C150334 Feasibility Study

• Contract/PO #: CT2015-044
• Contract/PO #: C150334
• Contractor Name: McDonald Ditch Company
• Contract Type: Loan
• Water District: 20
• County: Rio Grande
• Loan Projects - Doc Type: Feasibility Study

Feasibility Study for the Plaza Project — Phase 2: McDonald Ditch Implementation Project
Section 5 - Existing Conditions
The project elements include the streambanks in the project area, a damaged wetland, and the
McDD diversion and headgate. The elements included in Phase 2 were identified as priorities for
restoration in the 2001 Study, the 2007 Watershed Strategic Plan, and the Plaza Plan.
5.1 Streambanks and Channel Current Condition
The 2001 Study area was broken into reaches based on homogeneity of geomorphic, hydrologic,
bed material, and man - influenced conditions. The project area is located within Subreach C1 of
Reach C (Figure 4).
The Rio Grande in this reach is primarily used for irrigation, wildlife habitat, ranching and
recreation. Reach C was ranked "poorest" in channel stability and condition of the floodplain, and
was identified as a high priority for restoration. Reach C is a moderate sloped, slightly entrenched,
cobble /gravel channel. The bed form is riffle /pool. Within Reach C, the following issues with
river function are present: inadequate floodplain function and connectivity; loss of flow control
and system stability; and high diversion maintenance caused by erosion and the accumulation of
debris and sediment. Specifically, the 2001 Study recommended that erosion and deposition
problems in the vicinity of the Sevenmile Plaza area be addressed. The fishery in the project area
is a transition zone between cold water and warm water fisheries. The main factors limiting the
extent and quality of the cold water fishery are dewatering, channelization, and aggradation. The
loss of water reduces the pool capacity, increases the water temperature, and provides for high
sedimentation rates - all detrimental to the primary cold -water fish, trout. Colorado Parks and
Wildlife does not manage for trout in the Project area due to lack of public lands, amount of
diversions, and presence of other competing landuses. Therefore, owners of private lands
assume the responsibility for the majority of habitat improvements.
11
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Figure d. Location of Reach C and Subreach CI (as designated by the 1001 Study)
and the Plaza Project - Phase 1
The Rio Grande in this reach is primarily used for irrigation, wildlife habitat, ranching and
recreation. Reach C was ranked "poorest" in channel stability and condition of the floodplain, and
was identified as a high priority for restoration. Reach C is a moderate sloped, slightly entrenched,
cobble /gravel channel. The bed form is riffle /pool. Within Reach C, the following issues with
river function are present: inadequate floodplain function and connectivity; loss of flow control
and system stability; and high diversion maintenance caused by erosion and the accumulation of
debris and sediment. Specifically, the 2001 Study recommended that erosion and deposition
problems in the vicinity of the Sevenmile Plaza area be addressed. The fishery in the project area
is a transition zone between cold water and warm water fisheries. The main factors limiting the
extent and quality of the cold water fishery are dewatering, channelization, and aggradation. The
loss of water reduces the pool capacity, increases the water temperature, and provides for high
sedimentation rates - all detrimental to the primary cold -water fish, trout. Colorado Parks and
Wildlife does not manage for trout in the Project area due to lack of public lands, amount of
diversions, and presence of other competing landuses. Therefore, owners of private lands
assume the responsibility for the majority of habitat improvements.
11