Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2004
Publication Date: 8/26/2005
Citation: McNamara, J.P., Chandler, D., Seyfried, M.S., and Achet, S., Soil moisture states, lateral flow, and streamflow generation in a semi-arid, snowmelt-driven catchment, Hydrological Processes 19, 4023-4038, 2005. Interpretive Summary: Recent advances in snowmelt modeling are enabling us to accurately predict the amount and timing of snowmelt water delivered to the soil. For this information to become truly useful, we need to understand how and when that water passes through the soil to streams, where it is a critical resource of wildlife (especially fish), irrigation and power generation. We found that, on a local scale, there are specific thresholds that snowmelt inputs must overcome for snowmelt to generate streamflow. This finding is important because it will improve our ability to predict the amount and timing of snowmelt water delivery to streams and ultimately rivers. The impact is primarily on a scientific level in that it will lead to improved models used by those responsible for managing water resources.
Technical Abstract: Hydraulic connectivity on hillslopes and the existence of preferred soil moisture states in a catchment are important controls on runoff generation. In this study we investigate the relationships between soil moisture patterns, lateral hillslope flow, and streamflow generation in a semi-arid, snowmelt driven catchment. We identify five soil moisture conditions that occur during a year and present a conceptual model based on field studies and computer simulations of how streamflow is generated with respect to the soil moisture conditions. The five soil moisture conditions are 1) a summer dry period, 2) a transitional fall wetting period, 3) a winter wet, low flux period, 4) a spring wet, high flux period, 5) and a transitional late spring drying period. Transitions between the periods are driven by changes in the water balance between rain, snow, snowmelt and evapotranspiration. Low rates of water input to the soil during the winter allow dry soil regions to persist at the soil-bedrock interface which act as barriers to lateral flow. Once the dry soil flow barriers are wetted, whole-slope hydraulic connectivity is established, lateral flow can occur, and upland soils are in direct connection with the near stream soil moisture. This whole-slope connectivity can alter near-stream hydraulics and modify the delivery of water, and solutes to the stream.