Rapid water-level fluctuations in a thin colluvium landslide west of Cincinnati, Ohio

A modified Dupuit hillside flow model shows that water levels will fluctuate uniformly along the entire slope in response to either an increase or a decrease in net recharge (due to either rainfall or evapotranspiration) and that wavelike downhill flow can occur only when net recharge is negligible. For each storm observed, total rainfall was divided by total change in groundwater level to derive an estimate of pre-storm maximum effective porosity. These figures ranged from 1 to 7% for all but one of the storms. It was found that effective porosity values in the range of 1 to 3% gave a much better simulation of actual water-level records when used in a finite-difference approximation of modified Dupuit flow, suggesting that the hillside must have been at or very near tension saturation before the storms of record. The model is very sensitive to a combination of effective porosity, hydraulic conductivity, rainfall intensity, and rainfall duration. -from Authors