3-COMPONENT TRACER MODEL FOR STORMFLOW ON A SMALL APPALACHIAN FORESTED CATCHMENT

A three-component 18O tracer model recognizing contributions of groundwater, soil water and channel precipitation was used to represent stormflow in Rish Run, a small Appalachian Plateau forest stream. The traditional two-component model recognizing 'old' and 'new' water stormflow sources fail to explain runoff events in Fish Run, often giving 'old' water percentages of stormflow exceeding 100%. With the three-component model, channel precipitation contributions were computed from measured throughfall intensity and channel area. Example computations for a low-intensity frontal rainfall event using the three-component model gave stormflow contributions of 0.9% for channel precipitation, 24.1% for soil water and 75% for groundwater. Contributions of soil water to stormflows may explain levels of dissolved aluminum toxic to fish found in several Appalachian Plateau streams.