FLOOD04566

• County: Boulder
• Community: Boulder
• Stream Name: Gregory, Bear Can, Bluebell Can Creeks, Viele Chan
• Basin: South Platte
• Title: Major Drainageway Planning Volume 1, Part C
• Date: 9/1/1970
• Prepared For: Boulder County
• Prepared By: CWCB
• Floodplain - Doc Type: Floodplain Report/Masterplan

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38

c, The flood plain limits must be defined

d. Filling of flood plain fringes should not be allowed in order
to maintain channel storage capability,

e. Hydraulic roughness should be representative of reasonably
maintained channel conditions,

f Drops or check dams should be used to control water surface
profile slope to control erosion after urbanization,

g, Perform backwater curve computations based upon existing
conditions with assumption that flood plain limits wi Ii be
revised as bridges are replaced or new roadways are constructed,

3

Riprapped or Other Lined Channels,
will be used with discretion, and
ment for minimum reaches

Higher Velocity artificial channels
only then to accommodate existing develop"

a. Riprap size, design velocity and "n" valves to be based upon figures
19, 20, and 21 of the Bureau of Public Road publication, Oesiqn of
Roadside Drainaqe Ditches and DRCOG criteria.

b. Side Slopes from 3:1 to 2:1 may be riprapped but steeper slopes must
be solidly lined with an anchored wall. The preferable section for
steeper side slopes is 0.5:1 with a retaining wall structure imbedded
with natural stone. Care must be taken for freeze thaw, ground water
and expansive soil effects.

c, The bottom of channels must generally be lined when either the velocity
exceeds 8 fps or the Froude number exceeds 0.8,

d. Use trickle channels for low flows with capacities of about one per
cent of design flow, but not to exceed 20 cfs. Riprap, concrete or
other protection to prevent eros,ion is needed,

4,

Bridqes. About one foot of clearance should be maintained between the
design water surface and the low member of a bridge.

5.

Culverts, Culverts will be used in lieu of bridges where feasible.
water effect of culverts to be consistent with channel requirements
adjacent topography, Energy dissipators must be used downstream of
verts wherever flow is supercrltical from channel standpoint,

Back-
and
cul-

a. The use of armor plating on culvert floors must be considered when
the potential for wear by moving rocks and high velocities exists.

6.

Conduits, Conduits are designed based upon the criteria included in the
storm sewers and the Major Drainage parts of the DRCOG Manual.

a. The maximum allowable velocity for a non-armored concrete conduit
shall be about 25 fps.