C150008 Feasibility Study

• Contract/PO #: C150008
• Contractor Name: Leroux Creek Water Users Association
• Contract Type: Loan
• Water District: 40
• County: Delta
• Bill Number: HB 95-1155
• Loan Projects - Doc Type: Feasibility Study

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This would indicate a storage volume of approximately 800 acre-feet.

Appendix D contains a copy of the reservoir storage data taken from the SEO records. Appendix
E contains a copy of the recorded decrees for Carl Smith Reservoir and all enIargements,

NEED FOR THE PROJECT

The Carl Smith Darn experienced a structural slide near tlle right abutment on May 2, 1998 which
caused a breach in the dam near the 6-inch outlet. The breach in the dam occurred while the dam
was full and spilling and released approximately 500 acre-feet of the 800 acre-feet of water stored
in the reservoir.

This breach is discussed in detail in a report prepared for the State Engineer by Mr. Jim Norfleet
and Mr. George Van Slyke, both of the State Engineer's Office. The breach was also evaluated
in a study included in Appendix I of this report. Photographs of the darn and the breach are
included in Appendix A of this report.

Due to the breach created by the slide, the State Engineer has required the reservoir be emptied
and a designed breach be constructed to limit the reservoir to essentially zero storage. This breach
is outlined in Appendix I and is approximately 50-feet in depth with 2.5 to 1 slopes.

It is the intent of the Leroux Creek Water Users to rebuild the dam to an elevation that will allow
at least partial storage and allow the continued use of this dam for storage and as an equalizer.
To accomplish this, the Association has begun the process to evaluate the alternatives for
rebuilding the darn which are outlined in this report.

AL TERNA TIVES EVALUATED

A range of alternatives were considered including 1.) breaching the dam, 2.) rehabilitation to
elevation 8242 feet which is 10 feet lower than the existing darn crest, 3.) rehabilitation to
elevation 8252 feet which is the elevation of the existing dam crest, and 4.) raising the dam crest
to elevation 8267 feet which is 12 feet higher than the existing dam crest. The following
summary describes the work proposed for each alternative.

Alternative 1 - Dam Breach. This alternative is to permanently breach the darn whereby the
temporary breach that was constructed in the fall of 1998 is enIarged to a bottom width of 40 feet
to allow passing the 100-year storm. The breach side slopes will be 2.5 horizontal to 1 vertical
and the bottom elevation will be at 8202 feet. The discharge channel will be partially riprapped
for erosion protection and the side slopes of the breach seeded with grass. The reservoir surface
area will have to be seeded to prevent transport of silt by water and wind.

Figure 2 shows the cross section of the breach and the details of the work proposed.

Carl Smith Dam Feasibility

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