Surface-subsurface modeling of water dynamics in drained and farmed wetlands in the prairie pothole region

Abstract

A hydrologic model was developed to investigate the surface ponding dynamics in a pothole complex in Iowa's prairie pothole region. This study includes a description of the ponding process, the identification of the main drivers of surface ponding, and an analysis of ponding depth and duration. The modeling was based on Saint-Venant and Richard’s equations to calculate overland and groundwater flows, respectively, using a coupled surface-subsurface approach. The model simulated eleven years (2011–2021) and was calibrated and validated using three datasets: water table measurements, surface ponding estimated from satellite images, and satellite-based estimates of evapotranspiration. Based on the simulations, the ponding process starts with direct precipitation and overland flow moving toward the pothole. Once water reaches the pothole, it infiltrates and percolates causing the water table to rise until it eventually reaches the ground surface. Surface ponding begins when the soil beneath the pothole is fully saturated and continues until the excess water is removed through evapotranspiration and the tile drainage network. Results indicate that surface ponding is primarily driven by overland flow, with 64.1 % from direct precipitation and 35.9 % from runoff, while groundwater rise has a negligible contribution. The model results indicate an average infiltration rate of 25 mm/day and average ponding depth and duration of 6.8 cm and 3.6 days, respectively. Analysis of the simulated ponding duration reveals a reduction in crop yield in 2 of the 11 years, with total crop loss occurring in 6 of those years.