DETERMINING WATERSHED FLOW PATHWAYS USING GEOCHEMISTRY AND TIMING

Investigating storm runoff generation in watersheds is an area of ongoing hydrologic research. Geochemical tracer studies, such as static end-member mixing analysis (EMMA) and hysteresis loop analysis, have been used to evaluate these processes. While EMMA can assess the relative input of flow pathways during a storm, it cannot quantify their contributions. Hysteresis loops of stream discharge versus geochemical tracer concentration can be used to estimate relative inputs of basic end-member pathways, but this approach only suggests the timing and dominance of flow pathways and cannot quantify their contributions.

We propose a new method that incorporates both hysteresis loops and geochemical tracer studies to quantify runoff contributions from watershed flow pathways during a storm. The approach involves estimating relative tracer concentrations of four end-members, along with estimating the percentage and timing of total stream discharge supplied by each component. Analysis of storms at Panola Mountain Research Watershed, Georgia has revealed at least two storm runoff generation patterns occurring at the site: one that is dominated by pre-event water and another where event water is a major contributor to storm runoff.