DRAINAGE OF IKEIGATED SHALE LAND. 



37 



For the first year the discharge 

 from this drainage system averaged 

 43 gallons per minute, or about 

 0.095 of a cubic foot per second, 

 practically the entire quantity of 

 which was collected by the 35 relief 

 wells in about 1,000 feet of tile. 

 The hydrograph shown in figure 11 

 was plotted from measurements at 

 the outlet of the system made at 

 irregular intervals during the first 

 14 months after the drains were in- 

 stalled. It indicates the discharge 

 in gallons per minute and shows 

 a marked seasonal fluctuation. As 

 determined from this hydrograph, 

 the flow from the relief wells has 

 averaged 1.2 gallons per minute 

 per well. The quality of the drain- 

 age water is indicated by analyses 

 F and G in Table I. 



Considering the size of the af- 

 fected area, the quantity of water 

 developed is unusually large for 

 this type of land, and would indi- 

 cate the source of supply to be 

 either leakage from the canal one- 

 half mile north or the seepage of 

 water supplied on not less than 20 

 or 30 acres of the higher-lying 

 lands in the neighborhood. In 

 either case, before reaching the 

 drains the water must pass through 

 shale for several hundred feet. 

 While the upper 3^ feet of soil on 

 this tract has been dried out thor- 

 oughly, the efficiency of the drain- 

 age system would have been in- 

 creased by installing the main 

 drain up the backbone of the shale 

 ridge 8 feet deep instead of 6 ; more- 

 over, another lateral drain with 

 relief wells is needed, beginning 

 400 feet north of the outlet of the 

 system, where the main tile line 







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