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USE OF ELECTRICAL RESISTIVITY PROBE WITH MODFLOW FOR SCREENING LEVEL DETERMINATION OF PARAFLUVIAL HYPORHEIC FLOW
Citation:
FAULKNER, BART, V. MURRAY, AND S. HOBSON. USE OF ELECTRICAL RESISTIVITY PROBE WITH MODFLOW FOR SCREENING LEVEL DETERMINATION OF PARAFLUVIAL HYPORHEIC FLOW. Presented at American Water Resources Association Annual Conference, Seattle, WA, November 07 - 10, 2005.
Impact/Purpose:
To inform the public
Description:
The hyporheic zone can provide significant nutrient attenuation in watersheds. Conceptual models describe the behavior of nutrients and biota for the hyporheic ecotone, but site characterization is needed to quantify these effects at the restoration reach scale (hundreds of meters). Hyporheic characterization includes quantifying the residence time distribution as well as the physical extent of the hyporheic zone within the fluvial system. Traditional methods rely on installing piezometer arrays, with data acquisition systems, at considerable time and expense. We developed and tested an inexpensive electrical resistivity probe for more rapid determination of parafluvial hyporheic flow. We tested the probe in a 125 m alluvial corridor of Big Sandy Creek, Tishomingo National Wildlife Refuge, Oklahoma (flow rate 359 L/s). A standard survey total station was used for real--time determination of capillary fringe elevation and areal location. Results were imported to a geographic information system and compared to a test area where a piezometer array was installed, surveyed, and synoptic water levels were taken. The error (due to the capillary fringe) ranged from 0 to 5 cm in coarse sandy regions, and up to 10 cm in regions containing sand mixed with muck. The Modular Three--Dimensional Finite--Difference Model (MODFLOW) was calibrated using the probe data. The particle tracking post--processor MODPATH was used to generate single--layer flow nets for the fluvial corridor. The results indicated residence times ranging from 0 to 7 days, and hyporheic flow paths up to 35 m in length within a 40 to 50 m wide fluvial corridor. These results show that for sandy alluvial streams, an electrical resistivity probe can be used for screening level determination of parafluvial hyporheic flow at scales important for stream restoration.