Evaluation of various types of mechanical control devices 5/ 



In the following paragraphs the various types of devices for the 

 control of sea lampreys mentioned frequently in this and earlier re- 

 ports are evaluated as an aid in the planning of sea lamprey control 

 programs o x 'ive types of devices have been refined to a point where 

 they may be considered effective, if somewhat expensive, control 

 mechanisms o 



(l) Permanent- type weirs and traps similar to that installed in 

 the Ocqueoc River for capturing spawning runs (Figure 12) « 



Although the Ocqueoc River weir and traps, as installed, 

 were functionally satisfactory, their structural characteristics 

 were not„ Designs have been tentatively worked out for a permanent- 

 type sea lamprey weir which will be a vast improvement over the 

 Ocqueoc weir in stability and ease of operation . Construction 

 materials are reinforced concrete and steel throughout,, This type 

 of structure can be placed in streams of moderately large size and 

 of almost any width orovided it can be so installed th^t not more 

 than 5 feet of water will pass across the deck of the weir during 

 flood stages. This limitation on depth is necessary because of 

 the very narrow spacing required in the grates (racks) or screens 

 of a sea lamprey weir; any aperature or spacing wider than l/2-inch 

 will permit the upstream escapement of smaller individuals. It is 

 almost impossible during floods to keep the grates of such a weir 

 cleared of water-borne trash by manual means where the water depth 

 is greater than 5 feet„ Presently designed structures will handle 

 up to 2,500 cubic feet per secondj larger volumes can undoubtedly 

 be handled with proper designing. 



Permanent-type structures of suitable design can be installed 

 at an average unit cost of $222.00 per linear foot of structure, 

 exclusive of engineering and construction-supervision costs. This 

 figure is based on engineering estimates prepared for a typical 

 group of larger northern Michigan streams. It is not recommended 

 that these structures be built at right angles to the direction of 

 stream flow (shortest distance across stream). No economy can be 

 attained in a long-term program of operation by such construction. 

 The impounding action of the structure creates serious erosion 



5/ These devices are distinguished from electrical (electronic)^ 

 chemical^, and biological control devices or- techniques which are 

 currently under investigation. 



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