SEASONAL PREFERENTIAL FLOW IN 2 SIERRA-NEVADA SOILS UNDER FORESTED AND MEADOW COVER

The preferential movement of surface-applied solutes is a potential source of groundwater contamination and could subsequently provide a major source of nutrients to Lake Tahoe. This study investigated seasonal infiltration, water repellency, and preferential water flow in two Sierra Nevada soil types (a granitic and a volcanic soil) in forest and meadow areas using a rainfall simulator. Infiltration and runoff were measured at the plot surface. Plots were subsequently excavated to measure preferential water flow. Water repellency was found to affect infiltration and nonuniform preferential Bow was observed. The volcanic soil demonstrated continuous preferential flow with depth, whereas in the granitic soil, preferential Bow rapidly dissipated. Wetting patterns showed greater preferential low in the forested areas for both soils compared with the meadow areas. Higher initial water content and reduced water repellency in the early spring generally produced more typical matrix water flow in the coarser textured granitic soil. Since preferencial flow was most evident in all forested conditions, nutrient bypass potential is considered greatest on soils in forested areas near tributaries and the lake.