FLOOD02558

• County: Statewide
• Community: State of Illinois
• Basin: Statewide
• Title: Ideas for Protecting Your House from Flood Damage
• Date: 6/15/1979
• Prepared By: Illinois DOT, DWR
• Floodplain - Doc Type: Educational/Technical/Reference Information

Static Lateral Pressure:

Water weighs 62.S pounds per
cubic foot. Because it is so
fluid, standing water exerts
the same pressure sideways
that it does downwards. As
the depth increases, the
pressure at the bottom
increases. The formula for
computing the pressure is:

Static load = 62.S lbs/Ft3 X (depth)

Using this formula, one can
of a wall holding back four
pounds per square foot.

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.(~ WA

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LL

see that the lateral pressur3 at the bottom
feet of water is 62.S lbs/Ft x 4 Ft = 2S0

As the formula shows, static
pressure is dependent on
height, not how big an area
the flood may cover. Since
the effects of weather have
caused the ground against
most every house to contract
away from a basement wall,
floodwaters will get an
entire basement wall wet.
Once wet, the lateral
pressure is transferred to
the wall and is computed
from the floor or base of
the wall .

1FT.

I
('FT.

.......1

. .

7fT.OI'~
~U"'l.'> 2
4~7.~ llY-l./F'T.
~ ecrrOM

Where the basement floor is 6' underground,
a flood depth of l' above ground exerts
the same pressure as 7' of flood water.

What all this discussion means is that the lateral pressures, pressures
on your house's walls during a flood, can be tremendous. Most house's
walls are not built to hold up against such lateral pressure. In fact,
when a new basement is built, the contractor normally does not back fill
until the first floor is in place to reinforce the walls to prevent
collapsing. For another comparison, the lateral pressure of water can
be 2y, times that of soil.

How much pressure can the average wall take? Here are some general rules:

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