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<br />OG~137 <br /> <br />15 <br /> <br />Incremental (IFG4) Method <br /> <br />The Incremental Method using the stage discharge approach was <br />completed with the cooperation of and input from personnel of the <br />Instream Flow Service Group. Avera~e depth and avera~e velocitx <br />were the only two parameters used in formulatin~ minimum flow <br />recommendations with the Incremental Method. <br /> <br />The average depth, average velocity, and recommended instream <br />flows for each transect are given in Table 6. All three parameters <br />for each transect were totalled and averaged. The average recom- <br />mended flow in cfs was the discharge level used to compare with <br />results of the other methodologies. As was the case with the mul- <br />tiple transect R-2 Cross, the parameter that first became limiting <br />or co-limiting was average depth, 60 times out of 96, or 63% of the <br />time. <br /> <br />\ <br />1 <br />I <br />I <br />1 <br />l <br />I <br />I <br />i <br /> <br />In determining the flow level at which either average velocity <br />or average depth became limiting, generally the flow was taken either <br />just above or just below the point at which that factor became limit- <br />ing. Possibly all values should have been interpolated to get the <br />exact flow level at which one parameter became limiting. However, <br />I felt this was unnecessary in most instances since the requested <br />discharge levels (Q) were usually only a few cfs apart. In instances <br />where the differences between adjacent discharge levels was 10 cfs <br />or greater then exact values were interpolated. Where adjacent input <br />Q requests were only 1 to 5 cfs apart, I felt the differences would <br />average out, i.e., one flow was actually too high, the other too low, <br />producing very nearly the same average flow as if all recommended <br />flow levels had been interpolated exactly. <br /> <br />Ihe Incremental Method produced minimum flow recommendations <br />that closely approximated those from the Single and Multiple Tran~ect <br />.R-2 Cross Method. Since average depth was the determining factor <br />in the vast majority of instances for both methods it is perhaps <br />not so strange that minimum flow recommendation from the two methods <br />would agree quite well. <br /> <br />The Incremental Method offers great advantages over the R-2 Cross <br />Methods because of its capability of interfacing with the IFG3 or <br />Habitat Computer Model. This system allows for a detailed analysis <br />of the stream habitat available to the trout at any flow regime de- <br />sired. This facet of the study will be discussed in subsequent sections. <br />