surface and soon becomes stagnant. Heavy mosquito breeding 

 follows. The problem, therefore, is to devise a drainage system that 

 will provide adequate outlets for the highland storm water and will be 

 so arranged that tide-water will circulate and change with the ebb and 

 flow of the tide and not remain pocketed on the marsh surface. This, 

 of course, is a problem in engineering, the solution of which is too 

 detailed to be more than outlined in a booklet of this nature. 



Where the meadow 

 under consideration 

 is an open one, fairly 

 high and not too re- 

 mote from its ulti- 

 mate outlet, a series 

 of ditches 10 inches 

 wide and 30 inches 

 deep is dug to pro- 

 vide channels, and 

 shallower spur ditch- 

 es are cut to reach 

 isolated pools and 

 holes. These ditches 

 are not designed to 

 run entirely dry ; the 



Fig. 15— (above). The 

 Result of Drainage 

 Shallow salt-marsh 

 pool dried out by drain- 

 age, killing the mosqui- 

 to wrigglers. 



Fig. 16— (to the right). 



KlLLlFlSH — THE GREAT 



Natural Enemy ot 

 the Salt-Marsh Mos- 

 quito. 



1— Male: 2— Female. 



water changes with each tide and the killifish ( a natural enemy ot 

 mosquito larvae), enter upon the scene and devour such wrigglers a.* 

 occur in the ditches themselves. In some places, certain] natural for- 

 mations make the standard 10-inch ditch impractical and a 20-inch. 

 W)-inch, or even wider ditch is used. 



Sometimes a salt marsh has been practically cut off by a railroad 

 or highway and has settled to such an extent" that gravity drainage 

 is not feasible, or sometimes the marsh is so low that good drainage 

 cannot be obtained by means of ditches only. In such cases, the 

 area is completely shut off with dikes fitted with tide-gates. The 

 dike is practically a sea wall or small levee. The gates work auto- 

 matically. When the tide comes up, the gates close and when the 

 ride goes out, the gates open and release the water accumulated during 



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