WSPC179

• File Number: 8240.200.49.J
• Description: Colorado River Threatened-Endangered - RIPRAP - Price-Stubb Fish Passage - Environmental Studies
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 4/1/1999
• Author: DOI-BOR
• Title: Draft Environmental Assessment - RE- Providing Fish Passage at the Price-Stubb Diversion Dam on the Colorado River - 04-01-99
• Water Supply Pro - Doc Type: Report/Study

001532

Chapter 3 - Affected Environment and Environmental Consequences

decrease in river flow and river velocity' would occur in the section of river between the diversion
dam and the discharge point of the power plant (bypass reach). This decrease would be
negligible during peak flows and the corresponding high scour velocities. The reduced velocity
during low flows might cause some increase in sedimentation in the bypass reach. This sediment
would be flushed annually during spring runoff,

Fish Ladder (with or without Hvdropower Plant): Impacts of building a power plant
and constructing a fish ladder around it would be similar to those of the No Action alternative.
No change in localized sedimentation during low flows is expected, since there is no bypass
reach in the power plant designs for this alternative.

Dam Removal: Dam removal would cause an increase in the water velocity upstream
from the dam. Reclamation's Technical Service Center conducted a hydraulic and scour analysis
of the project (Collins, 1999), Analysis results in Figures 5 and 6 show the estimated river
velocities with and without the dam. Figure 5 shows velocities for a 100-year flood; Figure 6 is
for comparison at a lower peak flow of 10,500 cfs.

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2,000 4,000 6,000
Distance upstream from dam (feet)

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_ with dam removed.-- with dam retained

Figure 5 - River velocity at 44,500 cfs

The velocity increase would be greatest at the dam and would gradually diminish upstream.
Existing angular riprap on the west bank of the river would be sufficient to protect the railroad
embankment from scour due to increased velocities upstre~ from the dam (Collins, 1999). At
the Colorado River Siphon, about 3,600 feet upstream from the dam, the difference in velocity is
negligible. Therefore, no increase in scour should occur at the siphon or further upstream.
Downstream from the dam, no change in river velocity is expected, and no increase in scour
should result.

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