FLOOD09931

• County: Statewide
• Community: Urbanizing Areas of Colorado
• Basin: Statewide
• Title: A Guide for Erosion & Sediment Control in Urbanizing Areas of Colorado
• Date: 1/1/1973
• Prepared For: State of Colorado
• Prepared By: USDA Soil Conservation Service
• Floodplain - Doc Type: Educational/Technical/Reference Information

DIVERSIONS (Urban)

A diversion is a channel with a supporting ridge on the
lower side constructed across the slope. There are two
classifications of diversions:

(Temporary)

Diversions installed as an interior measure to facilitate
some phase of construction. They usually have a life
expectancy of I year or less.

(Permanent)

Diversions installed as an integral part of an overall
water disposal system and to remain for protection of
property.

Diversions are used to reduce slope lengths, break up
concentration of runoff and move water to stable out-
lets at a nonerosive velocity. They may serve such
purposes as diverting water from (I) lower lying areas,
(2) cut or fill slopes or steeply sloping land, (3) construc-
tion sites, (4) buildings and residences, and (5) active
gullies or other erodible areas.

Diversions must have stable outlets. The site, slopes,
and soils must be such that the diversion can be con-
structed and maintained throughout its planned life.
Construction of diversions and outlets must be in com-
pliance with state drainage and water laws.

Diversion Terrace

Planning

The location of a diversion shall be determined by con-
sidering outlet conditions, topography, land use,
development layout, soil type, and length of slope.
A void locations in or immediately below unstable or
highly erosive soils unless special treatment or stabili-
zation measures are previously applied.

Peak runoff values used in determining capacity re-
quirements should be determined as outlined in "Pro-
cedures for Determining Peak Flows in Colorado," or
by other accepted methods. The minimum design
24-hour storm frequencies and freeboard shall comply
with Table 4:

Grade

Channel grade for diversions may be uniform or vari-
able. The allowable velocity for the soil type and veg-
etative cover determines maximum grade. Level diver-
sions with blocked ends may be used provided pipes of
sufficient size and spacing are placed in the embank-
ment to drain the channel following cessation of runoff.

,

Table 4
Diversion
Type

Typical Areas of
Protection

Design Freeboard
Frequency Required

Temporary Construction roads;
land areas. ele.

2 yrs. 0.0

"

Building sites

5 yrs.

0.0

Permanent Land areas, play-
fields, recreation
areas, etc.

25 yrs.

0.3 ft.

Homes, schools, in- 50 yrs.
dustrial bldg., etc.

0.5 ft.

In all cases, the design storm frequency should be cho-
sen to provide protection which is compatible with the
hazard of damage that would occur if the diversion
should overtop.

Permissible design velocities should be determined by
use of Tables 5 and 6.

Table 5:

Selection of Vegetal Retardance

Average Length of
veg.. inches

Retardance

Good Stand

Fair Stand

ll-24
6-10
2-6

B
C
D

C
D
D

Table 6:

Permissible Velocities

Soil Texture

Permissible Velocity
Ft./Sec.
Bare Channel Ve~etation
Channel Retardance Poor Fair Good

Sand, silt,
Sandy loam, and
Silty loam

1.5

B 3.0 4.0
C 1.5 2.5 3.5
D 2.0 3.0
B 4.0 5.0
C 2.5 3.5 4.5
D 3.0 4.0
B 5.0 6.0
C 3.0 4.5 5.5
D 4.0 5.0

Silty clay loam
Sandy clay loam 2.0

Clay

2.5

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