FLOOD00281

• County: Larimer
• Community: Greeley
• Title: Design Criteria and Construction Specifications volume 2 of 5 Storm Drainage Criteria
• Date: 10/1/1997
• Prepared For: Greeley
• Prepared By: Department of Public Works
• Floodplain - Doc Type: Educational/Technical/Reference Information

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7.

a. Trickle Channel - The base flow shall be carried in a
trickle channel except for sandy soils. The minimum
capacity shall be 2.0 percent to 4.0 percent of the 100-
year flow but not less than 1 cfs. Trickle channels
shall be constructed of concrete or other approved
materials to minimize erosion, to facilitate maintenance,
and to aesthetically blend with the adjacent vegetation
and soils. Recommended trickle channel sections are
presented in Figure 5-5. The minimum trickle channel
width shall be three feet.

An alternative configuration for a trickle channel may
consist of a subsurface storm drain pipe. If used, this
alternative would consist of a minimum 24" diameter pipe,
provided with access manholes, and sloped to maintain a
minimum pipe flow velocity of 3 feet per second at one-
half of full pipe depth.

b.

Main Channel Representative
limitations for these channels, are
5-3, and 5.4. Figure 5.4
configurations for sandy soils.

main channels, and
shown in Figures 5-2,
indicates channel

c. Bottom width The m~n~mum bottom width shall be
consistent with the maximum depth and velocity criteria.
The minimum width shall be four feet or the trickle
channel width, where required.

d. Right-Of-Way Width - The minimum ROW width shall include
freeboard and a 12-foot wide maintenance access. In some
situations, the city may require a 12' maintenance access
on both sides of the channel.

e. Flow Depth - The maximum design depth of flow (outside
the trickle channel area and main channel area for sandy
soils) for the 100-year flood shall be limited to 5.0
feet in grass lined channels.

f. Maintenance/Access Road - continuous maintenance access
shall be provided for all major drainageways at a minimum
width of 12 feet. The City may require six inches of
Class 2 road base or a concrete slab.

g. Side Slopes - Side slopes shall be 4 (horizontal) to 1
(vertical) or flatter. Slopes as steep as 3H:1V may be
used in existing developed areas where ROW availability
is restricted, provided prior written approval is
obtained from the city.

Grass Lining (Major Drainageway)

The grass lining for channels shall be in accordance with the
USDCM, section 2.3.2, "Major Drainage - Grass lined Channels -
Grass."

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