WSP04021 - Laserfiche WebLink

Home Browse Search

40 where these cutthroat trout occurred had slow water velocities and silted beds. Despite problems with insufficient data for various life stage probability curves, the interfacing of the IFG3 Program with both the IFG2 (Water Surface Profile - WSP) and the IFG4 (Incremental) Methods gives it great potential for use in the natural stream environment. Methodologies in Relation to BioloRical Conditions The single and multiple Transect R-2 Cross methods are only indirectly related to the biological conditions of the stream through the parameters avera~e depth. averag~~el~ci~~an9_percent wetted perimeter. While some work has been done to summarize the average depth and velocity preferences for fish and aquatic invertebrates (Stalnaker and Arnette, 1976; Hooper, 1973; Water Resources Research Institute, 1978), in most instances the tol- erance ranges are so wide that any attempt to correlate fish numbers and/or biomass with the R-2 Cross output would be futile. Cover factors at present cannot be incorporated into this method. In short, the R-2 Cross probably has the least applicability of any tested method of stream flow assessment if correlation with the biological conditions in the stream is a necessity. The IFG4 model by itself probably has no more potential than the R-2 Cross model in relation to biological conditions. But the capability of interfacing with the IFG3 for a WUA output versus flow makes the IFG4 a powerful tool in assessing the re- lationship between discharge and the habitat conditions of the stream. With the IFG3 model now modified to accept input for stream cover, this program should become even more effective in assessing the relationship between weighted usable area and the actual bio- logical conditions occurring in the stream. This model may have its greatest application in predicting changes in species com- position resulting from drastic changes in flow patterns. It may also have application in predicting changes in WUA and trout standing crop that result from stream improvement projects. Scrutiny of the curves of WUA plotted against the annual discharge patterns for median water years, one in five high water year, and one in five low water years, reveals a very consistent pattern (see Appendix C). That pattern is that WUA invariably decreases during the periods of peak runoff in May, June, and July or conversely, the WUA increases during lower flow periods. Carrying this thought to its logical conclusion, the question arises, "ls too much water just as -.-ie_trimen_tal_ to ~ _st:ea~~rout population as too little?" I feel the answer is most certainly affirmative. Evidence indicates that .the stability of stream flow and the aquatic environment beneath it can actually be en- hanced by topping off some of the peak run-off. Surveys of streams in the headwater areas of the Colorado River basin in 1964