100 MOSQUITO ERADICATION 



should not be employed without discrimination. There is no use 

 in going to a large expense in draining a pond that can be con- 

 trolled for much less money by stocking it with fish. Nor will 

 it pay to try to drain a swamp that can be protected at much less 

 expense by means of levees or dikes and tide-gates. 



On the other hand, drainage has many advantages in addition 

 to its value as an anti-mosquito measure. Large areas of swamp 

 and marsh lands have been rendered cultivable by proper drain- 

 age. Furthermore, in many places in the United States today, 



Fit;. 04. — Typical anti-mosquito ditching location. 



the land is not producing what it should, because it is not drained. 

 For this reason, money spent on anti-mosquito drainage fre- 

 quently returns a double profit — it improves the health of the 

 occupants of the land and also increases the productivity of the 

 land. 



Again, it often happens that the cost of draining swamp land 

 is more than paid for by the natural resources thereby rendered 

 accessible. Frequently, the lumber alone thus made available 

 is worth more than what the drainage cost. 



PRELIMINARY WORK 



Whether the project be large or small, it generally will pay to 

 study pretty closely the topography of the area. If the project 

 be large and the area involved be low and flat, sufficient levels 

 should be run to enable a contour map to be prepared; the main 

 ditch systems should be laid off accurately on the map and then be 



