FLOOD06514

• County: Statewide
• Basin: Statewide
• Title: Colorado Erosion Control Manual
• Date: 11/1/1992
• Prepared For: CWCB
• Prepared By: USGS
• Floodplain - Doc Type: Floodplain Report/Masterplan

Methods For Controlling Erosion

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Dikes - Dikes are useful for bank protection where the water depth adjacent to the bank
is greater than four feet, and the stream velocity is too high for other techniques. There
are two t) pes of dikes, permeable and impermeable. Permeable dikes allow water and
sediment to flow through with reduced velocity while impermeable dikes are used to
reduce ri"er width. While both types of dikes are constructed perpendicular to the
stream ba 11<, permeable dikes uses timber piles as the main ingredient for construction
while iffi'Jermeable dikes use stone. Permeable dikes design criteria depends on
sediment load and most have horizontal bracing throughout the structure. Factors that
affect the design of the impermeable dikes are severity of expected flows, method of
constructiJn, and maintenance requirements. Regardless of the type of dike used the
design length of the structure should be at least one-third the length of the desired
protection. Since eroding banldine can be great in length, multiple dikes will be needed
to produce, the desired effecl. A typical dike is illustrated in Figure 4 - 14.

Dikes WI also be useful in a variety of rivers ranging from high or low gradient
tributaries and secondary alluvial streams. Also, permeable dikes require flows with
high sedinentloads and impermeable do not require a high concentration of sediment to
protect th: banldine. Dikes become more economical than riprap as the depth of the
water increases, but, it is safer to use a continuous form of bank protection on bank
curves gnoater than thirty degrees. Dikes produce deep and narrow stream channel but
becomes ineffective when overtoPped with high water. In 1988, permeable dikes
construction costs for a "typical" project in the midwest were $75 per linear foot of
banldine. Costs for a similar project using impermeable were $170. No maintenance
costs vary greatly due to the dynamics of the situation. Maintenance costs for permeable
dikes depend on the use of treated or untreated timber piles. Consult the appropriate
section in the state Highway Specifications for minimum requirements for timber piles.

FIGURE 4.14

Dike

Lash Brosh To
Post and Cables

3Q.60'

Deadman ~

1\\
111\ \
1111\'
1111\\
I I II \ \
V V \l

II
II
II
II
II
V

II
II
II
II
II
V

"
I,
"
"
, I
V

Rock Depth 4-6' Typical

Fence Dii<es . Fence dikes are very similar in design to hardpoints and jetties. The
difference lies in the materials used. Pence dikes consist of wood planks or wire mesh
attached 10 timber piles extending riverward of the erocling bank. Slone is often used as
a foundat lon, or is placed at the end of the structure to reduce scour. When wire mesh is .
used, it is typically backfilled with another material such as brush or hay. The impact to

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Colorado Erosion Control Manual