PROJ02037

• Contract/PO #: PO 060000000018
• Contractor Name: Orchard Mesa Irrigation District
• Contract Type: Grant
• Water District: 0
• Loan Projects - Doc Type: Feasibility Study

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Task 1 Results - Orchard Mesa Power Canal enlargement study

4

Section 4 - Open Earthen Canal 50+00 to 57+87. No plans were found for this portion
of ditch. However, during a field visit the canal was observed flowing at a flow rate of
approximately 800 cfs. Freeboard along much of this section of canal was observed in
excess of 3 ft. In order to increase the capacity of this ditch from 800 cfs to 860 cfs, little
work will need to be done. For the purposes of cost estimation, it was assumed that
some fill would be required in low spots.

Section 5 - Mann Gulch Siphon 57+87 to 59+40. The existing Mann Gulch siphon is
designed to convey a flow rate of 800 cfs. In order to increase the capacity of this
structure, the inlet and outlet works would need to be raised by about 1.5 ft.

Section 6 - Open Earthen Canal 59+40 to 72+50. No plans were found for this portion
of canal. During a field visit, this section of canal was observed flowing at a flow rate of
800 cfs. Freeboard along the canal was observed in excess of 3 ft in many places.
There was also a bridge crossing along this section of canal. The bridge's low girder
elevation was at least 2-ft above the water surface. This section on canal will likely
require little, if any, modification to handle an additional 60 cfs of flow. For cost
estimation purposes, it was assumed some fill would need to be imported and placed
along some sections of the existing canal.

Section 7 - Stokes Gulch Siphon 72+50 to 74+16. The existing Stokes Gulch siphon is
designed to convey a flow rate of 800 cfs. The capacity of this structure could be
increased to 860 cfs by increasing the top elevations of the inlet and outlet works by
about 1.5 ft.

Section 8 - Flume Section 74+16 to 78+50. The existing flume, similar to the flume
immediately downstream of the Colorado Siphon, has a capacity of 812 cfs. The flume
was observed in the field, operating at a flow rate of approximately 800 cfs. The average
freeboard was about 1 ft. The tops of the concrete walls on the existing flume would
need to be raised in elevation by 1.5 ft to account for extra depth in the flume caused by
the increased flow rate.

Section 9 - Cut and Cover Conduit 78+50 to 93+50. The Cut and Cover Conduit is an
11' wide by 11'-4" deep box conduit. It has a design flow rate of 800 cfs. Under the
design flow rate of 800 cfs, the box flows at a depth of 10ft 4 in. If the flow rate was
increased to 860 cfs, the conduit would operate very close to the maximum box conduit
depth of 11 ft 4 in, though it is considered that the existing conduit is likely adequate to
handle 860 cfs. The inlet and outlet top elevations will need to be raised by 1 to 1.5 ft in
elevation to prevent overtopping.

Section 10- Flume Section 93+50 to 97+71. The existing flume has the same geometry
and design flow rate as does Section 8. The design flow rate is 800 cfs. Under the
design flow rate, the canal runs with an average of about 1 ft of freeboard. In order to
increase the capacity of the flume to 860 cfs, the tops of the concrete flume walls would
need to be increased by 1 ft. A small bridge also exists along this section of canal, and it
may need to be modified slightly to make room for the higher canal walls.

2616-R1

Orchard Mesa Irrigation District

Water Management Consultants