CONSTRUCTION NOTES 239 



(a) For direct removal of surface water which may accumulate as the 

 result of storms, or of water which may be confined in pools of various types. 

 Thus in the case of surface water to prevent erosion by admitting it to an 

 underground channel. 



(b) For removal of ground water in order to accomplish the following 

 results: (i) To eliminate the danger of damage from expansion during 

 freezing weather in the vicinity of foundation walls, graves, walks and roads. 

 (2) To aid the normal growth of vegetation by preventing the drowning of 

 roots in supersaturated soil, and by reduction of moisture content to encour- 

 age bacterial activity for root growth. (3) To eliminate undue softness of 

 areas, caused by surplus ground water where a firm surface is desired. 



Fundamental principles of drainage. There are certain fundamental 

 principles which apply to the practical analysis and eventual solution of a 

 drainage problem. The general method of approaching a drainage problem 

 may be summarized in the following tabulation: 



(a) Determine the exact nature of the problem that is, whether the 

 problem is one of surface water removal entirely, one of subsurface or 

 ground water removal where it is desired to effect a permanent lowering of 

 the water table, or whether the problem is a combination of these factors. 

 In so doing a decision will be reached regarding the portion of surface water 

 to be removed by surface channels and the portion of surface water together 

 with ground water to be removed by underground pipes. 



(b) Determine the time element in the removal of surplus surface 

 water or ground water that is, whether temporary backing up is per- 

 missible and if so at what points in the system. 



(c) Determine the quantity of run-off from the area to be drained and 

 the resulting size of open ditch or sizes of pipe required under the time 

 element. 



(d) Determine upon the solution of the out-fall portion of the problem, 

 so that the total construction cost will be most economical. 



(e) Determine upon the type of channel, pipes and inlets in different 

 parts of the area to be drained which will accomplish the most economical 

 and effective solution under the conditions imposed. 



(/) Determine upon a proper spacing of the individual drainage lines 

 so that the entire system will be adequate to remove surface or ground water 

 as required, and allow a factor of safety which will meet with demands of 

 abnormal and unexpected quantities of water. 



(g) Determine the proper depth for various drainage lines in order to 

 answer the requirements of their individual functions. 



(k) Determine the available minimum grades which can be accepted, 

 and plan if possible the entire system as a unit, making ample provision 

 for future extensions without readjusting the entire plan. 



