. Recent legislation has been passed to protect surface waters from the impact of excessive groundwater pumping. Excessive pumping of shallow groundwater aquifers can result in decreased baseflow to streams and rivers and can have a negative impact on sensitive aquatic habitat. The source of baseflow in creeks and streams is from groundwater recharge which results from rainfall that infiltrates into the soil and percolates down past the root zone and eventually makes its way as baseflow into a stream. One of the characteristics of high quality trout streams is high baseflow, which cools the water and provides good habitat for trout. There are many human activities that can adversely affect stream baseflow such as increased groundwater pumping in a shallow aquifer near a stream. Another example is a land use change in the groundwater contributing area that would reduce the amount of rainfall that eventually percolates into the groundwater, (for example, the conversion of forested land into a parking lot).
In 2004, the Great Lakes Protection Fund awarded a grant to MSU through the Institute of Water Research to develop a system of water trading credits to help offset the impact of groundwater pumping on stream habitat. To accomplish this work a team of policy researchers along with three modeling teams (surface water, groundwater, and fisheries modeling) were assembled to develop this system as a tool to aid in decision making in the installation of high capacity wells. The surface water modeling team consists of William Northcott and Steve Miller, Department of Biosystems and Agricultural Engineering and Dr. Jeffrey Andresen, Department of Geography. The goal of the surface water modeling team was to develop a multi-dimensional spatial database of groundwater recharge values for the State of Michigan . To accomplish this, the Soil and Water Assessment Tool (SWAT), a continuous, daily time-step model was used to model the long-term water balance and recharge across several parameters. These variables include climatic zone, soil type, land use class, and land management practice.
To validate the suitability of using SWAT to estimate groundwater recharge over a spatially diverse landscape we applied the model to a portion of the Kalamazoo River watershed. In our study we simulated the hydrology of the Kalamazoo from its headwaters to the USGS gaging station at Fennville, MI a drainage area of about 1,600 km 2 . We chose the Kalamazoo due to its large size, diverse rainfall patterns, land use, and soils as well as a number of long-term USGS gaging stations within the watershed to compare our modeling results. Figure 1 show the delineation of the Kalamazoo river basin based on the USGS gaging stations used in this study. The watershed map is shaded with the USGS estimated groundwater recharge.
For each subbasin in the watershed, the hydrology of the watershed, including stream base flow was simulated with the SWAT model using daily climate data from seven weather stations located within and around that watershed for the years from 1975 - 2000. The model accounts for hydrologic differences due to climate, soil type and land cover. As a basis to evaluate the model, observed daily stream flow data for each subbasin was collected from the USGS. Daily stream base flow was estimated from the daily time series of data for each subbasin using a digital recursive filter approach. For each gaging station average annual baseflow (recharge) was calculated. Also as a comparison, the model was evaluated with a USGS regression technique for estimating baseflow. In this case, the USGS estimate was in the form of a one mi 2 grid of recharge values. For each subbasin, the contributing grid estimates were averaged. The results of all of the calculations are shown in
Table 1.
Gaging Station
USGS Measured Annual Recharge
(mm)
USGS Regression Equation Estimate (mm)
SWAT Estimate
(mm)
Kalamazoo at Fennville
281.3
294.4
269.6
Kalamazoo at Comstaock
265.5
265.7
253.7
Augusta Creek
318.4
326.5
340.61
Kalamazoo at Battle Creek
240.3
248.6
228.13
Battle Creek
236.0
231.5
235.7
Wananadoga Creek
180.5
264.9
227.6
Kalamazoo at Marshall
194.0
245.0
173.0
Table 1. Comparison of estimated recharge to measured recharge at gages within the Kalamazoo River .
The results of this study have shown that by using a model such as SWAT, we can accurately estimate groundwater recharge over large areas. By using a dynamic watershed scale model we have the tools to estimate what the impact that such events as climate change or urbanization will have on the groundwater resources of the State.
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