FLOOD05148

• County: Statewide
• Community: State of Colorado
• Basin: Statewide
• Title: Urban Storm Drainage Criteria Manual
• Date: 5/1/1984
• Prepared By: UDFCD
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

DRAINAGE CRITERIA MANUAL

RUNOFF

contains the recommended limits for calculating the translation velocity .
of a hydrograph. The flow used in calculating the translation velocity
is the peak flow of the hydrograph. The peak flow is used in conjunction
with the drainageway shape, slope and roughness to calculate the normal
depth velocity (i.e. translation velocity).

Tab 1 e 4 - 2

Recommended Limits For Calculating
Direct Translation Velocity

*Maximum *Maximum
Type of Channel Velocity Froude No.
Natural Waterway 8.0 fps 0.95
Man Made:
Grass Lined 6.0 fps 0.8 **
Riprap Lined 8.0 fps 0.8 **
Concrete Lined 12.0 fps No Limit

* Use whichever results in lower velocity.
** Applies only to channels built using USDCM velocity limitations,
otherwise use F 0.95

.

4.13.2 Example - Direct Translation Channel Routing
Given: A sample watershed shown in Figure 4-7
Channel reach A-B is a 5500 feet long, trapezoidal, grass lined
channel having a 5 foot bottom, 4:1 side slopes, 0.006 ft/ft
longitudinal slope and Manning roughness n = .040.
Channel reach B-C is a 3000 feet long, natural waterway, that can be
approximately described as trapezoidal having a 20 foot bottom, 3:1
side slopes, 0.008 ft/ft longitudinal slope and Mannings roughness n
= 0.045.
Table 4-3 giving the design storm hydrographs for subbasins 1, 2,
and 3 (at design points A and B). It is assumed that the storm
hydrograph for the sub-basin tributary to design point C is very
small and will not affect final results.
Required: Composite storm hydrographs at design points Band C calculated
using direct translation method.

Solution:
Step 1. Set up Table 4-4.

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5-1-84