Irrigation Water Allocation Calculator

This calculator determines how long it will take to use up an allocation of water.
Rationed allocation depth (D) : inches  
Area being irrigated (A) : acres  
Average rate of flow (Q) :  *   
  
* For surface irrigation operators, system capacities can be selected in cubic feet per second (cfs).

Example

For example (using conventional on-farm irrigation units), if a centre pivot sprinkler is irrigating 130 acres and has an average flow rate capacity of 900 U.S. gallons per minute (US gpm), a 300 mm (12-inch) allocation of water would be used up after 32.7 days.

This is calculated by the formula:

T = 18.857 x D x A / Q

where :
T = allocated time of delivery (days)
D = rationed allocation depth (inches)
A = area being irrigated through the diversion (acres)
Q = average rate of flow or system capacity (U.S. gpm)
18.857 = measurement units conversion factor

This information maintained by Lloyd Healy
Document Last Reviewed August 6, 2009