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Gain-Loss/Conductivity Surveys. Two gain-loss/conductivity studies were performed on Dry <br /> Creek 7/19/93 and 11/9/93. Figure 7-7 shows the five locations along Dry Creek at which <br /> the flow and water quality measurements were taken. The summer gain-loss study (July 1993) <br /> showed flow losses between Stations 1 and 2, 3 and 9, and 4 and 5 with the greatest flow <br /> loss (19 gpm) occurring between Stations 4 and 5. The channel flow stayed constant between <br /> Stations 2 and 3. During the fall survey (October 1993), flows were lower overall, bu[ two <br /> of the reaches showed increasing flow rates in the downstream direction. Between Stations <br /> 1 and 2 there was a 6.7 gpm increase in flow and between Stations 3 and 9 there was a 1.7 <br /> gpm flow increase. The fall evidence of gaining reaches due to ground water inflow is most <br /> probably due to the fact ET rates were at a minimum and the effects on bank storage Ithere <br /> had been several storms prior to the fall survey) were also negligible. Conductivity <br /> values ranged from 9,510 to 9,770 }unhos/cm in the summer survey to 3,630 to 5,970 pmhos/cm <br /> in the fall survey. Conductivity levels consistently increased in the downstream direction <br /> during both surveys, excepting between Stations 9 and 5 in the summer survey where there <br /> was a 190 }imhos/cm drop. The greatest increase in flow between stations showed a <br /> contluctivity increase of 40 pmhos /cm, while the greatest decrease in flow showed a <br /> contluctivity increase of 1,500 pmhos/cm. Conductivity values were higher in the summer <br /> (except between Stations 9 and 5), while flows were also higher and ground water <br /> contributions were not measurable. Reaches showing ground water inflow do not appear to <br /> cause any greater increases in conductivity than losing reaches. Conductivity increases <br /> appear to be slightly correlated to flow rates and reductions in flows. The greatest <br /> increase in. conductivity occurred in the reach with the greatest drop in flow rate and the <br /> lowest downstream flow. The gain-loss and conductivity survey data are summarized in Table <br /> 7-8. During the surveys, there was no water being diverted from Dry Creek for irrigation <br /> purposes and there was no irrigation tailwater flowing into Dry Creek. Also, there was no <br /> flow from Stokes Gulch during either survey. Thus, the results of the surveys are <br /> reflective of natural conditions unaffected by irrigation withdrawals or discharges. <br />Seasonal Variability and Trends. Tables 7-5, 7-6, and 7-7 present the stream water <br />chemistry data for monitoring sites HGSD1, HGSD2, and HGSD3 (through May 1997: more recent <br />data is preaented in the Annual Hydrology Reports, which are submitted to CDMG under <br />separate cover). The analytical results presented in Table 7-5 and Table 7-6 indicate some <br />seasonal variability in Concentration for several constituents at both the up-stream <br />(HGSD1) and downstream (HGSD2) sites. The major ions, bicarbonate (HCO3) sulfate (SOy), <br />calcium (Ca), magnesium (Mg) and Sotlium (Na), all increase slightly during the baseflow- <br />dominated months (August-November) in comparison with the spring snowmelt period, although <br />no discernible change in water type occurs. TDS also increases in concentration at both <br />sites after snowmelt ends and lower <br />TR-07 19 Revised 03/06 <br />