WSP00691

• File Number: 8142.700
• Description: Trinidad Project - Annual Operating Plans and Reports
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 12/1/1996
• Author: US DoI BoR
• Title: Review of Operating Principles and Project Operations Final Report
• Water Supply Pro - Doc Type: Operating Principles/Plan

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

r', (" ~:~' ,.
~I,)..J'-

one-for-one exchange at Trinidad Reservoir and the Las Animas gauge.

A review of the amendment to the operating principles for allocation of the excess storage

space and filling said space reveals that the one-for-one exchange at the Las Animas gauge and

Trinidad Reservoir is potentially a benefit to water users downstream of the confluence of the

Purgatoire and Arkansas Rivers. The amount of the potential benefit, as an increase in water

supply, is in the amount of the transit loss difference in the four miles of the Arkansas River from

the Las Animas gauge to the mouth of the Purgatoire River and the transit loss that would occur

in the 160 miles of the Purgatoire River from Trinidad Dam to its mouth.

The one-for-one exchange should be the net amount at the confluence of the Arkansas and

Purgatoire Rivers as determined by the Colorado State Engineer. The United States Geological

Survey's Livingston method for determination and assessment of transit losses by the Colorado

State Engineer was approved for delivery of exchange water in the Arkansas River from its source

to the Las Animas gauge. This same method should be used for determination and assessment of

transit losses for delivery of water in the Arkansas River from its source to the point of the one

for one exchange at the confluence of the Arkansas and Purgatoire Rivers. The United States

Geological Survey is currently conducting a transit time and loss study for regulated flows in the

Purgatoire River from Trinidad Reservoir to its mouth. If this study results in a methodology that

can be used and adopted by the Colorado State Engineer for administration of water rights and

distribution of water in the Purgatoire River, it should be used for determination and assessment

of transit losses for a one for one exchange at the confluence of the Arkansas and Purgatoire

Rivers. Otherwise, the Colorado State Engineer should either use existing or develop a suitable

methodology for determination and assessment of transit losses in the Purgatoire River from

15