FLOOD03449

• County: Statewide
• Community: State of Colorado
• Stream Name: All
• Basin: Statewide
• Title: Colorado Flood Proofing Manual
• Date: 10/1/1983
• Prepared For: State of Colorado
• Prepared By: CWCB
• Floodplain - Doc Type: Educational/Technical/Reference Information

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IX. INTERNAL flOODING

9.1 Introduction

As floodwater builds up on the outside of a structuro. it creates a pressure which acts
inward against the structure. If a structure has walls. slab:" or internal bracing that lack the
strength to resist this load, a structural failure can ocdn. A method that is sometimes Llsed to
prevent this kind of damage is called internal flooding;. VVdter i~ either intentiollally let in or
pumped into the structure. As Figure 9.1 shows, th(' water inside creates hydrostatic pressure
directed outwardly to balance the pressure acting irl\-v~\r(:ily.

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FORCE OF WATER

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GROUND LEVEL

.... FORCE OF
SATURATED
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UPLIFT (BUOYANCY) F~)RCE

Figure 9.1. Balanced forces by intern,,1 flooding. (Reference 12)

9.2 Implementation ConsideratiotrS

In addition to pumping, there a~e t'l-\lO other common: nlf,thods to get the water insicle. One
simply involves letting the water come in through win~ows and door openings. The windows
may be opened or designed to fail when a certain heaid of water exists. A potential problem
that can arise when floodwatE"s are let in is contaminJlion of the flooded area with bacteria
and alkali or acidic sediment. Another method u',ps a floor blow-out plug (see Figure 9.2).
This plug should be at least one foot square, and the section should be one piece cut all the
way through the slab. When replacing the plug, the joi!nt can be sealed with tar or asphalt
(me-inch deep into the crack. The soil around the bas~mellt walls and under the floor slab
should be of a permeable nature to allow adequate inflow The plug will the he pushed in
by the outside water pressure, and slab failure wili he :averted.

This form of wet flood proofing, internal flooding, rcqLji"" that al; parts of the structure
below the base flood level be constructed and fittpd \~'ith watE~r-resistant materials and
finishes. Surfaces that will contact water should be 1I0~PO-ou'; to facilitate cleaning. Cleanup
will also be easier if clean waler i~ pumped into the s~an~ rat.her than using floodwater.