FLOOD11759

• County: Mesa
• Stream Name: Bosley Wash
• Basin: Colorado Mainstem
• Title: Bosley Wash Drainage Master Plan - Phase 2: Alternative Drainage Facility Evaluation - Draft
• Date: 11/1/2002
• Prepared For: Bosley Wash Watershed, CWCB
• Prepared By: HDR Engineering, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

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,iJo,sley Wash DTflinase Master flan
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Phase2: Alternative Drainage Facility Evaluation

importantly, the area represents an opportunity to achieve major reductions in
downstream flood discharges. In addition, the relative lack of development and the steep
terrain make the cost of land and the potential future impacts of construction .low.

Large vond ovtion:
The largest of the identified pond options provides 75.5 AF of storage and reduces
the downstream discharge into Bosley Wash to 50 cfs. This discharge was small
enough to reduce the potential overtopping of the downstream channel sections
and flooding above the Government Highline Canal. The cost of the facility,
including property acquisition costs, is estimated to be $1.15 million.

Intermediate pund optiut7. A. .
An intermediate pond option has been identified which provides 63.5 AF of

storage and reduces the downstream discharge to 100 cfs. The cost of the facility,

including property acquisition costs, is estimated to be $980,000.

Intermediate vond option B:
Another intermediate pond option consisting of 57.5 AF of storage and reducing

the downstream discharge to 150 cfs was developed. The cost of the facility,

including property acquisition costs, is estimated to be $900,000.

Smallvond option:
A final option for this location was evaluated. This option, the smallest of those
considered, provided a storage volume of 48.5 AF and reduced the downstream
discharge to 300 cfs. The cost of the facility, including property acquisition costs,
is estimated to be $775,000.

3.2 Improved Channel Capacity

Improving channel capacity represents another alternative for reducing flood damages. In
most cases, the enlargement of channels could be accomplished by excavating a small
amount of material from the channel bottom and banks and using that material to build up
the top of the channel banks. This prevents overtopping and the spilling of flood waters
onto adjacent properties or onto properties further downstream. For purposes of design,

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Page 11

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