FLOOD08470

• County: Summit
• Community: Breckenridge
• Stream Name: Sawmill Gulch
• Basin: Colorado Mainstem
• Title: Draft Tyra Tract D and Sawmill Gulch Floodplain Report
• Date: 3/19/1998
• Prepared For: Breckenridge
• Prepared By: Wright Water Engineers, Inc.
• Floodplain - Doc Type: Floodplain Report/Masterplan

FLOODPLAIN REPORT - Tyra Tract D and Sawmill Gulch, Breckenridge, Colorado
(DIIAlF'n

Proposed Conditions Model- Tract D Reach

Drawings I through 4 are permitting/design drawings for the major drainage facilities related to

Tyra Tract D. Drawing I presents the floodplain of Sawmill Gulch across the Tract D site in the

existing (pre-project) condition. Drawings 2, 3 and 4 present the facilities proposed for Tract D.

Essentially, there are no changes to the main channel floodplain, In the proposed condition, the

main channel of Sawmill Gulch, as well as its wetland setback, is respected and little or no

construction is proposed. Simply, the proposed facilities that affect flows of Sawmill Gulch are

merely collection points for the already identified out-of-bank flows that occur in the existing

condition. These out-of-bank flows will be collected above and re-directed around the proposed

building through a combination of concrete retaining walls and a 48-inch diameter culvert with

an outlet structure. A lower collection system will capture the flooding that is anticipated to

occur at Four O'Clock Road, and will transmit that water via a 30-inch diameter pipe to a

location consistent with the historic flooding on Four O'Clock Road near the project eastern

boundary. At that point, it will be joined by the flows from the 48-inch pipe which is part of the

upper collection system. Flood flows are released essentially at the same place and at the same

rate as in pre-project conditions. These collection systems are discussed in more detail in the

next major section, entitled "Hydraulic Structure Analyses," Again, it is not the intent nor the

design for these facilities to significantly alter the existing floodplain of Sawmill Gulch or the

out-of-bank flooding except to route it around the proposed building. The approach was

requested/confirmed by FEMA and Town representatives.

Proposed Conditions Model-UPPer Sawmill Gulch Reach

The proposed conditions floodplain for Upper Sawmill Gulch, that portion from Four O'Clock
Road to the Town boundary, does not differ from the existing condition. There are no proposed
construction activities upstream of Tyra Tract D, and on Tract D, as discussed in the prior
section, there are no construction activities proposed to alter the floodplain of Sawmill Gulch,
Thus, Plate I presents both existing and proposed floodplains for upper Sawmill Gulch.

971-055.010

Wright Water Engineers, Inc.

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