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Calculated Efficiencies <br />Efficiencies are used by StateMod in the calculated model to 1) determine total headgate or well <br />demand when IWR is provided as input; and 2) to determine the amount of unconsumed water <br />potentially returning to the river. Headgate or well demand is calculated on-the-fly as: <br />Headgate Demand = IWR <br />Average Calculated EfficiencysW, <br />Efficiencies of surface water structures used in the calculated model were developed using the <br />DMI demandts, along with the IWR information developed by the Consumptive Use Contractor <br />and records of historical headgate diversions. For every month of the simulation, estimates of <br />historical IWR are compared to actual headgate diversion to calculate an efficiency: <br />Calculated Efficiencys~ = IWR <br />Historical DiversionsW, <br />The monthly calculated surface water efficiencies are then averaged (by volume, not percent) <br />over the entire study period to provide 12 monthly average system efficiencies for each structure <br />as StateMod input. The calculated system efficiencies reflect both conveyance and on-farm water <br />losses. The command file to create calculated efficiencies is provided as Attachment 1. <br />In several areas of the San Luis Valley, a combination of application techniques is used to apply <br />water from groundwater wells. As such, groundwater efficiencies used in the surface water <br />modeling were determined by the Consumptive Use Contractor using the following approach: <br />GWerr = <br />(GW Lands Flood Irrigated) * 0.60 + (GW Lands Sprinklered) * 0.85 <br />Total Ground Water Land Acreage <br />Efficiencies for all structures types are incorporated into the direct diversion station (*.dds) and <br />well station (*.wes) files using the DMI demandts (seteff commands). <br />StateMod Calculated Demand Input File <br />As previously noted, StateMod allows a user to specify that demand information is either total <br />structure demand (values includes inefficient water use and losses) or crop irrigation water <br />requirement (IWR). In this latter case, actual demand that the model attempts to satisfy is <br />determined as IWR divided by the efficiency of the particular water source being used (i.e. <br />groundwater or surface water). <br />The Task 9 Surface Water Model includes calculated demands as a monthly IWR. This is <br />accomplished by specifying the variables idvcom and idvcomw with the value " 3" in the diversion <br />station (rgtwc.dds) and well station (rgtwc.wes) files, respectively. <br />Consistent with the control variable icondem set to 3 in the model control file (*.ctl), two demand <br />files, rgtwc.ddm, and rgtwc.wem are provided as model input. The rgtwc.ddm demand file <br />consists of IWR developed by the Consumptive Use Contractor (rgdss.ddc) for all structures of <br />StateMod type DIV and D&W, i.e. they receive surface water or surface and groundwater. This <br />file was created by eliminating all structures not of type DIV and D&W from the rgdss.ddc file. <br />1:09 PMC:Acdss\Task9-l.doc Calculated Demands October 23, 2000 -Page 2 of 3 <br />