Relation of Depressional Flooding to Soil Water and Upstream Accumulated Flow

Abstract

<abstract> Depressions may pond with water even when tiles, inlets, and ditches are present. Untiled wetlands lose more water to infiltration and evaporation since water is not lost through tiles. Water use by wetland vegetation around the wetland creates a gradient that induces lateral flow of the infiltrated water; however, field crops are often killed by flooding in the depression. The purpose of this study was to (1) use a water balance approach for calculating distribution of water to and from the depression, including modification for risers attached to inlets, and (2) relate ponding to upslope soil water deficit and crop growth around the depressions. Two depressions were monitored with “surface” wells. The north depression was larger and had two slotted risers for the two inlets, so the calculation procedure had to be modified to allow for risers. The south depression had only one inlet with no riser. For each rain event, the maximum inflow was calculated for the upslope flow accumulation. Smaller rain events saw lateral additions of only a fraction of maximum inflow because water infiltrated before reaching the depression. Calculated lateral inflow and tile outflow were too high for some events due to plugged and backed-up tiles under high flow rates. Soybean (Glycine max (L.) Merr) was killed by the extended ponding in 2010, and corn (Zea mays L.) growth was stunted in 2011, reducing evapotranspiration around the depressions. Overall, the water balance approach was useful to understand water storage and loss from depressions within a field in relation to soil water before the rain.