5.8 General Overview of Hard-Defense Options

Hard defenses. Hard-defense solutions often are interventions including gray infrastructure that affect wave intensity and sediment transport. These include artificial headlands, groins, offshore structures such as breakwaters, and seawalls and revetment rock armors. They are often made of natural stones, concrete, or a combination, and their main objectives are to absorb and disperse wave intensity, influence sediment transport, or affect both wave intensity and sediment transport. Box 5.8 provides an overview of some of the most often used hard-defense structures.

BOX 5.8

General Overview of Hard-Defense Options

Hard-defense solutions include a variety of options, some of which are placed foreshore (figure B5.8.1), and others are located on the shore (figure B5.8.2). The figures show both the intended effects of such protection solutions and their unintended, possibly disadvantageous, effects. For some examples of such solutions that were used in the Arab Republic of Egypt, see photo 5.4.

Foreshore Structures Groins. Foreshore structures such as groins (row 1 of figure B5.8.1) are structures built approximately perpendicular to the shoreline outward to locally trap transported sediments by shoreline drift. The objective is to stabilize the shoreline by decreasing sediment transport away from certain sites and encouraging buildup of beaches there; there may again be adverse effects on nearby areas. They can be built out of different materials, including wood poles, timber, or rocks.

Jetties. Built in a similar fashion, jetties (row 2 of figure B5.8.1) are typically installed for the protection of navigation channels used by ships. Their interference with natural sediment transport can also cause erosion in and along other coastal areas downdrift.

Breakwaters. Breakwaters (row 3, figure B5.8.1) can be built offshore and reduce the impact of waves on the coast to minimize coastal erosion and inundation along the coast locally to protect strategic points of the shoreline. When connected to the shore, they are also often called artificial headlands.

Temporary breakwaters or headlands can be formed of gabions or sandbags, but those will dissipate faster and are used for shortterm protection.a These structures hinder the process of coastal erosion primarily by reducing the energy with which waves arrive at the shore. Artificial headlands additionally encourage the buildup of beaches by trapping sediment brought in by waves. However, this trapping interferes with the natural flow of sediments and could cause increased erosion at other parts of the coast.

In addition, geotextile tubes are increasingly used in civil and environmental

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