EM 1110-2-1100 (Part V)
31 Jul 2003
Toe failure and unraveling.
Excess groundwater pressure and piping failure through the armor layer.
Rotational sliding along the slip-circle surface
Flanking of the end sections.
(c) Armor layer stability is discussed in detail in Part VI-5-3-a; toe stability and protection in VI-5-3-d,
and filter layer design in VI-5-3-b. Shore protection by revetments can be for all levels of wave energy. For
low wave energy environments in bays and rivers, relatively inexpensive and readily available stone sizes
makes revetments a common choice for erosion protection by individual property owners. Vegetation and
marsh grasses seaward of the revetment also diminish some wave energy to protect the revetment.
(4) Combinations and other types. Protective revetments on dikes are an example of combination coastal
armoring structures. Earthen dikes, with stone revetments have been constructed to protect Texas City,
Texas, and along the Lake Erie shoreline by the USACE. Due to the nature of the earthen structure, design
and specifications should be evaluated by geotechnical engineers (see EM 1110-2-1913, "Design and
Construction of Levees"). In the Netherlands, the sea side is heavily armored to protect the dike against the
North Sea. On the land side, grazing sheep are used to continually compact the earth.
(a) As previously discussed, a storm surge barrier (see Figure V-3-1) across the opening to the sea
provides alternative means of armoring for shore protection. The most notable hurricane barrier in the United
States is located at New Bedford Harbor, Massachusetts. The tide (or flood) gate remains open for
navigation, then closes to prevent flooding of inland areas during storms.
(b) When insufficient space or earthen dike materials are available, rigid, vertical flood walls may be
constructed. Design guidance is available in EM 1110-2-2502, "Retaining and Flood Walls." Crossing the
wall requires flood gates that roll, swing, or slide to close the opening EM 1110-2-2705, "Structural Design
of Closure Structures for Local Flood Protection Projects." Special, interior drainage facilities may also be
needed including pumping stations (EM 1110-2-3102, "General Principles of Pumping Station Design and
Layout."). Grade raising, i.e., increasing ground elevation by filling with stable material is also possible. The
entire city of Galveston, Texas, was elevated about 4 m to match the seawall crest elevation. (see Figure V-3-
5). Sandy material was dredged from nearby Galveston Bay and pumped hydraulically to fill the island.
Wiegel (1991) presents a complete history of the Galveston, Texas seawall.
b. Functional design.
(1) The functional design of coastal armoring structures involves calculations of wave runup, wave
overtopping, wave transmission, and reflection. These technical factors together with economic,
environmental, political (social), and aesthetic constraints all combine to determine the crest elevation of the
structure.
(2) Wave runup and overtopping depend on many factors. Part VI-5-2 presents all the details.
Empirically determined coefficients, formulas, tables, etc. have mainly come from laboratory scale
experiments with irregular waves in large wave tanks. Independent variables include wave characteristics,
water depths, slopes, roughness, degree of permeability or impermeable, wave angle, berm or continuous
slope, freeboard, etc. Tables VI-6-18, 19, and 20 in Part VI-6 present partial safety factors for runup on rock-
armored slopes, hollowed cubes, and dolosse armor units, respectfully.
Shore Protection Projects
V-3-25
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