# 3.3 - Water Supply Limited Crop Consumptive Use by Structure Considering Ground Water

If ground water information is available, the user can choose to consider ground water supply in the calculation of water supply limited consumption. Estimates of monthly historical surface water supply available to the crops, based on historical diversion records and maximum irrigation efficiency from the river to the crop, are input for each structure. In addition, estimates of historic monthly pumping can be input if available, or monthly pumping capacity can be input to limit the StateCU estimate of pumping. As described in Section 4.15, the annual time series input file provides the annual acreage under a ditch that is flood irrigated by surface water; sprinkler irrigated by surface water; flood irrigated by surface water and supplemented by ground water; and sprinkler irrigated by surface water and supplemented by ground water.

StateCU provides three approaches for considering both surface water and ground water supplies. The approach can vary by structure and by year, as defined by the variable gmode in the annual time series input file (see Section 4.15). Soil moisture accounting is as described in Section 3.2 for all approaches on acreage with a surface water source. If pumping estimates are not available, StateCU only estimates pumping to meet irrigation water requirement; excess ground water is not withdrawn to fill the soil moisture reservoir. If a historical pumping file (*.pvh) is provided with the model scenario, excess ground water will be used to fill the soil moisture reservoir if storage is available. Total well capacity defined for the structures in the irrigation parameter input file is distributed to ground water sprinkler and ground water flood lands based on acreage. If pumping estimates are provided to StateCU, they are distributed to ground water sprinkler and ground water flood lands in proportion to remaining crop demands. Note that if pumping estimates are provided in the historical pumping file (*.pvh), then the well capacity assigned in the irrigation parameter file is not used. Missing surface water supply is handled as described in Section 3.2, with the surface water portion of supply estimated through proration.

gmode= 1 - Maximize Supply Approach:

The following sequence is used to maximize available surface water and ground water supplies by ditch system. This approach allows demand for irrigated parcels within a ditch system served by sprinklers to be met by available ground water and allows parcels without a ground water supply to have first ‘priority’ for available surface water.

1. Ground water is pumped to meet the irrigation water requirement on sprinkler irrigated acreage identified as having a ground water source using the maximum sprinkler efficiency, limited by the acreage-prorated permitted pumping capacity.
2. Surface water is applied to meet the irrigation water requirement for acreage without a ground water source at the appropriate application efficiency (prorated based on the flood irrigated surface water acreage and the sprinkler irrigated surface water acreage).
3. Any remaining surface water is applied to meet the irrigation water requirement for flood irrigated acreage identified as having a ground water source at the maximum flood irrigation efficiency.
4. Any remaining surface water goes to soil moisture storage or is available for return flow.
5. Ground water is pumped to meet any remaining irrigation water requirement on flood irrigated lands identified as having a ground water source using the maximum flood efficiency, limited by the acreageprorated permitted pumping capacity.

gmode= 2 - Mutual Ditch Approach:

The following sequence is used if the ‘mutual ditch’ approach is chosen. This approach provides equal shares of surface water to all acreage under a ditch system, regardless of application method or whether individual parcels also have the ability to use ground water.

1. Surface water is applied evenly to all acreage under a ditch system to meet the total irrigation water requirement.
2. Ground water is pumped to meet any remaining irrigation water requirement on sprinkler irrigated acreage identified as having a ground water source using the maximum sprinkler efficiency, limited by the acreage-prorated permitted pumping capacity.
3. Ground water is pumped to meet any remaining irrigation water requirement on flood irrigated acreage identified as having a ground water source using the maximum flood efficiency, limited by the acreageprorated permitted pumping capacity.

gmode= 3 - Mutual Ditch Approach with Ground Water Pumped to Meet Sprinkler Acreage Irrigation Water Requirements:

The following sequence is used if the ‘mutual ditch’ approach is chosen, but sprinkler irrigated acreage use ground water to meet their irrigation water requirements. This approach allows surface water shares to be available for recharge, if a ground water supply is available to meet crop demands, even if irrigation water requirements on lands only using surface water are not met.

1. Surface water is allocated to all acreage under a ditch system. Acreage served only by surface water or flood irrigated acreage with available ground water apply their share of surface water to meet irrigation water requirements.
2. Ground water is pumped to meet irrigation water requirement on sprinkler irrigated acreage identified as having a ground water source using the maximum sprinkler efficiency, limited by acreage-prorated permitted pumping capacity. Surface water shares for this acreage are made ‘available for recharge’.
3. Ground water is pumped to meet any remaining irrigation water requirement on flood irrigated lands identified as having a ground water source using the maximum flood efficiency, limited by acreageprorated permitted pumping capacity.