The Dawn of a New Constructive Era 79 



so wet that the growing or cultivating of crops becomes impos- 

 sible. 



The drainage of these low-lying level lands can usually be 

 accomplished readily by the construction of properly designed 

 drainage improvements. To design adequate drainage improve- 

 ments the needs of each district must be considered separately. 

 The first step is to make a survey of the lands involved. This 

 survey should include a determination of the location, size and 

 fall of the existing drainage channels, the relation of these chan- 

 nels to the area needing drainage, and the amount of land that 

 will be drained by each watercourse. Sufficient elevations should 

 be secured so that a clear idea of the character of the topography 

 can be obtained. During the progress of the survey notes should 

 be made of the vegetation, the character of the soil, and the 

 apparent need of the various tracts for drainage. After the sur- 

 vey is completed a careful study should be made of the data 

 secured, of the existing rainfall records, and of records of the 

 amount of run-off from the areas in question or similar areas 

 nearby in order to determine the amount of water that must be 

 removed from the area which it is proposed to drain. Upon the iow-luino""" 

 proper determination of the amount of water that must be re- Level Lands 

 moved depends to a large extent the successful operation of the 

 drainage improvement. Many factors affect the amount of water 

 that will be discharged from a given watershed. The principal 

 factors are: Rainfall, topography, size and shape of the water- 

 shed, evaporation, climate and seasons, soil, geological structure, 

 proportion of forest and open land, character of vegetation, nat- 

 ural reservoirs and artificial improvements affecting drainage. 



After the amount of water that must be removed has been 

 decided upon the proper size of the ditches can be readily com- 

 puted by commonly known engineering formulae. In general the 

 ditches should have ample depth. For dredge ditches eight feet 

 is probably a minimumi depth under ordinary conditions. The 

 excavated material should not be placed closer than eight feet 

 to the edge of the ditch and if the ditch is very deep the distance 

 should be much greater. 



The drainage ditches should be so located that they can be 

 readily reached by the landowners whose lands they are supposed 

 to benefit. The topography of the district and the character of 

 the farm drains that will be used are usually the deciding factors 

 in determining the location of the ditches. 



