46 Quantity of Water Consumed in Irrigation. 



APPENDIX B. 



Calculation of the Average Loss of Water by Perco- 

 lation from the Ganges Canal during the Cold Season 

 of 1875-76. 



Let D = mean discharge flowing during the season (152 days) = 

 4447 c. ft. per second. This may have been gauged in the main 

 canal, thus including loss in the canal itself (case A), or more probably 

 (case B), the gauging may have taken place at the distributary heads, 

 thus excluding loss in the canal (see par. 7). 



A = area irrigated during the season = 571,907 acres. 



a = ,, ,, per c. ft. per sec. of discharge = A -5- D = 



128 "6 acres. 



Q = average quantity of water consumed daily on the whole 

 canal = 4447 X 86,400 = 384 million c. ft. 



q = quantity consumed per acre = 152 Q -4- A = 102,000 c. ft. 



q G = quantity used in the fields per acre (51,000 c. ft. — see par 13) 

 = q -f- 2. 



q a = quantity per acre lost before reaching the fields (51,000 c. ft. 

 — see par. 15) = q -—■ 2. 



Qa = quantity lost daily on the canal, bearing the same propor- 

 tion to Q that q a does to q .'. Q a = Q -r- 2 = 192 million c. ft. 



Qc = quantity used daily in the fields = Q — Qa = 192 million c . ft. 



I = average length in miles of channels (large and small) traversed 

 by the water from the point where it is gauged to the fields, after 

 allowing for closures (tdtHs) during the season. 



7r = wetted perimeter of various channels in feet. 



M = miles of wetted surface of channels one foot in width = I X ""• 



w = wetted surface in sq. feet = 5280 M. 



d = depth in feet lost by percolation daily. 



Then— 





Total lengths 

 in operation. 



I 



IT 



M = Z 



X 7T. 





Case A. 



Case B. 



Canal 



Distributaries 

 Village watercourses . 



miles. 

 579 

 3386 

 (See 



miles. 



400 



2500 



below.) 



feet. 



100 



12 



40,000 

 30,000 

 30,000 



30,000 

 30,000 



Totals .. 



100,000 



60,000 



The length of village watercourses has been assumed at 3 or 4 miles 

 per mile of distributary, and ic = 3 or 4 feet ; then, area is about the 

 same as that of distributaries. Field-channels (see 3c?, par. 4) are 

 not included. 



