DO REACH-SCALE GEOMORPHICALLY DEFINED PROCESS ZONES PREDICT SENSITIVITY OF CHANNEL SYSTEMS AND HYDROLOGIC PROCESSES IN THE MOUNTAINS OF THE CENTRAL GREAT BASIN?

Riparian corridors in the mountains of the central Great Basin, host to ecologically valuable meadow complexes, are largely controlled and threatened by channel systems. Previous research has established the geologic, geomorphic, and hydrogeologic settings and processes of these riparian systems, but mostly basin-scale approaches show poor correlation to riparian meadow locations and degrees of channel incision. The purpose of this study is to determine if a hierarchical approach based on geomorphic process zones explains 1) within and between basin channel characteristics, 2) sensitivity of stream systems, and 3) hydrologic processes.

Channel-slope systems in 7 basins, representing different geomorphic states, were mapped for 9 major units based on 1) valley form (hollow or valley), 2) presence or absence of a channel, and 3) material type (alluvium, colluvium, bedrock). In addition, non-channelized segments, common on alluvial/colluvial fans, were mapped because of the importance to sediment and hydrologic connectivity. Topographic cross sections, slopes, grain size, lithology, and hydrologic traits were determined for dozens of sites in all basins to characterize each map unit. Two subbasins were instrumented with hydrologic monitoring equipment to directly assess hydrologic processes and connectivity in relation to process zones.

Work is preliminary, but in basins analyzed unincised hollows and valleys are the most common process zone units by frequency and cumulative length. Percent connectedness of a basin is the area of the basin/subbasin with continuous channels that can contribute sediment and surface water to axial channels. At basin scale, connectedness varies from 74 to 83 % with higher percents in basins that have more axial channel incision. Groundwater and surface water traits show a general, but not exact, correspondence to process zones. Non-connected segments, pending channel formation by big events, block transport of surface water and sediment decreasing the likelihood of downstream channel change, but promote groundwater recharge important to sustaining riparian ecosystems. Further work will complete spatial and structural analysis of map units, and develop models that can, at least conceptually, predict reach and basin scale response for different magnitude events