PROJ00382

• Contract/PO #: C153685
• Contractor Name: Monument, Town of
• Contract Type: Loan
• Water District: 10
• County: El Paso
• Bill Number: SB 94-029
• Loan Projects - Doc Type: Feasibility Study

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Chapter IV - Formulation of Alternatives

Chapter IV - Formulation of Alternatives

Several alternatives were developed to meet the project purpose of rehabilitating the

Monument Lake Dam to meet SEO guidelineS. Alternatives were formulated to address the

problems described in Chapter I of this report, which include rehabilitating the: I) Spillway; 2)

Embankment; and 3) Outlet Works. An alternative was also developed to breach the dam and restore

the site back to natural conditions. The Town would like to gain back some of the reservoir storage,

which has been reduced by sediment, for recreational purposes including establishing a fish habitat,

therefore, a dredging alternative was also developed.

Figure IV-I shows the general configuration of the existing dam, outlet works, and
spillway. The existing spillway is located on the left abutment (east) as presented in the figure.
Access to the dam is obtained from the left abutment (east) through a public park area. Access to
the dam embankment is not readily available onc:e the spillway is discharging water.

A. Spillway Alternatives

Two alternatives were developed to rehabilitate the spillway at Monument Lake Dam.

Based on the hydrologic analyses performed for this study, the existing spillway control section

. is adequate to convey the required SEO design flood. The spillway control section does not

require rehabilitation. The downstream discharge chute at the base of the spillway control

section needs to be enlarged to convey the design flood safely away from the dam embankment.

The natural sandstone spillway chute also needs !O be protected from the erosive energy of the

design flood.

Spillway Alternative 81 - Riprap I Concrete Drop Chute

As shown in Figure IV-2, Alternative S I consists of multiple 4-foot high vertical drop

structures. The drop structures are constructed of reinforced concrete. The floor area of the chute

consists of2-foot thick 18-inch D50 riprap. The riprap is bedded on I-foot of sand. The chute is

uniform in width to develop a predicable flow into the stilling basin, which consists of grouted riprap

Monument Lake Dam Feasibility Study

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