FLOOD10357

• Document ID: 123
• County: Rio Grande
• Stream Name: Alamosa River
• Basin: Rio Grande
• Sub-Basin: Alamosa - Trinchera
• Water Division: 3
• Title: Alamosa River Watershed Project Literature and Watershed Assesment, Final EPA Report
• Date: 9/30/2003
• Prepared For: Valle del Sol Community Center
• Prepared By: US Environmental Protection Agency
• Watershed Pro - Doc Type: Project Report

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ditch diversions (Figure 7) are located throughout the lower portion of the watershed,
primarily from Gunbarrel Road and east near US 285. These headgate structures are
critical in acquiring water from the river to support agricultural activities.

In the Upper Portion of the Watershed, the USFS applied for and was granted reserved
water rights in the Rio Grande National Forest in the State of Colorado Water Division
NO.3. This includes the Upper Alamosa River Watershed, from the headwaters to the
National Forest Boundary. Instream flows were decreed to the Rio Grande National
Forest in 2000 for:

. Maintaining, improving, protecting, and minimizing damage to the following:
(1) Riparian ecosystems, which includes stream dependent wetlands;
(2) The natural physical function of stream channels;
(3) Viable and diverse populations of fish and wildlife, including all habitat
necessary for such populations;
Scenic and aesthetic conditions and values;
(4) Public opportunities for outdoor recreation;
(5) Soil conservation and preservation of the quality of soil resources;
. Range uses; and
. Prevention and control of forest fires.

The Quantification Point (QP) for quantifying flows is the Alamosa River at the
downstream of the Nation Forest Boundary above Terrace Reservoir. Flows are
quantified for two periods:

1. During the period of annual snowmelt runoff: When natural flow reaches the minimum
highflow" the U.S. has the right to receive at, and upstream of, its QP all flow up to and
including the flow equal to the maximum high flow, until such time as the natural flow
decreases below the minimum highflow. The maximum highflow is defined as the upper
limit of the flows to which the U.S. is entitled during the runoff period, and is flow equal to
the highest instantaneous flow historically occurring, on average, once in every 10 years.
This correlates to a flow equal to two times the Q1.5 flow (flow with a return period of 1.5
years, or roughly the bankfull flow). The minimum highflow is the lower limit of flows to
which the U.S. is entitled during the runoff period, and is a flow equal to 60% of the Q1.5
flow.

2. Baseflows: For times outside of the period of annual snowmelt runoff, the U.S. has
the right to receive at, and upstream of, its QP baseflows equal to:

· January, February, March and December: Flow available in priority up to a
flow equal to the Median Monthly Discharge rate for that month.
· April through November: Flow available in priority up to a flow equal to 80%
of the Mean Monthly Discharge rate for that month.

All of these appropriated flows for the USFS are shown below:

Minimum Maximum Jan Feb Mar Apr May June July Aug Sep Oct Nov Dee
Hiah Flow Hiqh Flow
222.78 742,6 20,6 23,5 29,7 68,9 178.2 134,8 56.4 43.3 27,0 23.4 19.3 22,0

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