Coastal Construction Manual - National Ready Mixed Concrete ...

3 IDENTIFYING HAZARDS
accretion of this ice is termed atmospheric ice. Fortunately, typical coastal residential buildings are not
considered ice-sensitive structures and are not subject to structural failures resulting from atmospheric ice.
However, designers should consider proximity of coastal residential buildings to ice-sensitive structures (e.g.,
utility towers, utility lines, and similar structures) that may fail under atmospheric ice conditions. Designers
should also be aware that ice build-up on structures, trees, and utility lines can result in a falling ice hazard
to building occupants.
3.4 Coastal Flood Effects
Coastal flooding can originate from a number of sources. Tropical cyclones, other coastal storms, and
tsunamis generate the most significant coastal flood hazards, which usually take the form of hydrostatic
forces, hydrodynamic forces, wave effects, and flood-borne debris effects. Regardless of the source of coastal
flooding, a number of flood parameters must be investigated at a coastal site to correctly characterize potential
flood hazards:
Origin of flooding
Flood frequency
Flood depth
Flood velocity
Flood direction
Flood duration
Wave effects
Erosion and scour
Sediment overwash
Flood-borne debris
CROSS REFERENCE
See Section 8.5 for
procedures used to calculate
flood loads.
If a designer can determine each of these parameters for a site, the specification of design flood conditions is
straightforward and the calculation of design flood loads will be more precise. Unfortunately, determining
some of these parameters (e.g., flood velocity, debris loads) is difficult for most sites, and design flood
conditions and loads may be less exact.
3.4.1 Hydrostatic Forces
Standing water or slowly moving water can induce horizontal hydrostatic forces against a structure, especially
when floodwater levels on different sides of the structure are not equal. Also, flooding can cause vertical
hydrostatic forces, or flotation (see Figure 3-18).
3.4.2 Hydrodynamic Forces
Hydrodynamic forces on buildings are created when coastal
floodwaters move at high velocities. These high-velocity flows are
capable of destroying solid walls and dislodging buildings with
inadequate foundations. High-velocity flows can also move large
quantities of sediment and debris that can cause additional damage.
High-velocity flows in coastal areas are usually associated with one
or more of the following:
Storm surge and wave runup flowing landward, through
breaks in sand dunes or across low-lying areas (see Figure 3-19)
CROSS REFERENCE
Predicting the speed and
direction of high-velocity
flows is difficult. Designers
should refer to the guidance
contained in Section 8.5.6
and should assume that the
flow can originate from any
direction.
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