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Show Utah Geological and Mineralogical Survey, Water- Resources Bulletin 14, 1970 Other long- term complex chemical processes, such as interaction of dissolved ions with carbonate and silicate sediments, will affect the ionic ratios. These processes may be negligible over a few years, but they should be considered in long- term projections of changes in brine chemistry. MEASUREMENT OF DISCHARGE THROUGH CAUSEWAY AND ESTIMATES OF LOAD MOVEMENT DURING 1969 WATER YEAR In order to evaluate the effects of the causeway on the lake hydrology, it is necessary to know something about the total quantities of water and dissolved solids moving in each direction through the causeway. During the 1969 water year ( October 1968- September 1969), measurements were made of discharge through the culverts and estimates were made of discharge through the fill. These data together with the concentration were used to calculate the load movement for the year and to define relationships, if any, between discharge and lake stage and stage difference across the causeway. Discharge through the Culverts Discharge in the culverts was measured by standard U. S. Geological Survey stream- gaging techniques. Velocity profiles were measured at four points across the cross section of the culverts ( figure 9). From these profiles and the areas of the measuring sections, a total discharge in each direction through the culverts was computed. Because the water moves in both directions in the culverts, turbulence occurs at the interface. The water surface in the culverts is not static and may surge as much as 1 foot during a measurement. For these reasons, the accuracy of the measurements of discharge is considered only fair. A total of 17 measurements, covering one seasonal range of lake stage was made in the east culvert ( figure 1). Fourteen measurements were made in the west culvert, covering about three- fourths of the seasonal lake cycle ( table 1). At some time between July 15 and August 7, one or more railroad carloads of fill material were accidently dumped into the west culvert, and flow through that culvert was eventually reduced to seepage through the dumped material. The water- surface elevation on each side of the causeway at the culverts was measured with a stadia rod and engineer's transit at the time of each discharge measurement. However, because of wave action at the edge of the fill, the elevation measurements were found to give only a general indication of the average elevation difference across the causeway during the discharge measurements. Average elevations obtained from the two lake- level recorders at the east end of the causeway ( figure 1 and table 5) were considered to be more representative than the stadia- rod measurements. Density readings were also taken at various depths at the midpoint of the culverts. The measurements in the culverts showed that the discharge northward was almost always much greater than the discharge southward. With the exception of the measurement of March 4, 1969, the lowest ratio of northward to southward discharges in the east culvert was about 4: 1. During the peak of the inflow season in April, there was no southward discharge at all through the culverts. The measurement made on March 4 is not representative of average conditions, but it does show what can occur during storm periods. At the time this measurement was made, the lake was very turbulent from storm activity; and a very strong wind was blowing from the north, giving an added impetus to the southward discharge. Southward discharge was observed through the west culvert only during storm periods. The bottom of the culvert is approximately 4 feet higher than the bottom of the east culvert, and it is only slightly higher than the point at which the interface usually was found in the east culvert. Unless the interface between northward and southward flow varies by a much greater amount than it did during 1969 ( about 2 feet), southward discharge through the west culvert will probably occur only during storm periods. Discharge through the culverts accounted for about 45 percent of the total brine moving northward through the entire causeway but only for about 15 percent of the total brine moving southward. An analysis of the data collected during the 1969 water year shows a fair relationship between discharge through the culverts and difference in lake stage across the causeway ( figure 10). The discharge northward increased with increasing difference in lake stage, whereas the discharge southward showed very little change with changes in stage difference. For the one seasonal lake cycle for which data are available, the stage difference across the causeway appears generally to be related to the stage of the south part of the lake ( figure 11). The difference in lake stage tends to increase with increasing lake stage. However, the relationship shown in figure 11 is too general to be used to predict the discharge through the causeway on the basis of lake stage. 19 |