C150163 Feasibility Study

• Contract/PO #: C150163
• Contractor Name: New Cache La Poudre Irrigating Company
• Contract Type: Loan
• Water District: 3
• County: Weld
• Bill Number: 04-1221
• Loan Projects - Doc Type: Feasibility Study

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Barnesville Equalizer

The Barnesville Equalizer dam can conservatively be classified as a Class III,
Small dam for which the required design storm is the 1 OO-yr storm. Based on the
hydrologic analysis, Barnesville Equalizer can store up to 3.5 times the design
storm without overtopping. Because it can store the design storm, Barnesville
Equalizer does not require a spillway. However, in order to ensure that the
maximum storage elevation is maintained at the decreed elevation, a 10-foot
wide overflow spillway and spillway channel are recommended. The spillway
used for the cost estimate consists of a 10-foot wide trapezoidal concrete cutoff
wall with 6(horizontal):1 (vertical) side slopes with riprap extending 10 feet beyond
the cutoff wall. The channel consists of an approximately 5-foot deep, 10-foot
wide trapezoidal earth-lined channel. Results of the preliminary hydrologic
modeling for Barnesville Equalizer are summarized in Table 7.

Table 7 - Barnesville Equalizer H
Dam Classification _
DesiQn Storm
Peak Inflow
Total Inflow
Peak Outflow
Peak StaQe
Required Spillway Length
1. Entire design storm inflow is stored in 0.3'.

drologic Modeling Summary
Class III, Small
100-yr
880 efs
67 ac-ft
o cfs
4670.3"
0'

Evaporation and Rainfall

The average annual evaporation at the site is approximately 38 inches and the
average annual rainfall is approximately 16 inches. The detailed hydrologic
modeling required to accurately predict the amount of runoff that will enter the
reservoirs throughout the year is beyond the scope of this study. In order to
obtain an upper bound for the amount of net loss due to evaporation, only rainfall
directly on the reservoirs was considered. Thus, ignoring runoff from the basins,
the net loss for each reservoir is 22 inches per year. If all of the reservoirs are
kept full throughout the year, there would be a maximum net loss of
approximately 859 ac-ft per year from the three reservoirs together.

North Side Lateral and North Side Extension Operational Study

Smith Geotechnical conducted an operational study of the North Side Lateral and
North Side Extension in order to determine the size of equalizer reservoir
necessary to improve system efficiency. The study compared water deliveries to
water demand for the section of the ditch system downstream of Turnout 31 over
a 6 year period from 1995 through 2000. The study showed that in five out of the
six years the total amount of water available downstream of Turnout 31 during
the season exceeded the total demand downstream of Turnout 31, but that on
several occasions the peak demands exceeded the available flow in the ditch. In

New Cache Feasibility Study

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