Comparison of the Iowa State University Effluent Limitation Guidelines Model with the Soil-Plant-Air-Water Model for Evaluating Containment Basin Performance

This article compares results from the Iowa State University Effluent Limitations Guidelines (ISU-ELG) model to results obtained using the Soil-Plant-Air-Water (SPAW) model to simulate feedlot runoff containment basin overflow volume. The objective was to verify that the ISU-ELG model was providing a reasonable prediction of basin overflow. The ISU-ELG model uses a set of guidelines to determine if land application is acceptable, whereas the SPAW model uses a soil moisture criterion. The criterion for determining if a particular day was suitable for land application of basin effluent was investigated to determine the effect on basin overflow volumes. The results show that the ISU-ELG model overpredicted the percentage of feedlot runoff controlled in comparison to the SPAW model at all five locations investigated. For wetter areas in Iowa, the number of drying days had a large effect on basin overflow volumes, whereas for the drier northwest region of Iowa, this effect was limited. Possible methods of improving the ISU-ELG model predictions include adding a soil moisture accounting function to model moisture levels in the land application area or calibrating the number of drying days required before land application can commence. Alternatively, the SPAW model can be used, but this requires additional user inputs and increases complexity in modeling the runoff control system.