Development of a SWAT Hydrologic Model to Predict Salt Transport in an Upland Desert Catchment of the Lower Arkansas River Basin in Colorado

Excess salt loading from watersheds acts as a chemical stressor in water bodies which can lead to significant impacts on water quality and crop growth. High salinity threatens sustainable crop production on a global scale and is especially prevalent in semi-arid and arid regions. For this reason, salt transport in irrigated semi-arid and arid regions has been intensively studied. However, little research has been conducted to evaluate the salinity contributions of dominantly non-irrigated, high-desert basins in similar climatic regions. The objective of this research is to utilize the Soil and Water Assessment Tool (SWAT) to evaluate the contribution of salt to the Arkansas River from the Purgatoire River, a dominantly non-irrigated desert catchment in southeastern Colorado. The newly developed SWAT-Salt, which includes the fate and transport of major salt ions in soils, aquifers, and streams, is used to accomplish this task. The ~3450 mi2 Purgatoire River basin is susceptible to high salt transport due to very high topographic slopes (with a mean slope of 41%), sparse vegetation, presence of salt minerals, and intense summer thunderstorms that drive sediment load into streams. An accurate hydrologic model of the Purgatoire River basin is crucial to evaluating salt transport in various components of the water balance, including in-stream cycling, surface runoff, soil percolation, lateral flow, and groundwater exchange. The SWAT-Salt model is tested against streamflow and in-stream salt ions loads at multiple gaging sites within the Purgatoire River basin. The development of this model will enable evaluation of the effects of climate and land management practices on the spatio-temporal patterns of salinity transport and loading in high-desert watersheds. One predicted outcome of this research is a forecast model for total annual salt load given total annual precipitation/evaporation in a region. This research will also indicate whether natural, largely undeveloped basins export relevant salt loads as compared to heavily irrigated regions.