152 



MOSQUITO ERADICATION 



"In this case, no box is constructed, but heavily-timbered bulk-heads 

 are built into the stream until they stand within approximately 6 feet 

 of each other. To render their relation to each other constant, they are 

 bound together by heavy cross-timbers. At a point half-way between 

 the two ends, a pair of heavy, 6 by 6-inch well-braced timbers are set 



(Photos by California Corrugated Culvert Company) 

 Fig. 106. — Battery of Calco culverts and gates in process of installation. 



down in such a fashion as to form the support and resting-place for the 

 tide-gate. Of course, the joints between each of the upright posts and 

 ths bulk-head against which it stands and between the lower cross 

 timbers and the bottom are made tight. 



"The tide-gate is suspended from a cross-timber located well above 

 extreme high tide, and hangs against the upright posts. At each end, 



