"ji N. J. Agricultural Experiment Station, Bulletin 348' 



age-free marsh) is relatively simple because gravity furnishes all' 

 the power necessary to move the water. 



Of course the first step in the drainage of the enclosed area is- 

 the installation of internal drainage of the type used on the open- 

 marshes. Whether dikes are necessary in such an area depends on? 

 the height of the meadows adjacent to the tide. When the natural 

 land is well above mean high tide, which is usually indicated by the 

 presence of prolific growth of salt grass (and the presence of a row 

 or rows of debris brought in by the high tides) there is good reason 

 to believe that in most seasons a dike would .prove a useless expense. 

 In such cases it is merely necessary to install sluices and tide-gates in 

 the principal outlets and to block up the others, connecting them witb 

 the principal ones. Credit for the discovery and first utilization of 

 this plan for mosquito control must be given to John Dobbins, of 

 Newark. 



When the land bordering the tidal water is low, which is usually 

 indicated by the presence of coarse grasses and the absence of lines or 

 rows of debris, or when the agency concerned wishes to provide against 

 extreme tides, that portion of the area adjacent to tidal waters must 

 be protected by a low dike and the water inside outletted by sluices 

 and tide-gates. 



The questions of dike, sluice and tide-gate construction for agri- 

 cultural purposes have received a considerable amount of attention 

 and the facts have been pretty well covered in Bulletin 240, of the- 

 Office of Experiment Stations, U. S. Department of Agriculture, 

 Washington, D. C, and reports of the State Geologist of New 

 Jersey. The utilization of this construction for mosquito control is 

 comparatively recent but already it has been modified better to serve 

 the purpose. 



The height of the dike is made to depend upon the height of the- 

 tide it is expected to keep out. In one case the dike was built to an 

 elevation of 7 feet above mean low tide, which was 3^ 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 dikes as they were built stood 3 feet above the meadow sur- 

 face, were 2 feet wide at the top and 6 feet wide at the bottom. 

 Antici]jating a shrinkage of about 25 ])er cent, the crest was made 

 about I foot higher than the elevation called for. 



