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Potter, Kenneth W.; Olson, David (Researcher); Bube, Jon; Ferdinand, Roman; Bradbury, K. R. / Groundwater hydrology of an agricultural watershed
[DNR-109] (1995)

7. Future work,   pp. 33-34 PDF (624.4 KB)

Page 33

      discharge area, such as the Garfoot Creek watershed. The flow paths
      associated the former are deeper and much longer than those associated with
      the later. Hence it is this recharge that primarily contributes to deep
      groundwater, our most reliable groundwater source. And because of its
      longer flow paths, the contribution of this recharge to baseflow decreases
      much less rapidly during dry periods. In fact, during extreme droughts, this
      water may constitute virtually all of the baseflow. Hence it is essential
      that management strategies for protecting groundwater recharge focus on
      regional recharge areas.
           The extent to which gullies contribute to groundwater contamination in
      the Driftless Area is not known. The gulley we monitored was capable of
      infiltrating significant amounts of runoff. But over a three year period,
      there were only four events which produced runoff in the gulley. Three of
      these were snowmelt events. Typically, snowmelt runoff is not likely to be
      highly contaminated, unless manure was spread during the winter. The fourth
      event was the 10 cm rainfall event on July 5, 1993. This event produced
      about 1 cm of runoff from the agricultural upland, at least a third of which
      infiltrated into the gulley. We did not get a sample of this runoff for
      laboratory analysis. However, the U. S. Geological Survey (Holmstrom et
      a/.,1994) did sample Garfoot Creek on that day, finding measurable
      concentrations of atrazine (0.9 tg/il), cyanazine (6.1 4g/I), metolachlor (6.0
      ig/Il), and 2,4-D  (0.54 jig/l). If other gullies  in  the  region  also  infiltrate
      runoff, then gullies could be a significant source of groundwater
      contamination by agricultural chemicals.
      7. FUTURE WORK
           As a result of this study we have improved our understanding of the
      hydrology of the Black Earth Creek and S,-gar River watersheds, as well as of
      the Driftless Area in general. However, there remain some issues which are
      critical to wise management of the water resources of the region. In
      addition, some of the calculations in this report should be refined as
      additional data become available.
           It is clear that significant infiltration occurs in our instrumented gully.
       It is not clear where that water goes and the degree to which it
hI     contaminates groundwater. More importantly, it is critical to determine how

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