Submitted to: Water Resources Bulletin
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/1994
Publication Date: N/A
Citation: Interpretive Summary: In many mid-central states of America, agricultural drainage wells (ADWs) are traditionally used to drain excess water from surface and/or shallow groundwater to deeper aquifers to sustain crop productivity in agricultural lands with poor natural drainage. Recent concerns of groundwater contamination due to agricultural chemicals brought up the debate between general public (concerned about water quality) and farmers (agricultural land owners) to evaluate and devise any alternative route for the chemical-laden excess water from an agricultural watershed in Iowa. In this study we simulated the water-logging condition in the watershed and the effect of excessive-water-stress on crop production following the closure of ADWs. A distributed modeling approach in conjunction with a geographical information system and crop stress models were used over a twenty year period. The results indicated that closure of ADWS in the watershed could result ponding in low-lying areas and poorly drained soils, making them unsuitable for crop production. Moreover, there is a 60 percent chance that crop yield loss in the watershed could exceed 18 percent for any year out of the twenty years considered in the study. Furthermore, our GIS-based modeling approach could give high resolution distributed maps for input parameters and simulation results, thus, helping the decision makers to focus on the problem areas.
Technical Abstract: Much of north-central Iowa is characterized by flat topography, shallow depressions, and poor natural surface drainage. Land drainage wells (ADWs) are used as outlets for subsurface drainage of cropland under corn and soybean production. Studies have shown that these drainage systems, mainly the ADWs, are potential routes for agricultural chemicals to underground aquifers. To protect the region's vital groundwater resource, researchers are evaluating alternative outlets ranging from complete closure of existing ADWs (and creation of wetlands) to continued use of ADWs and chemical management in a comprehensive policy framework. This study couples a geographic information systems database for a 471-hectare watershed in Humboldt County, Iowa, with a groundwater flow model (MODFLOW) and an empirical crop yield loss model to predict long-term effects of complete closure of ADWs on crop production. The cropland areas inundated and the relative crop yield loss due to ADW closure are determined as a function of long-term climatic data. The results indicate that elimination of drainage outlets in the watershed could result in ponding of low-lying areas and poorly drained soils, making them unsuitable for crop production. Such wetness also decreases the efficiency of production in the no ponding areas by isolating fields, and the crop yield loss can be reduced by an annual average of abut 18 percent.