Process-based modeling of upland erosion and salt load in the Upper Colorado River Basin

Authors: Nouwakpo, Sayjro; Weltz, Mark; GREEN, COLLEEN - BUREAU OF LAND MANAGEMENT; MCGWIRE, KENNETH - DESERT RESEARCH INSTITUTE

Submitted to: Federal Interagency Hydrologic Modeling Conference
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: The Colorado River is a vital municipal, agricultural and ecological resource in the United States and Mexico but is susceptible to detrimental salinity levels. The U.S. Bureau of Reclamation estimates that damages due to salinity of the Colorado River are estimated at $385 million per year. Over 55% of sediment and salts entering the Colorado River is of natural origin with a significant contribution from accelerated soil erosion on federal rangelands. Knowledge on salt pickup and transport processes is limited to a few studies linking salt transport to soil erosion. As a consequence of this knowledge gap, no tool exists to satisfactorily predict salt load to surface waters in the Upper Colorado River Basin (UCRB). In this study, we aim to develop parameter estimation equations that are valid on saline rangeland sites for use in the Rangeland Hydrology and Erosion Model (RHEM). Data from rainfall simulation experiments at 9 sites in the UCRB were used to develop these predictive equations. At each experimental site, rainfalls of intensities corresponding to the 2-, 10-, 25- and 50-year return frequency for the area were simulated at a rate of 1 event per plot, resulting in a total of twelve plots per site. Plot dimensions were 6 m x 2 m. During each rainfall event, traditional soil erosion measurement data (runoff rate and volume, soil loss and sediment concentration) were collected along with information on soil salinity and sodicity represented by Electrical Conductivity EC and Sodium Adsorption Ratio (SAR). The newly developed equations for the effective hydraulic conductivity and the splash and sheet erodibility adequately captured infiltration, runoff and erosion processes on saline rangelands. The performance of the RHEM model at predicting runoff and soil loss was improved with the usage of the new equations compared to the original equations. Overall, the effective hydraulic conductivity was greater on these saline rangelands compared to that predicted by the nonsaline RHEM equation. Erosion was overall greater on these rangelands and was a positive function of the Sodium Adsorption Ratio. A linear function between soil loss and total dissolved solids in runoff was used to predict salt load from soil loss data. These new equations will be integrated in a new version of the RHEM model to provide a tool for land and water resource managers to evaluate erosion, runoff and water quality on salt-affected rangelands.

Technical Abstract: The Colorado River is a vital municipal, agricultural and ecological resource in the United States and Mexico but is susceptible to detrimental salinity levels. The U.S. Bureau of Reclamation estimates that damages due to salinity of the Colorado River are estimated at $385 million per year. Over 55% of sediment and salts entering the Colorado River is of natural origin with a significant contribution from accelerated soil erosion on federal rangelands. Knowledge on salt pickup and transport processes is limited to a few studies linking salt transport to soil erosion. As a consequence of this knowledge gap, no tool exists to satisfactorily predict salt load to surface waters in the Upper Colorado River Basin (UCRB). In this study, we aim to develop parameter estimation equations that are valid on saline rangeland sites for use in the Rangeland Hydrology and Erosion Model (RHEM). Data from rainfall simulation experiments at 9 sites in the UCRB were used to develop these predictive equations. At each experimental site, rainfalls of intensities corresponding to the 2-, 10-, 25- and 50-year return frequency for the area were simulated at a rate of 1 event per plot, resulting in a total of twelve plots per site. Plot dimensions were 6 m x 2 m. During each rainfall event, traditional soil erosion measurement data (runoff rate and volume, soil loss and sediment concentration) were collected along with information on soil salinity and sodicity represented by Electrical Conductivity EC and Sodium Adsorption Ratio (SAR). The newly developed equations for the effective hydraulic conductivity and the splash and sheet erodibility adequately captured infiltration, runoff and erosion processes on saline rangelands. The performance of the RHEM model at predicting runoff and soil loss was improved with the usage of the new equations compared to the original equations. Overall, the effective hydraulic conductivity was greater on these saline rangelands compared to that predicted by the nonsaline RHEM equation. Erosion was overall greater on these rangelands and was a positive function of the Sodium Adsorption Ratio. A linear function between soil loss and total dissolved solids in runoff was used to predict salt load from soil loss data. These new equations will be integrated in a new version of the RHEM model to provide a tool for land and water resource managers to evaluate erosion, runoff and water quality on salt-affected rangelands.