Location: Great Basin Rangelands Research
Project Number: 5370-13610-001-17
Start Date: Sep 01, 2013
End Date: Sep 30, 2015
Rainfall simulation will be used to quantify the hydrologic, erosion, and salt mobilization and transport response on targeted ecological sites defined by the BLM in the upper Colorado River Basin. Four to six plots per ecological site will be used to quantify salt mobilization and loading as a function of existing soil and vegetation condition. Rangeland Health, National Resource Inventory and BLM Annual Inventory and Monitoring assessments will be collected at each experiment site to allow for correlation to measured infiltration, runoff, erosion and salt transport. To quantify the hydrologic response of the different ecological site, we will use a rainfall simulator (2 m wide x 6 m long) with rainfall rates at 5 and 50-year return period rainfall events (Appendix I). We will follow, in general, the rainfall simulation procedures that were developed during the USDA Water Erosion Prediction Project to quantify soil characteristics, infiltration, runoff, and erosion rates. Rainfall simulation plots will be characterized prior to rainfall simulation to document vegetation (canopy and ground cover, standing biomass, and plant height). Post rainfall simulation ground cover will be reassessed to quantify changes in distribution in ground cover as a function of runoff and soil loss. Soil surface attributes (topography, bulk density, aggregate stability, surface texture, and soil salinity) will be quantified before and after rainfall simulation. Depth of wetting front will be quantified after each rainfall simulation experiment to estimate transport of salts to vadose zone. Three digital cameras will be mounted on the rainfall simulator to provide for a synoptic view of the entire plot (1-mm pixel resolution) and will be used to identify the gap frequency between shrubs. A digital camera will be located on a trolley mounted on the outside frame of the simulator (2 meter AGL) and a picture will be taken along the entire perimeter of the plot with 90% overlap for the development of a plot digital elevation model. Images will be taken before and after rainfall simulation allowing for determination of soil movement (both loss and deposition) to be calculated. In addition, time-lapse photography from the overhead cameras during the rainfall simulation will allow us to trace fluorescent dye applied at the top of the plot as it is transported down slope. We will quantify the number and distribution of concentrated flow paths and how they change as a function of rainfall intensity using commercially available image analysis software, such as ERDAS and ESRI (ArcGIS 10). These data will also be used to develop model parameters for RHEM for predicting runoff, sediment yield, and salt loads. RHEM model performance will be evaluated using the Nash and Sutcliffe coefficient by using observed data versus modeled predicted runoff volume, peak flows and sediment yield.