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

DEBRIS BASIN, TEMPORARY (Urban)

A debris basin is a barrier or dam constructed across a
watercourse or gully to form a silt or sediment trap. Its
purpose is to reduce erosion from construction sites
and thereby abate pollution.

Temporary debris basins may be used where:

1. Failure of the structure would not result in loss of
life or interruption of use or service of public
utilities.

2. The storage capacity below the crest of the ungated
outlet pipe does not exceed two acre feet and the
dam is less than 19 feet high when measured from
crest to low point along centerline.

3. The drainage area does not exceed 100 acres.

4. Removal of the dam is anticipated after the con-
tributing watershed is adequately protected from
erosion. This will generally be less than three years.

5. Plans meet the requirements of the State Engineer
of Colorado as an Erosion Control Dam and shall be
filed as such.

A temporary debris basin applies to construction sites
where plans to control erosion cannot reasonably be
expected to prevent a damaging amount of sediment
from leaving the sites.

Design Criteria

Temporary debris basins must be so designed that the
combination ofthe conduit and emergency spillway will
convey the expected peak runoff. Peak runoff shall be
assumed to be equal to 3 cfs per acre. All debris basins
should incorporate an ungated outlet pipe at such eleva-
tion that full pipe flow will develop prior to operation of
the emergency spillway. The minimum pipe diameter
shall be 12 inches.

The basin sediment storage capacity shall not exceed 2
acre feet unless provision is made for a low stage drain
at the 2 acre foot level.

Basin capacity should be maintained at 50 percent (or
greater) of original volume by clean out as needed.

Principal Spillway

Capacity of pipe spillways may be obtained from Table
6. The pipe spillway may consist of a vertical riser pipe
jointed to an outlet conduit or simply a culvert type
outlet conduit with either a conventional or hooded
inlet. If a riser is used it must have an area of 1.5 times
the area of the outlet conduit. All connections shall be
watertight at expected heads.

Table 6
Capacity of Corrugated Metal Pipe Structures

Dia,
in
inches
12
15
18
24
30
36

Area
in
Sa. Ft.
.785
1.23
1.77
3.14
4.91
7.06

.116
.086
.067
.046
.034
.027

Kp

6
4.8
8.5
13.5
27.1
46.0
70.0

Discharge 1
Cubic Feet Per Second
Head on Pipe in Feet
8 10 12
5.6 6.2 6.8
9,9 11.0 12.1
15.5 17.4 19.0
31.2 34.9 38.2
53,0 60.0 65.0
81.0 91.0 100

1 Based on full pipe flow using the formula Q = A 2e h assuming
2+KpL

An "n" value of 0.025 and a length (L) of 70 feet
For L greater than 70 reduce Q values by 5 percent for each 10 feet of added pipe
For smooth steel pipe, increase Q values by 30 percent

60