RGDSS_Task3_ModelingEffortReview

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For ditches electing to store their foregone direct flow at Platoro, the amount storable is also limited to auser-defined percentage of the amount foregone. Each ditch electing to store water at Platoro is limited to the capacity of their individual storage account in Platoro and the maximum capacity for all individual storage accounts in Platoro. Water stored in Platoro by a ditch will be later released to the ditch when its direct flow rights are not adequate to meet the ditch demand. Step 3 -Closed Basin and Norton Drain Exchange The third step of the model operates an exchange of water into the General storage pool at Platoro Reservoir from water put into the Rio Grande River from the Closed Basin Project. The Closed Basin water allows Platoro to store when it would otherwise have to release or bypass to meet Compact obligations. The Closed Basin exchange is not dependent on the availability of actual Closed Basin flows at the time of the exchange. Instead, the exchange is a "non-real-time" exchange wherein the only important aspect of Closed Basin flows is the amount available for exchange over an entire year. Steps 4 and 5 - Storage Releases from the ISA and General Pools If a particular ditch is not entitled via its water rights to the entire amount of water needed, the model attempts to make water deliveries out of Platoro Reservoir to the ditch. In the forth and fifth steps of the model, water is released from the ISA and general pools in Platoro, respectively, depending on entitlement and availability of water. Ditches must use all of the water in their individual accounts prior to receiving water out of the general pool. This strategy allows for more widespread use of the general pool by junior ditches and will minimize the end of year transfer from the individual storage account pool to the general pool. Releases out of ISA accounts are limited to the amount put in by each ditch by foregoing diversions during an earlier time period in the same year. ISA releases are subject to a flow dependent transportation loss, but may be overridden in the model by a user defined loss percentage. Water in the general pool is allocated among the ditches on a first come -first served basis. At the end of each irrigation year, any unused water in the ISA pool is transferred into the general pool. 6 -Flood Control and Minimum Stream Flow Releases The sixth model step is when additional operations and accounting occurs related to flood control operations at Platoro Reservoir. Additional water releases may also be made to meet minimum instream flow requirements. There are three distinctly separate aspects to flood control at Platoro. There is a 6,000 acre feet flood control pool located from 54,000 to 60,000 acre-feet. This pool is never intentionally filled and is emptied as soon as possible. Currently this 6,000 acre-foot pool is not represented in the model. The second aspect of flood control involves springtime drawdown operations on conservation storage when the Army Corps of Engineers determines that not enough free space is present in the reservoir to capture the predicted runoff without flooding downstream users. The third aspect of flood control is the prevention of flows exceeding 2500 cfs at Magote and 1600 cfs at Las Sauces at all times. The second and third aspects of flood control are described below. Platoro is operated in the model in agreement with the Army Corps of Engineers 1963 Platoro Reservoir Flood Control Regulation Manual. This manual uses a standard COE Flood-Control Storage Reservation Diagram to specify reservoir drawdowns in the conservation pool from March 1 to May 9 based on (1) forecasted inflows up until July 31 and (2) current reservoir contents. The greater the forecasted inflows and the greater the current storage, the greater the drawdown. In extremely high years the curves call for Platoro to be drawn down to approximately 10,000 acre-feet. C:\cdss\Task3Mem.doc Review Previous Modeling Efforts Apri16, 1999 -Page 4 of 11