HR: 16:00h
AN: H42K-01 INVITED     [PDF]
TI: Moving beyond the variable source area concept for defining the hydrologic and geomorphic process controls on water quality
AU: * McDonnell, J J
EM: jeff.mcdonnell@orst.edu
AF: Dept. of Forest Engineering, Oregon State University, Corvallis, OR 97330 United States
AB: A variety of hydrologic and geomorphic processes influence surface water quality via event-based flushing of labile nutrient stores and between-event weathering reactions along subsurface flowpaths. A central paradigm in our modeling of these processes rests with the Variable Source Area concept, articulated by John Hewlett almost 50 years ago. Rapid progress is being made on the water quality modeling front modeling vis-…-vis parameter estimation techniques, model uncertainty analysis, examination of parameter identifiability in our models, downward approaches to hydrologic prediction, etc,. However, I wonder if we have neglected somewhat, updating our understanding of the rainfall-runoff process and the basic questions of: Where does water go when it rains? What flow path does it take to the stream? How long does it reside in the catchment? These questions, while basic, lie at the heart of understanding the coupled hydrologic and geomorphic processes influencing water quality. This talk will explore how our sharpening perception of water source, flowpath and age in upland headwater catchments is increasingly at odds with variable source area theory. The variable source area concept has been distilled into our widely used research model structures by collapsing the process complexity into simple mathematical assumptions of things like the decline in saturated hydraulic conductivity with depth, steady-state catchment water table response, topographically defined water flowpaths and linear wetting and drying from the valley bottom upwards to the ridge (depending upon storm size, intensity and antecedent wetness conditions). This talk takes a critical look at our process underpinning by discussing new field evidence of where water goes when it rains that directly challenges the status quo. New model structures informed by this new process understanding are then discussed in the context of how data and objective hydrologic and geomorphic discretization of catchment units may be used both to structure and test the model.
DE: 1866 Soil moisture
DE: 1899 General or miscellaneous
SC: Hydrology [H]
MN: 2003 Fall Meeting