202 ENGINEERING FOR LAND DRAINAGES. 



the cost and care of such drains. Experience has 

 demonstrated that in well-watered sections tile drains 

 which are intended to provide outlets for large tracts 

 cannot be made large enough without too great ex- 

 pense to take care of exceptionally heavy rainfall with- 



FiG. 40.~-Tiie Dram with Relief Surface Ditch. 



out the aid of surface drains. Another reason for the 

 necessity of this provision is that many soils which 

 under ordinary conditions will respond readily to the 

 action of tile drains in removing water from the surface 

 through the soil will not permit a sufficiently large 

 quantity of water to pass to the drains in the short time 

 required. If the ditches are left broad and shallow they 

 will cause but little inconvenience and may be utilized 

 for cultivated field crops or for grass. 



An estimate of the cost of the entire proposed work, 

 including construction, legal and administration ex- 

 pense, should be made and apportioned to the several 

 property owners and interests concerned in the work. 



The Theory of Classification of Lands. 



The first step to be taken in determining the appor- 

 tionment of cost which each tract of land should bear 

 is to fix upon some scale of marking which shall 

 numerically express the benefits to each tract of land, 

 and which may be used in making a just and equitable 



