Subsurface Drainage Peak Flows in Shallow Soil

Abstract

The subsurface drainage operation of shallow soils is characterized by sudden and brief peak flows followed by long‐lasting tail recessions. A field experiment was conducted on a seasonally waterlogged, shallow loamy soil in Arrou, France, under temperate climate. Rainfall and drainage discharge were recorded on an hourly basis, as well as water tension profiles and water‐table levels at different distances from the trench. Observed peak flows are related to sudden increases in the horizontal hydraulic gradients near the trench and to the stability of the water‐table shape. Using these results and extending Boussinesq's usual transient‐state approach, SIDRA, a theoretical model in which soil vertical heterogeneity is taken into account, has been elaborated and applied to simulate by finite differences hourly water‐table levels and drain flow rates. The paper compares observed and measured values of the winters of both 1980–81 and 1985–86.