HR: 15:25h
AN: H13K-07    [Abstracts]
TI: Spatial and Temporal Variability in Streambed Fluxes in an Agricultural Watershed, Leary Weber Ditch, IN
AU: * Essaid, H I
EM: hiessaid@usgs.gov
AF: USGS, 345 Middlefield Rd., MS496, Menlo Park, CA 94025 United States
AU: Wilson, J T
EM: jtwilson@usgs.gov
AF: USGS, 5957 Lakeside Blvd., Indianapolis, IN 46278 United States
AU: Baker, N T
EM: ntbaker
AF: USGS, 5957 Lakeside Blvd., Indianapolis, IN 46278 United States
AB: The Agricultural Chemicals Topical Study (ACT) of the U.S. Geological Survey's National Water Quality Assessment Program (NAWQA) is studying multiple settings with various agricultural management practices to assess the fate of agricultural contaminants. As part of this effort, surface water - ground water (SW-GW) interactions have been studied in the streambed of the Leary Weber Ditch, a 7.2 km² subwatershed within the Sugar Creek Basin, IN. This is an intensively farmed corn and soybean region with poorly permeable surface and subsurface materials, predominantly till with interbedded lenses of outwash. Three methods were used to determine the streambed SW-GW exchanges: point measurements using seepage meters; streamflow measurements at upstream and downstream sites; and one- and two-dimensional modeling of water and heat flow. Hydraulic heads and water temperatures were monitored continuously within piezometer clusters along two transects near the mouth of the subwatershed. Simulation of water and heat flow was used to help interpret the head and temperature observations, and deduce the SW-GW fluxes. SW-GW exchange was influenced by physical heterogeneity below the streambed, specifically the distribution of clay deposits. Water exchange was low through sections of the streambed underlain by clay, with higher flow through the streambed occurring where clay was absent. Model estimates of flux magnitude and direction varied throughout the year. In general, flux was upward through the streambed during the wet part of the year (October-June) with the exception of flood events. Flood events resulted in rapid short-lived reversal of flow direction causing water to flow downward into the streambed. During the dry season (July-September), surface-water was periodically lost to ground water resulting in drying of the ditch. Seepage meter and streamflow measurements support the temperature-based flux estimates. These findings are being used to improve the understanding of the fate of agricultural chemicals in these environments.
DE: 1829 Groundwater hydrology
DE: 1830 Groundwater/surface water interaction
DE: 1847 Modeling
SC: Hydrology [H]
MN: Fall Meeting 2005