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e <br />Figure 2 - Schematic diagram of falling head permeameter used to measure vertical <br />streambed hydraulic conductivity. <br />The streambed hydraulic conductivity of the South Platte River and backwater <br />slough channels at the Tamarack State Ranch Wildlife Area in eastern Colorado are <br />estimated using falling -head permeameter tests. The permeameter is a 100 cm long, <br />polyvinyl chloride (PVC) pipe with an inside diameter of 15.24 cm. The permeameter is <br />installed into the streambed with minimum disturbance to depths of 25 and 40 cm. Water <br />is added to the PVC pipe to create a hydraulic head on the sediments inside the pipe. <br />Water level measurements are taken every ten to twenty seconds until the total time for <br />the test is approximately five minutes or until measurable changes in the water level are <br />observed. The data obtained from these tests are analyzed using both the equation <br />derived from Darcy's law and the Hvorslev (1951) equation for streambed hydraulic <br />conductivity, Kb. <br />Results of the falling -head permeameter tests for the South Platte River are shown <br />in Table 1. For the case where the permeameter is installed to a depth of 25 cm, the <br />Darcy and Hvorslev equations predict an average streambed hydraulic conductivity of <br />143.7 and 168.7 m -d "1, respectively. For an installation depth of 40 cm, the Darcy and <br />Hvorslev equations predict an average streambed hydraulic conductivity of 64.3 and 71.3 <br />m -d-1, respectively. These results suggest that the deposits deeper than 0.25 cm below <br />the streambed limit groundwater /surface water fluxes in the South Platte River. Landon <br />et al. (2002) document similar results for the streambed of the Platte River in eastern <br />Nebraska. <br />4 <br />