Simulation of Hydraulic Conditions and Observed and Potential Geomorphic Changes in a Reconfigured Reach of Muddy Creek, North-Central Colorado, 2001-2008

摘要

Muddy Creek near Kremmling, Colorado, is a regulated, meandering, gravel-bed stream that has been monitored for geomorphic change since 2001. One reach of the creek was reconfigured using natural-channel design methods in 2003, providing an opportunity to compare hydraulics in this reach with those in a nearby, unaltered control reach. Streamflow in Muddy Creek has been regulated by Wolford Mountain Reservoir since 1995, but reservoir releases in 2006 and 2008 resulted in out-of-bank floods. The Muddy Creek monitoring program was conducted by the U.S. Geological Survey from 2001 to 2008 in cooperation with the Colorado River Water Conservation District, and the streamflow modeling and analysis were conducted in 2008 in cooperation with the Colorado River Water Conservation District and the Colorado Water Conservation Board. Minor changes in channel geometry were measured at monitored cross sections in the control reach between 2001 and 2008 and in the reconfigured reach between 2003 and 2008. Geomorphic changes were limited to lateral erosion in a meander bend and lateral erosion of an alluvial fan that formed a vertical scarp in the control reach. Some excavated streambed locations in the reconfigured reach have aggraded to their former elevations, and gravel on alluvial bars might have become better sorted and winnowed of sand-size sediment. Hydraulic conditions in the reconfigured and control reaches were simulated using the U.S. Geological Survey MD-SWMS framework and FaSTMECH computational models. Model topography was created from onsite surveys, and model simulations were calibrated with surveyed water-surface elevations and the corresponding discharges for low, medium, high, and out-of-bank flood discharges. The simulations produced 2-dimensional estimates for depth, velocity, bed shear stress, and sedimenttransport strength for each discharge. High bed shear stresses generally occurred in areas of the greatest depth and velocity, such as in meander bends (where depths were greater) and in steeper gradient areas (where velocities were greater).