PROJ00060

• Contract/PO #: C153721
• Contractor Name: Lyons, Town of
• Contract Type: Loan
• Water District: 5
• County: Boulder
• Bill Number: SB 96-153
• Loan Projects - Doc Type: Feasibility Study

.:

.

4~-6VL2A ITEJ.-f ISC<..
N"OV. 7, / 99.~

'-

Task 3. Diversion Dam and Raw Water Intake Structure

Town staff has operated the existing intake structure for many years. Initial site visits
and discussions with the Public Works Director have fixed the scope of the design of these
facilities. The existing diversion dam is to be demolished and rebuilt as a new structure. The
existing presedimentation basin will be cleaned and substantially modified for more efficient .
operations. All new structures must be designed to maintain sufficiently high velocities to
transport stream sediments dO~llStream through the diversion dam. The headworks will require
a trash rack and the design must exclude bedload sediments from entering the presedimentation
basin and grit channel. The da.TJl structure is considered non-jurisdictional under the regulations
of the Colorado Division of Water Resources.

RBD, Inc. conducted a hydrologic analysis of this portion of North St. Vrain Creek in 1991 for
the Apple Valley Road Bridge Project. It has been determined that much of the data generated in
that project Vvill be of use in the task.

Allowances must also be made for: demolition of the existing structures, bypass flows,
transmigration of fish, temporary intake to the raw water transmission line during construction,
passing of flood waters and wintertime icing conditions. Recreational uses may also have to be
considered. This task is accomplished in the follO\ving steps:

3.1 Conduct site topographic and geotechnical site surveys. Prepare a topographic site plan of
the existing conditions, to be used in the permitting process and the final bidding documents.
Prepare a geotechnical report to include design criteria for the foundation design and
construction of a new diversion structure and reconstruction of the existing presedimentation
basin. Analyze existing hydrology data to determine the anticipated maximum design flood over
the diversion structure. Prepare hydraulic design criteria to accomplish the functions outlined
above, such as allowances for sediment transfer, minimum flows and fish passage. Combine the
findings of these investigations and preliminary design considerations in a preIiminary design
report, to include site plan, permitting requirements, sketch designs and opinion of probable cost,
for review by the town staff.

3.2 After review by tOVvTI staff; prepare development design drawings (DD) of the proposed
improvements: diversion dam, presedimentation basin, inlet gate and high water protection
barrier.

3.3 Prepare an application for and assist the town in the processing of a Section 404 permit for
construction in the river corridor.

3.4 Prepare final design and bidding documents (ED) for construction of the elements in subtask
3.1,3.2 and 3.3 above. Prepare an engineer's estimate of probable construction cost.

4