WSP05236

• File Number: 8220.106
• Description: Animas-La Plata
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 2/26/1996
• Title: Final Biological Opinion - 1996
• Water Supply Pro - Doc Type: Biological Opinion

(M&I) benefits if an annual depletion of the project is limited to
57,100 AF.

The design capacity for the Durango Pumping Plant under the 57,100 AF
scenario is 70 cfs. This means that under full operating head (full
reservoir) the pumps can pump 70 cfs, but when there is not full head
(reservoir not full) the pumps can pump up to 79 cfs. This reduces
the peak withdrawals during high streamflow months compared to the
1991 proposal. The hydrologic effects of these changes in the model
are very minor with respect to San Juan River flows at Farmington,
Shiprock, and Bluff. A separate hydrologic model of Animas and La
Plata drainages incorporated these changes. Output from this model
was then applied to the entire San Juan Basin model.

2. Minor San Juan Basin Depletions under the SJRIP

As part af the RIP, minor depletions up to a total of 3,000 AF are
allowed in the basin prior to the completion of the 7-year research
period. Since 1991, these depletions have consisted largely of small
private uses and now total about 1,500 AF. Although these actual
points of diversion are known, due to the small quantities involved
and the difficulty in tying them to specific nodes in the model,
one-third of this total was assumed to occur above Navajo Dam and
two-thirds just below Farmington. This represents an over
conservative assumption but since the depletions quantities were
small, this simplification will not materially affect the projected
flows at the three San Juan River gages. The total depletion of
these uses will average less than 3 cfs through the year.

3. Navajo Indian Irrigation Projects (NIIP) Blocks 7 and 8

Since the 1991 Opinion was issued, the NIIP has received section 7
clearance for construction of facilities to deliver water to lands
served by Blocks 7 and 8 of NIIP. No additional depletion of San
Juan River Basin water resulted since baseline depletions associated
with the Hogback and Fruitland diversions were exchanged for the
additional NIIP depletion. Water for NIIP was delivered out of
Navajo Reservoir through the existing NIIP canal headworks. This
diversion was modeled accordingly.

4. Reduction of Dolores River Basin Return Flows into McElmo Creek

The potential to reallocate additional water supplies for instream
flow purposes below McPhee Dam on the Dolores River has resulted in a
modification of the expected transbasin diversions out of the Dolores
Basin into the San Juan Basin. Consequently, the return flows from
this irrigation water will also decrease.

The nature of the decrease in diversions is tied to the instream flow
needs below McPhee Dam. During dry years, additional releases are
desired to maintain the trout fishery immediately downstream of the
dam. Rather than allocate additional supplies in all years, a

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