C150094 Reservoir Inflow Addendum

• Contract/PO #: C150094
• Contractor Name: La Plata Water Conservancy District
• Contract Type: Grant
• County: La Plata
• Loan Projects - Doc Type: Report

SZSI
Wright Water Engineers, Inc.
1666 N.Main Ave.,Suite C www.wrightwater.com
Durango,Colorado 81301 December 20,2002 e-mail:[e-mail]
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Via Hand-Delivery
Brice Lee
La Plata Water Conservancy District
981 County Road 122
Hesperus, CO 81326
Re: Red Mesa Reservoir Enlargement Hydrology—Reservoir Inflow Addendum
Dear Brice:
This report addendum is to provide further study on the Wright Water Engineers, Inc. (WWE)
August 2002 preliminary estimate of inflows to Red Mesa Reservoir. The subject work includes:
1. An increase in the period of record from a study period of three years (1996-1998) to a
study period of 10 years (1989-1998).
2. A more thorough analysis of the historical demands and inflows in the La Plata River
Basin using actual diversion data, gauge data for the La Plata River and its major
tributaries and the administrative record for the New Mexico Compact demands.
3. A mass balance analysis of the river basin to measure ungauged inflows and outflows.
The analysis is limited to filling the enlarged Red Mesa Reservoir over the November through
September period with the reservoir being emptied each October.
STUDY PERIOD
The original model developed for the Red Mesa Reservoir Study was based on decreed water
rights and historically measured inflows in the basin using a daily time step over a three-year
period of record (1996 through 1998). To add reliability to the analysis, the period of record was
extended to 10 years (1989 through 1998), and a monthly time step was used. The change from
a daily time step to a monthly time step did not change the accuracy of the reservoir inflow
analysis.
The 1989 through 1998 time period was selected based on availability of measured flow data.
The reported gauge data for Long Hollow and Cherry Creek began in October of 1988. The total
annual discharge of water measured at the Hesperus Gauge between 1989 and 1998 is shown in
Table 1. The 10-year average flow over the 1989 through 1998 period was approximately
30,000 acre-feet (af) of water. The average flow over the 83-year period of record was 32,246
af, and the median flow was 31,406 a£ The average flow over the 10-year study period (1989-
1998) was 30,061 af, and the median flow was 26,139. The 10-year period of record selected for
DENVER GLENWOOD SPRINGS
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