2001-12-11_PERMIT FILE - C1981010A (4)

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L;.i r.-1^lwiduV ooavaaarrou • f '_ • ) J It should be noted that the one mile between 2A and 2B had some possibly significant hydrologic features. A large por- tion had sandy bed and banks as contrasted with the cobble and occasional shale through most of the study reach. In this sandy area, the river broke up into a wide, partially braided (multiple) channel. The porous bed and banks combined with the much larger area in which the river contacts the bottom provide a greater opportunity for ground water exchange with the river, Also, several pockets of cottonwood trees and thick riparian vegeta- tion were observed betcaeen these stations. This may indicate the presence of springs or seeps. These factors lend support to the possibility of ground-water discharge between 2A and 2B. While it also appears from Figure 4-1 that significant gains may have occurred after Station 4, errors associated with measurements at Stations 6 and 7 on 30 and 31 August made those values less reliable. The excellent-rated measurements of 29 August indicated no change in flow over this stretch. For the most part, conditions were considered ideal. The river was at base flow, no diversions or tributaries were active other than Williams Fork, flow was steady and clear at j all measuring stations, and the weather was good. Due to the ideal conditions and the consistency of the field data, the hydrologists felt that the data gathered could be given a high a level of confidence. Of the 21 measurements made, 15 were rated excellent, or within two percent of the actual flow. Excluding the loss area, all of these measurements were within two percent _ of one another on each day. ~ •~ As a further check, the flow at the last station above the confluence with Williams Fork was subtracted from the Station 6 flow (below the confluence). This difference was then compared to the measured flo~o in Williams Fork (Station 7). As can be seen 4-4