3.4 - Water Supply Limited Crop Consumptive Use by Structure and Priority
There are often several water rights used to irrigate acreage associated with a structure. StateCU allows a user to define a single administration number to differentiate senior water rights from junior water rights. StateCU also allows the administration number to reflect historic call data on a monthly or daily time step. Consistent with Colorado water law, water supply limited crop consumptive use by priority first assigns diversions to senior priorities and then to junior priorities. In addition, an ‘other’ category of river diversions is used in the analysis to reflect diversions (and associated depletions) that exceed the decreed water rights associated with a structure or farm supplies not diverted at the river (supplied in the drain file, *.dra). The water coloring junior or senior to a user-defined administration number is maintained through the consumptive use analysis, including water placed and withdrawn from soil moisture.
If the user chooses to consider soil moisture in the analysis, as described in Section 3.2, water is stored in separate soil ‘accounts’ (senior, junior, other) based on the priority of the water diverted. If excess senior water is available to the soil reservoir and the soil reservoir is full, junior water will be ‘spilled’ to make room for the senior water. There are two options in the model control file (*.ccu) for extracting water from the soil zone to meet crop demands: based on proration and based on priority. If the proration option is selected, water is extracted from the soil zone from the senior, junior, and other ‘accounts’ in proportion to the amount of water in each account. If the priority option is selected, senior water is used first to meet crop demands.
If the user chooses to prorate consumptive use for structures with missing water supply data, as described in Section 3.2, historic diversions are estimated by dividing the prorated water supply limited consumptive use by the use efficiency associated with the structure. This estimated water supply is then distributed into water right priorities based on the water rights associated with the structure. Detailed water budget output produced by the program indicates whether water budget terms were ‘Calculated’ or ‘Prorated’.
Because the total monthly diversion used in the water-supply limited calculation may not reflect junior water rights that are in priority only a portion of the month, StateCU allows daily diversion to be used to determine the percent of monthly diversions that are senior or junior to the input administration numbers(s).