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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Bosley Wash Drainage Master Plan
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Phase 2: Alternative Drainage Facility Evaluation

1.3 Phase 2 Scope

Phase 2 of the Bosley Wash Drainage Master Plan includes the evaluation of alternatives
and the recommendation of a preferred alternative plan. Specific elements of the effort
include the development of alternatives that mitigate the flood problems identified within
the Watershed. An evaluation will be conducted that determines the effectiveness of
identified alternatives in reducing the flood hazard to properties within the basin.
Conceptual level costs and benefits will be identified. The results of these evaluations
will be used to recommend an alternative that repres.ents the consultants preferred plan.
This plan is presented in this Phase 2 Report.

1.4 Phase 3 Summary

Phase 3 of the Bosley Wash Drainage Master Plan will include the preliminary design of
the facilities selected by the County, the GJDD, CWCB, and the citizens of the Bosley
Wash Watershed. A report will be prepared that summarizes the recommendations and
presents preliminary design drawings of the selected plan. The Phase 3 Report is not
intended to present the design with a level of detail sufficient to enable construction of
the facilities.

2.0 PROBLEM IDENTIFICATION

The Phase 1 Floodplain Delineation included the development of a thorough
understanding of the nature and cause of many of the flooding problems within the
Watershed. This understanding helped us identify problem areas within the Watershed
and better understand the cause of those problems. The following sections describe the
location and character of the problems within the Watershed.

2.1 Inadequate Channel Capacity

Limited channel capacity represents one of the major problems within the Watershed.
There are several locations where the amount of water reaching a particular reach of
channel cannot be adequately conveyed by the channel in its current configuration. In
some cases, this limited capacity causes flooding in the immediate vicinity of the

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