Submitted to: American Society of Agricultural Engineers
Publication Type: Proceedings
Publication Acceptance Date: 11/15/2000
Publication Date: N/A
Technical Abstract: Runoff volumes from plots can be quite variable. These variations can be important for understanding the hydrologic system, and also to evaluating the effectiveness of infiltration and runoff prediction models. We investigated the sources of variability among 40 replications in a previously reported experiment on fallow plots. A numerical model was calibrated using data from the experiment and from other published data. Approximately 70% of the observed variation among the replicated plots could be explained by the spatial variabilities of hydraulic conductivity, surface storage, and the depth to claypan. Changes in the relative differences in runoff among plots may be explainable by the modification of the spatial distribution of hydraulic conductivity and surface storage during tillage. The introduction of these sources of variability in the model formulation produced a realistic description of the variance of the observed values of runoff, as well as a relatively clear delineation between the explained and unexplained variability. These results can serve as an index of model performance in predicting observed data.