Resources Management

Aspinall Operations EIS

Navajo Dam and Reservoir

San Juan River Basin RIP Hydrology

Drought In The UC Region

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SJRIP Scenario Model Runs

The following table is an inventory of selected San Juan Hydrology Basin Model (SJHBM) runs that were made to analyze specific data and operating scenarios. Output data of more recent runs are available from Keller-Bliesner Engineering. Scenario runs have been used to analyze 3 major hydrologic studies which are the NIIP Consulation, the Animas LaPlata Supplemental Environmental Impact Study (ALP SEIS), and the Navajo Enviromental Impact Study (NEIS). NIIP Consulation runs were made with first generation models and rulesets. ALP SEIS runs were made with second generation models and rulesets. NEIS runs to date were made with second generation models and rulesets.

Within each major study, sub scenarios were run to evaluate system sensitivity and to make comparisons. During the NIIP Consulation study, the baseline depletions were being adjusted. This process included inclusion of 3000 acre-feet of unspecified depletions that the states felt should be included in the baseline. They are unspecified in that they are not associated with a specified entity. The 3000 acre-feet of unspecified depletions are in the present baseline depletions.

Another sub scenario that was tested extensively are various minimum releases from Navajo Dam. The minimum release mostly affects the flows between the Archuleta gage and the Animas River confluence on the San Juan River which is a prime trout habitat. The ones that are shown below are a 250 cfs year round minimum release, a 500 cfs year round minimum release, and a 400 winter minimum release with a 250 minimum release the remainder of the year. Essentially, when using the current baseline depletions and second generation hydrology, the 250 minimum release is the only scenario that meets the SJRIP Flow Recommendations.

Another sub scenario that was tested extensively was the operation of Navajo Dam to emulate historic operations. These runs were made to provide a baseline to which to compare flushing (flow recommendation) operations. Historic operations were emulated by developing a regresssion of runoff season releases to storage, last month's release, and forecasted inflow. The remainder of the year was operated to release the minimum of meeting downstream demands or 500 cfs.

The configuration and operation of ALP is another sub scenario that was tested. The first generation only removed ALP depletions from the model at appropriate locations. The second generation model operated ALP and included the ability to reduce pumping to increase downstream San Juan flows or to make supplemental releases to increase downstream San Juan flows. The latter behavoir did not provide benefits that were not offset by higher pumping requirements and a larger reservoir. The former criteria are both a functions of downsteam San Juan flows and Navajo Dam contents. Additional information on ALP operating criteria are available. Finally, different configurations of ALP were investigated. The locations of depletions supplied by ALP affect the size of Ridges Basin Reservoir, when supplemental releases have to be made, and the availability of return flows from ALP. The later NEIS runs were made with an ALP configuration that depletes all Indian water upstream of the New Mexico border.