C153857 Feasibility Study

• Contract/PO #: C153857
• Contractor Name: Western Mutual Ditch Company
• Contract Type: Loan
• Water District: 2
• County: Weld
• Bill Number: SPL
• Loan Projects - Doc Type: Feasibility Study

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Western Mutual Diversion Repairs and Improvements
eWeB Feasibility Study
May 6, 1998 (Revised December 29, 1998)

Check Replacement Alternatives Evaluated

A range of alternatives for replacement of the check structure were considered including: 1) Don't
repair or replace the check structure, 2) Repair the check structure, saving as much of the old
structure as possible, and 3) Replace the check with a new structure, Three types of construction
for the third alternative were investigated including, a) a concrete check wall with riprap stilling
basin, b) a sheet pile check wall with riprap stilling basin, and c) a 10:1 sloping riprap drop. A
fourth alternative, a 4: 1 grouted riprap drop was proposed by the Natural Resources Conservation
Service. However, because the grouted section is inflexible, and otherwise the construction is the
same as the 10: 1 sloping riprap drop, this alternative was not considered further.

The concrete and sheet pile drops with riprap stilling basin are exactly the same except for the type
of construction used for the vertical wall of the drop. The sloping riprap drop requires the same
type of upstream wall structure, in order to accommodate flashboards and the low flow notch, but
does not require the same thickness of riprap in the stilling basin. The thickness of the sloping
riprap drop is three feet. Appendix D contains preliminary design information for the steel sheet
pile vertical drop.

A subjective evaluation of the check replacement alternatives follows:

1. Don't build the project:

Shareholders would be unable to irrigate 7,280 acres of crop land. Crops irrigated
by the Ditch Company are valued at $7,010,980 and could not be produced
without irrigation water, As a comparison, the income from 7,280 acres of pasture
at $90 per acre (figure provided by the Ditch Company), conservatively assuming
that the current income from irrigated pasture could be generated on unirrigated
land, would be $655,200 or less than 10 percent of the income from irrigated crops.

2. Repair the existing structure:

The old check structure is damaged beyond repair. There is not enough sound
structure remaining to serve as a basis upon which to repair. This alternative is not
technically feasible.

3, Replace the old check structure with a new structure:

There must be a functioning check structure in the south channel for the Western
Mutual Ditch Company to be able to divert reliably at its headgate. Otherwise, the
south channel may become the main channel of the South Platte, it's flow bypassing
the ditch headgate and reducing the ability of the Ditch Company to divert water. A
new structure will immediately enhance the ability to divert and in the future will
help maintain the course of the river by reducing the frequency of flows in the south
channel.

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