50 ENGINEERING FOR LAND DRAINAGE. 



a greater length of drain will be required to accomplish 

 the same purpose. 



Bring all land whicli is deficient in natural drain- 

 age under tlie influence of tile drains. This requires 

 the investigation of the entire watershed for the pur- 

 pose of determining how complete the natural drainage 

 is. The engineer should adopt in his own mind some 

 standard of the degree of thoroughness with which he 

 proposes to drain a given tract, and locate his drains 

 with reference to the natural wetness of the land. He 

 should find out whether the water comes from the sur- 

 face of some adjoining higher land, or from distant 

 springs, or is seep-water from slopes. If parts of the 

 field are naturally dry, or as dry as it is proposed to 

 make the other parts, he should pass it by and put 

 drains in the wetter portions so as to bring them up to 

 the standard. It may be remarked that portions of 

 land which are supposed to have sufficient natural drain- 

 age have afterward been found deficient in this respect, 

 when compared with the land that is thoroughly tiled. 



Data Required for Locating Drains, 



The knowledge of a piece of land which is necessary 

 for the proper laying out of a drainage system may be 

 obtained in one of two ways or partly by both. 



Firsts the engineer may, by carefully inspecting the 

 land with the aid of some one who is familiar with both 

 surface and soil peculiarities, determine upon the proper 

 system and mark out the lines readily. There is a 

 feature connected with the location that is gratifying to 

 the engineer, which is that, when the correct and nat- 



