Effect of geomorphologic resolution on modeling of runoff hydrograph and sedimentograph over small watersheds

In hydrologic models, Geographic Information Systems (GIS) interfaces are commonly used for extracting the channel network, and delineating the watershed. By overlaying soil and land use maps onto the extracted channel network, input files required by the model are prepared. However, the nature of the extracted channel network strongly depends on some pre-selected threshold values within the GIS framework, which in turn, determine the geomorphologic resolution. There are no accepted guidelines for selecting these threshold parameters making the extraction of channel networks a subjective process. In this study, we investigate the effect of geomorphologic resolution on runoff hydrographs and sedimentographs over two small USDA experimental watersheds. The KINEROS model with ArcView interface has been used for this purpose. An empirical relationship between optimal resolution, watershed characteristics and nature of the storm has been developed. Results reveal that geometric simplification of the watershed for rainfall-runoff-erosion studies may be acceptable under right combinations of rainfall events and watershed properties. Our results also indicate that the optimal geomorphologic resolution may not be the same for hydrographs and sedimentographs.