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wondering what is tO' be gained by transferring the water from 

 the many little pools on the meadow surface to the ditches. Why 

 would not water in ditches make as good a home for mosquito 

 larvae as the water in the shallow depressions of the meadow's 

 surface ? 



There are two conditions which make the ditches safe. The 

 first of these is on the undiked meadow where the rising and 

 falling tide sweeps back and forth through the ditches and washes 

 the larvae out to sea. The second is where the water in the 

 ditches is kept in such a condition that killifishes thrive and 

 eat the mosquito larvae. There is a danger on the diked meadows 

 that the water in the ditches may become so stagnant or polluted 

 that the killifishes will die, leaving an excellent home for mosquito 

 larvae. 



This diagram shows the theoretical arrangement of a meadow 

 ditched and diked and provided with tide-gates. The horizontal 

 lines represent the lo-inch ditches connected with larger ditches, 

 all behind the dike, but connected with the tidewater outside 

 through the tide-gates at the lower corners of the diagram! (fig. 

 7)- 



When carefully designed and operated this system of drainage 

 will keep the water in the ditches nearly one foot below mean 

 tide, or sea level, except during and just after heavy rainfalls. 

 Should the water in these ditches become too stagnant or polluted, 

 it is proposed to freshen it and restore, the killifishes by causing 

 a circulation of water through the ditches. This is to be accom- 

 plished by fastening some of the tide-gates in an open position, 

 permitting the high tide to enter and distribute itself through 

 the system of ditches and pass out through other tide-gates 

 which are kept working normally. Thus, if the lower right- 

 hand gate were fastened open the high tide would flow in at that 

 point, and by putting stops to some of the ditches the water 

 could be made to circulate at will through any part of the 

 system. This is the theory, but you will see by the maps 

 which will be shown that there are practical difficulties which 

 make the solution of the problem not as easy as might at first 

 appear. 



