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Determining Agricultural Water Loss In The Great Lakes Basin

The Water Resources Development Act of 1986 (P.L. 99-662) prohibits any new interbasin diversion from the Great Lakes Basin unless it has been approved by the governors of each of the eight Great Lakes states. For purposes of administering this act, a consumptive water loss is not considered an interbasin diversion. A consumptive loss of more than 2 million gallons per day may have to be approved by the governors of the Great Lakes states and the premiers of the Great Lakes provinces.

The Great Lakes Charter requires that both interbasin diversions and consumptive losses of 5 million gallons of water per day averaged over any consecutive 30-day period are subject to review by the governors and premiers of the Great Lakes states and provinces. Because of this requirement, it is wise to establish historical water loss registration even if it is under the 5 million gallons per day threshold.

The Great Lakes Water Management and Conservation Act requires monthly reports of amounts of water "lost" as well as water withdrawn. Since the amount of lost water cannot be measured for outdoor water use, it must be estimated. DEC will estimate water loss based on the information supplied by the irrigator or the irrigator can estimate his own water loss. An acceptable way to estimate water loss is to use a method based on evapotranspiration (ET) rates during dry years. The method (see Table 2) is simplified in order to ease calculation and reporting. However, it is not precise enough to use in determining crop irrigation needs in a given year.

To estimate total monthly water losses, multiply the Great Lakes Basin ET values (Column 2) by the total acres irrigated (Column 3) and enter the result in Column 4. Compare these results to the total water withdrawals (Column 5) and report the values that are lower in Column 6. Enter these values in the last column of the third row in the Agricultural Irrigation Water Withdrawal Form. For example, the total maximum water loss for a 100-acre farm applying one inch of water in July would be 200 acre-inches (Column 4). Total monthly withdrawal (Column 5) is 100 acre-inches (see previous example). Since the number in Column 5 is less than the number in Column 4, estimated monthly water loss would be 100 acre-inches.

Table 2: Water Loss Calculation
Month Maximum
Area Irrigated
Total Maximum
Water Loss (col. 2 X col. 3)
Total Monthly Withdrawal
Estimated monthly
Water Loss
May 0.5
June 1.0
July 2.0 100 200 100 100
August 2.0
September 1.0
October 0.5
Other months 0.0

For Additional Help

Additional help in estimating water loss or completing registration forms can be obtained by contacting:

New York State Department of Environmental Conservation
Bureau of Water Resource Management
625 Broadway
Albany, New York 12233-3508
Telephone (518) 402-8099

This web page was prepared from a handbook developed with the assistance of the New York State Water Resources Institute and Cornell Cooperative Extension.

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