278 THE MOSQUITOES OF NEW JERSEY 



pleted can shrink the $20,000 figure to $4,000, thus immediately be- 

 coming very practicable. Furthermore, it is believed that the same ma- 

 chine will be able to cut new ditches at as low a cost as any other 

 machine thus far developed. 



Ditches on the salt marsh forty inches or wider will have to be recut 

 by hand or by small caterpillar dredges, unless new continuously-oper- 

 ating machinery is later developed. Fortunately, the amount of this 

 type of recutting is but a very small percentage of the total. 



TREATMENT OF THE ENCLOSED SALT MARSH 



In some instances the drainage established by nature has been so 

 interfered with by the activity of man in the building of railroads, road- 

 ways, dikes and banks, that reopening sufficiently wide outlets has be- 

 come impracticable. Furthermore, this shutting in has in some cases 

 so interfered with the vegetation that it has died and the marsh surface 

 lowered in extreme cases as much as 3.5 feet. To make a bad matter 

 worse, at many points the raw sewage from large populations has been 

 emptied into these artificially formed basins. 



The solution of the problem is to shut out the sea and remove such 

 water as occurs behind the barrier either by gravity through sluices or 

 with pumps. A considerable fund of experience is now available for the 

 treatment of shut-in marshes that have and have not shrunken. About 

 6,000 acres have been thus completely treated for mosquito control. 



The problem of the enclosed, nonshrunken and sewage free marsh is 

 relatively simple because gravity furnishes all the power necessary to 

 move the water. 



Of course, the first step is the installation of internal ditching 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 (Spartina patens) and 

 the presence of rows of debris brought in by the extra high tides, there 

 is good reason to believe that in most seasons a dike would prove a use- 

 less expense. In such cases it is merely necessary to install sluices and 

 tide gates in the principal outlets and to block up the others, connect- 

 ing them with the principal ones. 



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

 dicated by the presence of coarse grasses (mainly Spartina alterni- 

 flora) and the absence of lines of debris, or when the agency concerned 

 wishes to provide against extreme tides, the portion of the area ad- 



