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. .... " ~ ):s t ., temperature profiles measured at transects 3 and 5 in September 1985 (fig. 8). During December, the reservoir surface was frozen from the inflow to tran- sect 3. The temperature profile measured at transect 3 during December indicates that the reservoir was inversely stratified at this site (fig. 8). At transect 5, the temperature decreased 1.5 DC throughout the water column; at transect 7, the temperature profile indicates that the water column was completely mixed. Outflow from the dam may have hydrodynamically induced mixing at transect 7 in September and December. Temperature layering in Pueblo Reservoir is controlled largely by air-temperature variations, water temperature of the Arkansas River entering the reservoir, the volume of inflow and outflow in relation to volume of water in the reservoir, reservoir mor- phology, and the position of the reservoir in relation to wind patterns. In addition to evaluating stratification, water-temperature measurements were used to evaluate initial routing of the Arkansas River within the reser- voir as either overflow, interflow, or underflow. Overflow occurs when in- flowing water flows across the reservoir surface and doesn't mix with colder, more dense water because the inflow water density is less than the reservoir water density. Interflow occurs when the inflow enters at an intermediate depth, because the density of inflow is greater than the epi1imnion but less than the metalimnion or hypolimnion. Underflow occurs when relatively colder water enters the reservoir and flows to the lowest depth of the reservoir because the inflow water density is greater than the reservoir water density (Wetzel, 1983). As the Arkansas River enters Pueblo Reservoir, the incoming water flows into a layer in the reservoir that has an equivalent density. However, as water moves through the reservoir, the water's temperature and density change as the result of solar heating, evaporative cooling from wind, and conduction. Therefore, the inflow routing shown in figure 9 should be interpreted only as routing of inflow within the upstream part of the reservoir, and the arrows showing the initial routing of inflow in figure 9 cannot be extended confi- dently along the same isotherms throughout the entire reservoir. During the 1985 season, underflow occurred in Pueblo Reservoir because the temperature of the Arkansas River was less than, and the density was greater than, that of the reservoir water. Because Pueblo Reservoir was stratified and because stratification controls mixing and circulation patterns within the reservoir, underflow water or hypolimnetic water could be expected to remain in the lower strata beneath the thermocline as the water moved through the reservoir. Specific Conductance Differences in specific conductance measured throughout the water column can indicate water layers that have differing dissolved-solids concentrations. With respect to specific conductance, the water in Pueblo Reservoir was strat- ified during 1985 (fig. 10). During June 1985, specific conductance measured at transects 3 and 5 indicates that a marked decrease in dissolved-solids concentration occurred below the thermocline (figs. 8 and 10), probably as a result of underflow from the Arkansas River that carries snowmelt water with small concentrations of dissolved solids. The specific-conductance profile measured at transect 7 in June (fig. 10) indicates the presence of several water layers of differing dissolved-solids concentrations. During September 24