Irrigation Diversion Study 



During this biennium the irrigation diversion study discussed in 

 the Biennial Report of the Fish and Game Commission for 1950-52 

 was completed. Two reports ' '' were published and a pamphlet^ was 

 printed by the Fish and Game Commission giving a brief discussion of 

 fish losses in irrigation diversions and giving practical methods of 

 reducing these losses. The Commission extends its grateful apprecia- 

 tion to the Montana State Agricultural College Experiment Station 

 for its major role in this cooperative project. 



The solution to fish losses in irrigation diversions has invariably 

 hinged on fish screens or salvage operations. Many experimental in- 

 stallations have been tested by the Fisheries Division and in 1942 it 

 was concluded that annual maintenance alone for a statewide screen- 

 ing program would cost three times as much money as was available 

 for the operation of the entire Division. 



In addition it has been demonstrated conclusively in the present 

 study, at least for canals in the Gallatin Valley, that fish losses to 

 any one canal are small enough so that conventional type fish screens 

 cannot be installed and maintained economically. 



Fish salvage is equally impractical because the high cost of 

 crews and equipment does not permit the wide application necessary 

 to effect an appreciable reduction of the over-all loss. 



This study demonstrated that proper headgate manipulation can 

 be expected to save as much as 35 percent or more of the pounds 

 of trout lost to individual ditches. Reductions in water flow exposes 

 fish and stimulates movement. Most of the fish so stimulated travel 

 in an up-canal direction until they reach the river or find cover in 

 the form of pools, undercut banks, or heavy overhanging brush. Fish 

 travel greater distances whenever a uniformly smooth canal bottom 

 and a minimum of cover exists. These observations have lead to the 

 recommendation of two management measures: 



1. It is recommended that all ditch companies reduce the flow 

 in ditches abruptly three days prior to headgate closure in 

 the fall, or at any other time during the year when headgates 

 are closed. Shorter reduction periods are beneficial and can 

 be applied anytime conditions favor decreased flow tluring 

 iirigation season. The amount of decreased flow will depend 

 primarily on the opening under the headgates. This opening 

 should be not less than three inches high. If this spacing 

 does not reduce the flow to the lowest level capable of sup- 



'Clothier, William D. 1953. Fish loss and movement in irrigation diversions from 

 the West Gallatin River, Montana. Journal of Wildlife Management, Vol. 17, No. 2: 

 pages 144-158, April, 1953. 



-Clothier, William D. 1954. Eiiecl of water reduction on lish movement in 

 irrigation diversions. Journal of Wildlife Management, Vol. 18, No. 2; pages 150- 

 160, April, 1954. 



'Clothier, William D. 1953. Methods of reducing tish losses in irrigation diversions. 

 Montana Fish and Game Department pamphlet, 5 pages. 



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