DRAINAGE 65 



determine if possible the fertility of the land after improving. 

 Then the drainage engineer should go over the tract in order 

 that he become thoroughly familiar with it before under- 

 taking any instrument work at all. If the tract is large and 

 if the ownership is divided, care should be taken that all 

 work from the outset shall conform to the law of the state in 

 which the tract is located. 



The Extent of the Survey. In the drainage of all but the 

 smallest areas it is quite necessary to make the preliminary 

 survey before attempting in any way to decide upon the final 

 plan. The purpose of the preliminary survey is to obtain the 

 data from which the final plans must be made. The data 

 secured should include the area of the drainage basin, 

 location of the water-shed, direction of the slopes and water 

 courses, and should indicate soil conditions and possible 

 outlets. 



In securing this data it is necessary that the work be done 

 carefully. Mistakes are costly and can only be avoided by 

 careful work in securing correct information in the prelim- 

 inary survey. Careful work with crude instruments is often 

 more satisfactory than hasty work with expensive equip- 

 ment. 



Investigation of the Subsoil. An investigation of the 

 character of the soil and subsoil should be made a part of the 

 preliminary survey, for on the data thus secured will depend, 

 to a large extent, the depth of and distance between tile 

 lines. This is quite important in land that is underlaid 

 with sand and gravel or with an impervious stratum of clay. 

 These investigations can best be made with the soil auger. 

 This tool can be made by welding a long handle to an ordinary 

 \ l /2 or 2-inch carpenter's auger. See Fig. 53. 



Preliminary Instrument Work. An engineer's level 

 should be used in the preliminary survey to obtain elevations 



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