BOARD01208

• Board Meeting Date: 5/23/2005
• Description: CF Section - New Project Loans Bijou Irrigation District - Empire Reservoir Dam Rehabilitation
• Board Meetings - Doc Type: Memo

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Bijou Irrigation District
May 24-25, 2005

Agenda Item 150

Alternative 3, Construct a new spillway and place new toe drains in the Outlet and McIntyre .
Dams - This would include constructing a spillway capable of passing storm flows in accordance
with the requirements outlined by the SEO, and address the embankment stability concerns as
required by the SEO by installing a seepage collection system on the dams. The Outlet and
Mcintyre Dams have seepage collection ponds at the toe of the embankments. No record or
physical evidence of any existing toe drains in the Outlet and Mcintyre Dams that discharge to the
collection ponds, could be found. The East Dam has working toe drains that were installed in the
mid-1980s. As-built records of these drains are available for review. Based on groundwater levels
additional seepage control work on the East Dam not currently proposed. Alternative No.3 appears
to address each area of concern voiced by the SEO, and therefore was selected.

Selected Alternative 3, Construct a new spillway and place new toe drains in the Outlet and
McIntyre Dams - The project will involve the construction of a spillway with a crest elevation of
gage height 30 feet. The spillway design is based on an Infiow Design Flood (IDF) that is 75% of
the Probable Maximum Flood. The spillway and outlet works will provide drawdown from the IDF
maximum stage of GH 32.6 to GH 30.0 in 5 days, as required by the SEO. Additionally,
approximately 4,400 linear feet total of toe drain is to be constructed at the Mcintyre and Outlet
embankments. Each of the toe drains will have manholes at regular intervals for inspection and
future location confirmation. A Parshall Flume'will be installed at each toe drain outfall to quantify
discharge and seepage flow rates. The spillway will have a concrete crest and two concrete drop
structures. The main channel will be grass-lined with riprap reinforcing at key areas for hydraulic
stability. The spillway will be located at the Outlet embankment and will outfall into the main outlet
channel.

The Total Project cost is estimated to be:

.

1.
2.

Construction & Contingency
Engineering and Inspection
TOTAL

$ 630,000
110.000
$740,000

The final design is nearly complete and is expected to be submitted to the SEO in May 2005.
Pending final design approval by the SEO, construction would is planned to competed in October
2005, to be ready for winter filling on November 1.

The BID and the engineer believe no environmental permits will be required. All work is to be
associated with agriculture and all work is confined to the BID property. The Corps of Engineers
will be contacted concerning 404 permitting, but it is anticipated at this time thatjhe work either be
categorized as exempt or will fall under nation wide permits and no additional permitting will be
necessary.

Financial Analvsis

The total estimated cost of the project is $740,000 and BID water usage is 100% agricultural. Staff
is recommending a maximum loan amount of $666,000 (90% of the estimated project cost) for 30
years at an interest rate of 2.50%. BID will pay the additional 1 0% ($74,000) of the project cost
from reserve funds. BID will cover any costs that exceed the estimated project cost.

Table 1 is a summary of the financial aspects of the project. A CWCB Loan of $666,000 would
have an annual payment of $35,002 (including the 10% reserve requirement) at the loan terms of .
2.50% for 30 years. The CWCB loan will be repaid from increases in the tax levy from $10 per acre
to a minimum of $12 per acre. The annual loan cost for the project will be $1.76 per acre-foot
based on an annual delivery of 19,900 acre-feet to BID irrigated lands.

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