PRINCIPLES OF MOSQUITO CONTROL 279 



jacent to tidal waters must be protected by a low dike and the water 

 inside let out by sluices and tide gates.* 



A,.,tf'„uiifc to,..oiii,..W.., ^ 



Fig. lxxxv. Diagram of sluice box and tide gate. 



The height of the dike depends upon the height of the tide. In one 

 case the dike was built to an elevation of seven feet above mean low tide, 

 which was one half foot higher than the previously recorded highest 

 tide for the season of 1914. The intention was to build it high enough 

 to keep out all but the very highest of high tides, the theory being that 

 these extraordinary high tides come so rarely and at such times of the 

 year that fencing them out is unnecessary. 



The early dikes as they were built stood three feet above the meadow 

 surface, were two feet wide at the top and six feet wide at the bottom. 

 Anticipating a shrinkage of about twenty-five per cent, the crest was 

 made about one foot higher than the elevation called for. When the 

 construction of the dike began, a trench ten inches wide by twenty 

 inches deep was cut along the line to be occupied by the structure, and 

 the sods taken out were utilized as part of the dike. A row of sods com- 

 posed of pieces approximately ten inches wide, twelve inches thick, and 

 twenty-six inches long was laid on each side of this trench with the 



* The questions of dike, sluice, and tide-gate construction for agricultural pur- 

 poses have received a considerable amount of attention, and the facts have been 

 pretty well covered in Bulletin 240 of the OflBce of Experiment Stations, U. S. De- 

 partment of Agriculture, Washington, D. C, and reports of the State Geologist of 

 New Jersey. The utilization of this construction for mosquito control is compara- 

 tively recent, but already it has been modified to serve the purpose better. 



