Hydrological impacts of microwatersheds in the Des Moines Lobe

Potholes are features with no evident natural outlet, formed in hydric landscapes, such as the Prairie Pothole Region (PPR). Potholes are commonly under cropland management, which is not consistent with their hydrological patterns since periodic flooding during the growing season is frequent. Although there are studies investigating undisturbed and/or restored potholes, there is limited information about the hydrology of features that are farmed and artificially drained, a common situation in the Des Moines Lobe, the Iowan part of the PPR. The estimation of pothole hydroperiod and water balance variations would allow their hydrological classification and estimation of their potential environmental impacts. To estimate pothole hydrology, Annualized Agricultural Non-Point Source model (AnnAGNPS), was used in this project to model two potholes located in Story County, IA, for which we had two years of periodic measurements of inundation depth. For a better understanding of the features, a high-resolution DEM was used to study their potential volume storage, before overflowing. A conserved scenario, in which the potholes were consider to be retired from cropland production and from artificial tile drainage was also simulated to estimate potential hydrological impacts of pothole conservation. After model calibration, AnnAGNPS was used to estimate pothole water volume and depth variations in the features under both current and conserved conditions, for 23 years of historical weather data. It was proved that AnnAGNPS can provide reliable representations of the observed data, particularly for water depth variations. Results include pothole hydroperiod, consecutive days of inundation, average water depth during ponding events, and frequency of overflow. In the current condition, the potholes water regimen suggests that these potholes are classified as semipermanent. Most ponding occurred in early stages of the growing season, and mostly lasted from one to two days, barely overwhelming their storage capacity. Nevertheless, crop failure is common within their extent, which indicates that their management does not agree with their hydrological patterns. In the conserved condition, potholes flooded more often, held water for longer periods, and exceed their maximum storage capacity more frequently than in the current scenario. Further research includes the assessment of potholes under different management conditions, improvement of AnnAGNPS tools to address wetland features, and investigation of the reliability of the results of pothole conservation.