Long-term, process-based, continuous simulations for a cluster of six smaller, nested rangeland watersheds near Tombstone, AZ (USA): Establishing a baseline for event-based runoff and sediment yields

摘要

Accurately predicting long-term, process-based runoff and sediment yields measured at the outlet of even small watersheds can be challenging. The assessments following careful parameter determination enable establishing a baseline for local land management to assess policy implementations and rehabilitation especially under climate or land use/cover changes. Process-based, continuous models have demonstrated their advantage of representing event-based hydrological responses at smaller spatial and temporal scales. In this study, the Geospatial interface for the Water Erosion Prediction Project (WEPP) is validated for a series six, neighboring, nested subwatersheds (101 to 106) at Lucky Hills, Walnut Gulch Experimental Watershed (WGEW), Tombstone, Arizona (USA). The primary objective of this study is to assess short-term parameterization and long-term verification and simulation validation of GeoWEPP based on 55 years of runoff and sediment yields for six subwatersheds. The effective hydraulic conductivity (K_(eff)) parameter is adjusted based on runoff observed in watershed 101 using a research-grade 1 m-Digital Elevation Model (DEM). The performance of runoff simulated generated by an aggregated 5 m-resolution DEM lead to better results in contrast to using the original 1 m- or aggregated 3 m-resolution. Since there are no sediment yield observations for that watershed, the similar sized, neighboring watershed 102 and a publicly available DEM were used to parameterize critical shear. The short-term verification of K_(eff) as well as the long-term verification of K_(eff) and critical shear stress indicate that both parameters generated based on one subwatershed can be used to accurately predict the runoff in all other watersheds in the study area. However, the results have a tendency to slightly over-estimate runoff, and become more significant with the distance from the rainfall and runoff gauges for the watershed that was used for the K_(eff) parameter estimation. For sediment yields, the results indicate that the short-term parameterization of shear stress based on one watershed can potentially lead to significantly different results for neighboring watersheds. The results are the baseline for spatially distributed shear stress and channel erosion parameter validation and impact assessment for future climate and land use changes.