Closed‐form solution for finger width in sandy soils at different water contents

Abstract

Wetting front instability and gravity‐driven fingers can occur during infiltration in sandy soil. These soils overlay many major aquifers. Finger width and velocity are important parameters in predicting the risk of groundwater pollution in these soils. In previous studies, closed‐form solutions were developed for air dry soil. In uniformly wet soils, where the fingers are much wider, predictive finger width equations have failed so far. In this paper we simplify further the Parlange‐Hill closed‐form solution for dry soil and show that, by taking hysteresis into account, it applies to fingers emanating from a point source in a sandy test soil at two widely different moisture contents.