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November 13 @ 12:00 PM - 1:00 PM - Burton D. Morgan Center for Entrepreneurship (MRGN), room 129
Marty Frisbee, Assistant professor of hydrogeology and applied geology in the Department of Earth, Atmospheric and Planetary Sciences at Purdue University will speak on Thursday, Nov 13, 2014 at noon in the Burton D. Morgan Center for Entrepreneurship (MRGN), room 129. Sandwiches will be provided.
His lecture is entitled: Groundwater/Surface Water Interactions in Complex Geology: Insights and Frustrations from the El RitoWatershed, New Mexico.
A growing body of research has shown that the common and persistent perception that surface water systems have little to no interaction with deep groundwater is not always valid. As an example, my recent research indicates that groundwater/surface water interactions are very complex in the El Rito watershed of northern New Mexico; yet, the watershed does not fully conform to my 3D-watershed conceptual model. The watershed itself is geologically complex with east-dipping Tertiary conglomerates (prominent in the headwaters but absent near the outlet) overlying an assortment of west-dipping Mesozoic and older shales and sandstones. Longitudinal trends of stream discharge are very intriguing (and frustrating) and indicate that the El Rito watershed can be broken into four distinct hydrogeological zones: 1) perennial streamflow in the headwaters maintained by springs and groundwater discharge, 2) losing conditions downstream of the headwaters, 3) a small, persistent 500 m gaining stretch in the mid-reach, and 4) losing conditions from the mid-reaches to the outlet. I hypothesize that interbasin groundwater flow (IGF) controls the spatial occurrence of springs and losing/gaining transitions in the watershed. In order to test this hypothesis, I mentored several undergraduate researchers from 2011 to 2014 in mapping the landscape placement of springs and their relation to certain geologic units, collecting spring and stream waters samples for geochemical and radiocarbon age-dating analyses, measuring longitudinal patterns of stream discharge, measuring stream temperature profiles (especially around suspected zones of groundwater upwelling), and analyzing spring and stream water samples for tritium and Radon-222. These data provide strong support for IGF controls on spring generation in zone 1 and on the gaining-to-losing transition in zone 2. The groundwater connection is strongest where the Tertiary conglomerates are present. Once these units thin or become absent, that connection is lost (e.g., zone 2). In comparison, very diffuse and spatially discontinuous zones of groundwater upwelling in zone 3 were identified by temperature anomalies, spikes in Radon-222, and decreases in tritium concentrations. These data indicate that groundwater from an adjacent watershed to the east likely upwells into El Rito creek where groundwater flowpaths in the Mesozoic layers have intercepted fault zones. This research highlights the need to quantify the role of stratigraphy and structure on streamflow generation in large watersheds and a need to quantify what is really implied by the “watershed” response, especially in regions where interbasin flow is a consideration. Furthermore, these data suggest that sometimes stream gauges are liars, hiding more complex process information than they actually reveal.
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