Flow Routing in Two Watersheds in the Rocky Mountains, Colorado

Meixner, T W
Department of Hydrology and Water Resources University of Arizona Tucson, AZ 85721-0011 United States

Bales, R C
Department of Hydrology and Water Resources University of Arizona Tucson, AZ 85721-0011 United States

Mark W Williams
Department of Geography and Institute of Arctic and Alpine Research University of Colorado, Boulder

Campbell, D H
USGS-WRD, Federal Center

Baron, J S
USGS-BRD NREL Colorado State University, Fort Collins, CO 80523


We evaluated the sensitivity of water quality to flow routing in two high-elevation Rocky Mountain catchments, the Andrews Creek subcatchment (part of the Loch Vale watershed, Rocky Mountain National Park) and the Green Lakes watershed (part of the Niwot Ridge LTER), with quite different relative flow paths through soil and talus. Both sites had comparable data sets from 1994 and 1996, including high-resolution spatial data and high frequency time series of hydrology, geochemistry and meteorology. We used the Alpine Hydrochemical Model (AHM) to evaluate the relative importance of soil and talus geochemical processes on stream chemical composition. The model of each watershed consisted of three terrestrial subunits; soil, talus and rock with the routing between the subunits determined by spatial land cover data. For both watersheds 1994 data were used for model calibration and 1996 data for evaluation. In Andrews Creek where all snowmelt, including that on soil, flows through talus enroute to the stream, stream composition was only sensitive to parameters describing chemical reactions in talus. The opposite was true for Green Lakes, where all snowmelt contacts soil enroute to the stream. Field measurements at both watersheds indicate that talus pore waters exert a significant control on stream chemistry. The contradiction of modeling results with field measurements suggests that it will be necessary to quantify the hydrologic and chemical properties of landcover classes (e.g. soil and talus) in order to understand flow routing within a watershed.