FLOOD08354

• County: Boulder
• Community: Lafayette
• Stream Name: Coal Creek , Waneka Reservoir
• Basin: South Platte
• Title: Major Basinwide Planning
• Date: 12/1/1980
• Prepared For: Boulder County
• Prepared By: Camp Dresser & McKee
• Floodplain - Doc Type: Floodplain Report/Masterplan

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v. BASIS OF DESIGN

use the fioodplain wisely. For existing human occupied structures inside the

floodplain, purchase of flood insurance is encouraged to minimize the fiood

losses. This is of particular importance to those areas lying inside the

flood prone areas identified on Figure 5 and in the 100-year fioodplain of Coal

Creek (Reference 2).

The City of Lafayette, Boulder County, Phase A, Development of Alternative Plans
for Basinwide Drainageway Planning prepared by Camp Dresser and McKee Inc.,
March, 1980, developed the basic data and the potential alternatives so that
City of Lafayette, Boulder County and Urban Drainage and Flood Control District
could select the most desirable alternative. The selected alternative consists
of seven major drainageways, mostly consisting of grass lined open channels,
closed conduits and street crossings. All the proposed drainageway improvements
were designed in accordance within the City of Lafayette and surrounding Boulder
County Storm Drainage Design and Technical Criteria, also prepared by Camp
Dresser and McKee Inc. in cooperation with the project sponsors. The following
paragraphs briefly describe the design criteria used in the Phase B portion of
this study.

Open Channels

Open channels were used in the major drainageway planning wherever possible.
Grass-lined channels have a relatively low initial construction cost for a given
capacity and can also serve as open green belts for the area, The maintenance
trails along channels can also serve as hiker/biker trails. All the proposed
grass-lined channels contain a 3-foot wide by 8-inch deep trickle channel in
order to move low fiows through the major basins and prevent stagnation. A
concrete lined channel was used in one area due to the lack of available
right-of-way for a grass-lined waterway.

The grass-lined channels were design to operate at a maximum of 5-foot depth
(plus freeboard), a one-foot freeboard above the design flow water surface,
7 feet per second maximum velocity at the 100-year fiow, maximum of .7 percent

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