October 2009 - South Tahoe Public Utility District

This component is not anticipated to be affected by existing regulations and no additional
permits are anticipated with the implementation of this project. Capacity and stability
improvements would increase the system‟s overall reliability with regard to uninterrupted
conveyance of recycled water and limit potential operational constraints.
While the Diamond Ditch is the primary conveyance mechanism of the District‟s recycled water
system, the District must consider the issue of capital investment for improvements to the
Diamond Ditch which is owned by others.
9.6 Project No. 6 - Waterfall Pipeline Forebay and Pipeline
This project addresses the purpose and need statements:
PN-7. Operational control of the distribution system is insufficient.
PN-8. The Diamond Ditch conveyance capacity currently does not meet the on demand
recycled water flow rate of 25 cfs of the agreement between the District and the
Contractor Irrigators. Additionally, the District does not have control of the Diamond
Ditch.
If a recycled water piping system were constructed on the lands west of the West Fork of the
Carson River (See Project No. 8, page 9-72), the system would require pressure flow conditions
that would be generated by the hydraulic head differential of the Waterfall Pipeline and Forebay
(see Figure 9.3, at the end of Section 9). The untapped benefit of the elevation differential is one
of two principal concepts of the Waterfall Pipeline. Two of the District‟s objectives are satisfied
by this project. Development of the Waterfall Pipeline allows for a more efficient and flexible
system through the utilization of higher head as well as eliminating the operational constraints
caused by Bar Screen No. 5.
A forebay is necessary for the operation of the Waterfall Pipeline as a pipeline entrance facility.
The Waterfall Pipeline requires a sedimentation forebay and bar screen to minimize pipeline
maintenance and lengthen the service life of the pipe. If the bar screen becomes blocked the
water level will increase in the open ditch section of the Diamond Ditch and eventually spill. The
purpose of a forebay is to allow for some flow attenuation and an alarm system will warn the
District of a potential spill situation. The alarm is intended to notify District operations staff so
they can reduce the release from Harvey Place Reservoir and/or service the forebay.
9.6.1 Project Description
The Waterfall pipeline is planned to run from the northwest corner of Wade Valley to the Bar
Screen No. 5, a distance of approximately 1,900 linear feet. The alignment is planned to parallel
the Diamond Ditch alignment for a distance, then along the Diamond Valley Road to avoid the
existing waterfall section and finally to Bar Screen No. 5.
The forebay would be a cast in place concrete structure approximately 10 by 10 feet in plan
dimension. The depth of the box would be sized to allow for sediment capture, a rising water
service level to trip an alarm and a side outlet overflow weir that would direct spillage to the
Upper Celio Dressler Ditch, as opposed to the West Fork of the Carson River in the present
condition.
The total conceptual cost for the Waterfall pipeline and forebay project is $2.0 million. This cost
includes a concrete junction box, site preparation, and piping. Additional costs associated with
South Tahoe Public Utility District
Recycled Water Facilities Master Plan - October 2009 Page 9-70