title: Examination of a Non-point Source Loading Function For the Mancos Shale Wildlands of the Price River Basin, Utah
Creators: name: Ponce, Stanley L.
Publisher: name: Utah State University
Year: 1975

description: During 1974 and 1975 a diffuse source salinity study was conducted in east-central Utah. The specific objectives of this study were (a) to determine the role of overland flow on salt movement for selected land types, (b) to determine the relative magnitude of surface erosion associated with overland flow and its role in the salt release process, and (c) develop a non-point source loading function to predict salt production from diffuse sources.
The Rocky Mountain Infiltrometer technique was utilized to study the process of overland flow and its relation to salt transport. A reconnaissance survey was made during the 1974 summer field season. Surface runoff water chemistry results indicated (a) the Undivided Mancos and Lower and Middle divisions of the Blue Gate members are major contributors of salt to surface runoff, (b) salt concentrations are highest as surface runoff begins, (c) salt concentrations of the runoff water are fairly low relative to t he water in the Price River and (d) natural field variability is related directly to the salinity of the surface runoff.
Soil analysis showed the 1:1 soil:water extract of the surface crust had a high linear correlation with the salinity of the surface runoff. The results of the soil studies suggested a very thin zone of interaction between soil and overland flow in terms of salt production.
Suspended sediment concentrations tended to vary directly with the salinity concentration of the surface runoff.
During the 1975 field season studies were made to examine the processes and mechanisms of salt release to overland flow and collect data for the development of a non-point source loading function. Plot length studies showed that beyond 5 feet (1.5 meters) plot length has little effect on the salinity of surface runoff. Rainfall intensity is related to runoff salinity through two basic processes. First, when a change in rainfall intensity is not accompanied by a direct change in erosion rate, the salinity of the runoff varies inversely with rainfall intensity, suggesting dilution phenomena dominate. Second, when rainfall intensity is increased and accompanied by erosion, salinity of runoff varies directly with intensity, suggesting salinity is directly related to the mineral salts associated with the sediment.
Linear correlations between suspended sediment and runoff salinity failed to reject the hypothesis that the salinity of the runoff is not related to the suspended sediment concentration.
At relatively constant rainfall intensities, the salinity of the runoff followed the trend of a decay function and became constant after l8 minutes. When rainfall intensity was varied, the salinity of the runoff responded unpredictably to the intensity rather than the duration.
Micro-watershed studies revealed (a) the development of a salt crust at the surface by evaporation of soil moisture has little effect on the salinity of the surface runoff, (b) runoff follows the same general trend as the rainfall with time after the initial abstractions have been met, and (c) there is only a slight relation between the runoff salinity and the rainfall intensity and runoff rate. A high degree of variation was found to exist in the salinity of the surface crust over a small area.
A large degree of natural variation associated with the data complicated the development of non-point source loading function. Several functions, derived from both physical and empirical concepts, were examined. The function which provided the best results was a simple multiple regression equation of the form TDSc=B0+B1P+B2Q. An example of how this function could be used to solve a typical problem was developed and worked out.
The magnitude of the salt mass added to the Price River annually by surface runoff occurring over Mancos shale lands was calculated from results of this research and found to be 0.5 percent of the total annual salt mass transported by the river.