REACH SPECIFIC CHANNEL STABILIZATION BASED ON COMPREHENSIVE EVALUATION OF VALLEY FILL HISTORY, ALLUVIAL ARCHITECTURE AND GROUNDWATER HYDROLOGY IN A MOUNTAIN STREAM IN THE CENTRAL GREAT BASIN, NEVADA

Kingston meadow, located in the Toiyabe Range, is one of many wet meadow complexes threatened by rapid channel incision in the mountain ranges of the central Great Basin. Channel incision can lower the baselevel for groundwater discharge and de-water meadow complexes resulting in a shift from wet meadow to dry land vegetation. The Kingston meadow is located immediately up-valley of a late Holocene age side-valley alluvial fan that progrades across the main valley. Channel instability starts where the main channel gradient steepens across side-valley fans. Once channel erosion breaches the baselevel established by the side-valley fan, incision migrates upstream through the meadow. Efforts to stabilize and maintain un-incised wet meadow complexes and restore degraded meadows must focus on channel morphology, channel dynamics, alluvial architecture, and hydrogeology, all of which are inherited from events that transpired during the middle to late Holocene. To characterize the system we have installed 97 groundwater piezometers, extracted 12 deep sediment cores, used seismic profiles and ground penetrating radar, installed multiple channel cross-sections, and conducted repeated total station based topographic surveys. Complex stratigraphic and hydrogeologic circumstances produce artesian flow in the most actively degrading portion of the system. Because groundwater sapping is an important erosive process in these degrading wet meadow systems, we have ruled out several restoration possibilities such as relocating the channel or a plug and pond approach. We installed a series of nine grade control structures beginning at the side-valley fan hinge-point and extending upstream into the meadow to facilitate sediment deposition, reconstruction of the channel profile, and regrading of the water table to a higher baselevel. An active sapping zone was stabilized by the installation of fiber logs and naturally occurring rushes and sedges. Preliminary results show that the channel has aggraded tens of centimeters in channel segments upstream of the grade control structures after one period of high flow sufficient to mobilize bed material. We will continue monitoring the channel's response to the stabilization efforts.