Feasibility of extending an artificial salmon spawning stream, Marx Creek near Hyder, Alaska.

摘要

Marx Creek, near Hyder in southeast Alaska, is a groundwater-fed, artificial salmon-spawning stream that was constructed to enhance the habitat of the atypically large chum salmon. The success of the upper Marx Creek has been limited primarily by the infiltration of silty water from the Salmon River through its flood-control dike, which results in a turbid stream environment that is not conducive to salmon spawning.;The purpose of this project was to determine whether baseflow from the groundwater system is sufficient to support a proposed 1,000-foot extension of Marx Creek. The extension would be constructed approximately 500 feet east of the existing channel, and would connect with the existing Marx Creek at a point downstream of the sediment-settling stream cell. The location of the new channel would prevent the turbid water from reaching the new channel, as it would flow into and settle out in the existing Marx Creek.;In order to accomplish this purpose, 20 monitoring wells were installed. Water level data were collected in each of the monitor wells. Slug and pumping tests were performed to determine the hydraulic conductivity at each of the well locations. Discharge measurements were also collected in July 2006 and July 2007. These data were used to create a three-dimensional groundwater flow model using Visual MODFLOW.;The model was calibrated to hydraulic head measurements and Marx Creek discharge. After achieving model calibration, three predictive simulations were run. In the first simulation the proposed extension was added to the calibrated model. The result was that baseflow to the extension significantly exceeded baseflow to Marx Creek, and that the addition of the proposed extension reduced baseflow to Marx Creek by 17%. In the second simulation, Marx Creek was removed from the model, while the proposed extension remained. The result was that discharge in the extension increased by 5%. In the third simulation a 1.06-foot drop in the model's hydraulic head was simulated, and the result was that discharge in the extension decreased by 18%. Based on these results, it is likely that baseflow to the proposed extension would be sufficient to provide habitat conducive to salmon spawning.