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t ~ [ ~ ~ I ~ ~ 1 ~ I I r I I I . I t r I N o 0') 0' CHAPTER IV FIELD INVESTIGATION RESULTS FROM THE STUDY Salinity and the Price River Basin The time pattern in which the salt load is carried by the Price River results from a complex combination of interactions among time variable hydrologic processes. Natural groundwaters seep slowly into the stream to evaporate in the dry bed leaving encrusted salt behind. Waters diverted for irrigation leach salts from soil, and the return flows also add salt as the seep into the stream. Storm runoff hydrographs rise rapidly, picking up salts dissolved on the bed, churning bed sediments, and carrying the salts mixed with those sediments. After the storm, the flows recede rapidly," and the salts and sediments return to the bed a distance downstream from where they were before, determined by the size of the storm. Return flows work to keep the stream flowing through the dry season, carrying a more concentrated salt load, initially because of the salts leached from the soil and over the long run because of the consumptive use of wa ter. For general representation of the time patterns, daily flows and conductivities (a surrogate for total dissolved solids) are plotted for 1970 in Figure 4.1. As flow is an important factor determining salt trans- port, daily conductivities are plotted versus average daily flows for the Price River at woodside for the 5-year period 1970-74 on a log-log basis (Figure 4.2). The line follow- ing the form of Equation 1.3 and having the best fit is shown on the figure and has a correlation coefficient of 0.648. The student t-test (Lapin 1975) showed the null hypothes is that the slope of the regression line was equal to zero to be rejected at the 99 percent confidence level. The conclusion at this point was that flow is definitely significant in determining salinity but that other factors also need to be considered. According to Hendrickson and Krieger (1964), one needs to explore the different mineral dissolution characteristics of water flowing into the stream along various paths. Gunnerson (1967) explained the hysteresis in the annual pattern of monthly flows and conductivities for Columbia River subbasins in terms of the annual variation in dominant flow paths. Discharge and salinity profiles along the Price River are shown by Figures 4.3 and 4.4, respect ively, for data taken dur ing a sampling survey on October 19 to 21, 1976 (Appendix B, Table B.3). Most of .the flow was being diverted from the river above the City of Price (river mile 10). Downstream from the city, both the flow and the salinity increased rapidly. The predominant cations were sodium, calcium, and magnesium, and sulfate was the main anion. Figures 4.3 and 4.4 together suggest that the Price River salinity loading largely enters the stream by return flows and tributary inflows below Price. To aid in identifying diffuse salt. source areas in the Price River Basin, Mundorff's (1972) water quality samples of varying repetition at 71 sites over a 3D-year period (Figure 4.5) were evaluated statisti- cally. The sample sites were considered independent treatments, and mean salt load- ings per sample site were calculated as pounds per day per square mile of drainage. The null hypothesis that the treatment means were equivalent was tested by comparing an individual treatment with the average of the rema ining treatments. Student t-values were calculated (Neter and Wasserman 1974), but the results were not conclusive. Three sampling sites, numbers 31, 50, and 52 (Figure 4.5), were identified as collecting runoff from areas of high salt loading. The three (Drunkards Wash, Desert Lake Wash, and Desert Seep Wash) drain irri- gated farm land and exhibit a high average salt load, 518, 416, and 423 pounds per square mile of drainage per day, respective- ly. Drunkards Wash exhibited a large salt load in part because one of the sampling observations was made during a storm surge transporting a large flux of salt. Figure 4.6 shows the major tributaries and canals in the proximity of Desert Seep Wash and Desert Lake Wash with average observed conductivity levels at measured points. As indicated by this figure, the average salinity level of the Price River increased by approximately 30 percent at its confluence with Desert Seep Wash. However, because of the strong influence of -agricul- ture, Desert Seep Wash was not examined further in this study of salinity contri- butions from natural areas. 23