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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Bosle.y _"YC!:~h pr.ainag;c!l1aster P!an

Phase 2: Alt~rnative Drainage Facility Evaluation

the flow crosses under the Government Highline Ca.nal via culverts and eventually
reaches the Hency Waste, finally rejoining Bosley \'Iash where it crosses under Hwy 6
and the UPRR. The remainder of the overflows flow west along the Government
Highline Canal and rejoin Bosley Wash at G Road (see Figure 3).

2.1.3 F % Road

Uncontrolled overflows create the most significant impact at F % Road. Undersized
culverts and low banks result in frequent overtopping of the channel in this area. Any
overflows leaving the channel flow straight downhill to the south (see Figure 4).
Overflow along the west end of F % Road never rejoins the channel. It flows south,
eventually ponding along the Hwy 6 1pd UPRR emb<>nkP1ent. }1uch of this watp.r drains
to the west through a small culvert at 34 Road. Some of the water does drain back into
the Bosley Wash Watershed, but only as a result of the deep ponding of water in this
area. Overflows further to the east along F % Road flow in a more southeasterly direction
and rejoin the main channel as the channel nears Hwy 6 and the UPRR. Once again, the
actual overland flow is relatively shallow.

2.2 Undersized Culverts

Undersized culverts are a frequent source of flooding within the Bosley Wash Watershed.
In these areas, the limited capacity of the culverts causes water to backup. This backup
often causes overflows similar to those described earlier. Unfortunately, the backups are
sometimes in areas where the topography precludes overflows. In these areas, the water
must pond until it eventually drains through the culvert. This inadvertent ponding
presents an entirely different set of problems that will be discussed in more detail in
Section 2.3.

2.2.1 G Road

The culvert conveying flows under G Road is significantly undersized. The existing 6x8'
box culvert is capable of conveying approximately 200 cubic feet per second (cfs),
substantially less than the 630 cfs that reach the crossing. The resulting backup of water
inundates a considerable area upstream of G Road. This ponded water extends along the

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