what diminutive weir and trap can be built and installed in a 1G- 

 foot-wide stream Tor less than -$50.00. If a greater volume of water 

 must be handled than is indicated above or if the volume of flow is 

 estimated at greater than IiO cubic feet per second, it is recommended 

 that the stream bed and banks be so altered as to permit the installation 

 of a Carp Greek style structure. 



These nortable weirs, if properly installed, are amazingly sturdy 

 and will give many years of service. The prototype of this weir in 

 Carp Creek, Presque Isle Co., Michigan, has been used for four consecutive 

 year 1 : and will serve for many more before the replacement of any of its 

 parts is necessary, However, the limitations of the device should not 

 be overlooked and where any doubt exists as to its ability to handle 

 spring floods, only a permanent-type weir should be considered. 



(h) Dam and inclined-screen trap units of the Carp Lake River type 

 for capturing young downstream migrants (Figs. 13 and 16) . 



This device is extremely effective in capturing all of the 

 youngs recently transformed sea lampreys which are moving down- 

 stream to begin their parasitic existence in the lakes. It can be 

 installed, however, only in streams in which it is practical to 

 construct a dam. The flat topography of the land and the generally 

 low gradients of the streams of the Lake States thus place a limit- 

 ation on the use of this device. At least a 5-foot head must be 

 created by the dam in order that the tailwater will not interfere 

 with the installation or operation of the trapping screens. It is 

 frequently difficult, at least in Michigan drainages, to find a 

 satisfactory site in the lower water-course where a dam creating 

 such a head can be built, 



Generally speaking, the use of the dam and inclined-screen 

 trap is probably limited to those streams that are less than 75 feet 

 vd.de and in which only mild, or at. worst moderate, spring floods occur. 



The pilot model of this type of structure was installed and 

 developed in the Carp Lake River, Emmet Co,, Michigan, by the Michigan 

 Department of Conservation at an aggregate cost of approximately 

 £6,000.00, Although the Carp Lake River was originally only 33 feet 

 wide (at mean level) at the ooint of construction, a 90-foot, double- 

 i.'all dam was required because of the porosity of the surrounding soils. 

 Installation cost will, therefore, vary widely with stream and soil 

 ditions and resulting construction requirements. 



(h) Barrier dams for diverting spawning runs of sea lampreys such 

 as that installed in the Black River, Mackinaw Co., Michigan (Fig. 17). 



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