FLOOD06100

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Design of Stable Channels with Flexible Linings
• Date: 10/1/1975
• Prepared By: Hydraulics Branch, Federal Highway Adminstration
• Floodplain - Doc Type: Educational/Technical/Reference Information

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8. Determine velocity from R and slope, So' from the
Flow Velocity vs. Hydraulic Radius Charts.

9. Allowable Q = AV.

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10. If the allowable Q is much greater than the design Q,
the channel is overdesigned. If Q is less than the
design Q, the lining is inadequate. In either case,
select another channel size and return to step 5 or
select another lining material and return to step 6.
Also, consider the feasibility of additional inlets
to reduce the flow in the channel.

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11. If a grass lining is the choice from the above
computations, and it is desired to use a temporary
lining material for channel protection during the
period of grass establishment, perform steps 6, 7,
8 and 9 using the channel bottom width. and side slopes
for the grass lined channel with the selected
temporary lining material and flow rate. The IIIOSt
stable temporary lining material is a double layer of
fiber glass tacked with asphalt; however, this lining
may retard vegetation germination and growth.

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A computation sheet, shown in Figure 3, has been developed to
facilitate the above design procedure using the charts of this
circular.

Steep Side Slope Protection

When channel side slopes are steeper than 3:1, and rock riprap
is chosen as the channel lining, the channel sides may become
Wlstable. To design rip rap for the channel sides, use the
fOllowing procedure based on charts from NCHRP Report 108 (6):

>>

1. Determine the size of rock required for the
channel bottom from the procedure outlined
previously.

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2. From Chart 30, determine the angle of repose
for the bottom rock size and shape.

3. From Chart 31, determine Kl' the ratio of
maximum side shear to maximum bottom shear for
a trapezoidal channel, based on Bid and side
slope, Z.

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