Pore Water Uptake by Agricultural Runoff

Abstract

The entrainment of soil pore water by overland flow is examined. In a series of laboratory experiments water was passed at various velocities and depths over a soil bed. The soil was saturated with sodium bromide solution prior to each experiment. Runoff water was sampled at the end of the flume and analyzed for bromide concentration. From these data, mass loss rate and cumulative mass loss curves are developed. A Fickian diffusion model is formulated to describe mass transfer from the soil interstices to the overland flow. A procedure to determine the coefficient of diffusion from experimental data is developed and implemented. In general, laboratory results exhibit typical Fickian behavior for large time. The diffusion coefficient varies with velocity, depth of flow, soil surface roughness, and soil condition. Early runoff data, however, exhibit distinct non‐Fickian behavior.