OBJECTIVES 



■- A.- .■ ■ 



The Montana Department of Fish, Wildlife and Parks began 

 in 1966 to estimate standing crops (numbers and biomass) of 

 trout in the rivers of the Missouri drainage of southwest Mon- 

 tana. Presently, long-term standing crop estimates are avail- 

 able for five reaches of the Madison, Beaverhead, Gallatin 

 and Big Hole rivers, all nationally acclaimed wild trout 

 fisheries. In these five reaches, the flows, which are gaged 

 by the USGS, are either regulated by dams or affected by ir- 

 rigation withdrawals. Annual variations of the standing 

 crops of trout within each reach were found to be related to 

 annual flow variations. From these relationships, instream ; .* 

 flow recommendations were derived for the five reaches . 



The use of long-term standing crop and flow data is not -' 

 a practical means of deriving future instream flow recommen- 

 dations due to the excessive time, cost and manpower require- 

 ments involved in collecting data. Because of these limita- ■■: 

 tions, flow recommendations for other waterways in Montana 

 will primarily be derived from instream flow methods that 

 incorporate little if any biological data. The reliability 

 of the recommendations generated by the methods in current 

 use has not been adequately documented. Acceptance of these 

 recommendations has generally been based on theoretical con- ■ 

 siderations and professional judgment rather than biological 

 proofs. The instream. flow recommendations derived from the 

 standing crop and flow data for the five river reaches pro- 

 vide a biologically derived standard for comparing the recom- 

 mendations generated by the instream flow methods. 



In this study, four instream flow methods were applied 

 to each of the five river reaches and their flow recommenda- 

 tions compared to those derived from the long-term standing 

 crop and flow data. The four methods chosen for evaluation 

 were (1) a single transect method utilizing the IFG-4 hy- 

 draulic simulation model, (2) a multiple transect method 

 utilizing the Water Surface Profile (WSP) or "Pseudo" hy- • 

 draulic simulation model, (3) a non-field method utilizing 

 historical discharge records, and (4) the incremental method 

 developed by the Cooperative Instream Flow Service Group (IFG) 

 of the U.S. Fish and Wildlife Service. In addition to evalu- 

 ating the reliability of the recommendations generated by 

 each method, other objectives were to compare the final flow ' 

 recommendations to the monthly hydrograph for each reach, 

 determine the cost, time and manpower requirements associ- 

 ated with each method, and assess the predictive capabilities " 

 of the IFG-4 and WSP hydraulic simulation models. 



