FLOOD04542

• County: Statewide
• Basin: Statewide
• Title: Engineering and Design Design and Construction of Levees
• Date: 4/16/1979
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

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BERM

EM 1110-2-1913

31 Mar 78

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r--..L...J SUPAGE CONCl:NTRATION

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INCORRtCT

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CORRtCT

Figure 5-1. Example of incorrect and correct berm length according
to existing foundation conditions

thickness necessary to provide an ,adequate factor of safety against
uplift .

(2) Semipervious berms. Semipervious material used in construct-
ing this type of berm should have an in-place permeability equal to or
greater than that of the top stratum. In this type or berm, some seepage
will pass through the berm and emerge on its surface. However, since
the presence of this berm creates additional resistance to flow, subsur-
face pressures at the levee toe will be increased.

(3) Sand berms. While a sand berm will offer less resistance to
flow than a semipervious berm, it may also cause an increase in substra-
tum pressures at the levee toe if it does not have the capacity to con-
duct seepage flow landward without excessive internal head losses.
Material used in a sand berm should be as pervious as possible, with a
minimum permeability of 100 x 10-4 cm per sec. Sand berms require less
material and occupy less space than impervious or semipervious berms
providing the same degree of protection.

(4) Free-draining berms. A free-draining berm is one composed
of random fill overlying horizontal sand arid gravel drainage layers
(with a terminal perforated collector pipe system), designed by the same
methods used for drainage layers in dams. Although the free-draining

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