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How to Protect Coastal Shorelines


Quiz Questions

1.Sea dikes are onshore structures with the principal function of protecting low-lying areas against flooding. Sea dikes are usually built as a mound of fine materials like sand and clay with a gentle seaward slope in order to reduce the wave runup and the erodible effect of the waves. The surface of the dike is armored with grass, asphalt, stones, or concrete slabs.
True
False
2. Seawalls are onshore structures with the principal function of preventing or alleviating overtopping and flooding of the land and the structures behind due to storm surges and waves. Seawalls are built parallel to the shoreline as a reinforcement of a part of the coastal profile. Quite often seawalls are used to protect promenades, roads, and houses placed seaward of the crest edge of the natural beach profile. In these cases a seawall structure protruding from the natural beach profile must be built. Seawalls range from vertical face structures such as massive gravity concrete walls, tied walls using steel or concrete piling, and stone-filled cribwork to sloping structures with typical surfaces being reinforced concrete slabs, concrete armor units, or stone rubble.
True
False
3.Reef breakwaters are in principle designed as a rubble-mound structure with submerged crests, as shown in Figure VI-2-15. Both homogeneous and multilayer structures are used. This example shows a mound of smaller stones protected by an armor layer of larger stones.
True
False
4.According to table V12-1-1, the function of submerged break water is:
Reduction of wave height.
Reduction of longshore transport of sediment.
5.The main purpose of Beach drain is accumulation of beach material on the drained portion of beach.
True
False
6.Figure VI-2-1 Is an example of
Asphalt-armored sea dike
Seawall /revetment structure.
7.Jetties are used for stabilization of navigation channels at river mouths and tidal inlets. Jetties are shore-connected structures generally built on either one or both sides of the navigation channel perpendicular to the shore and extending into the ocean. By confining the stream or tidal flow, it is possible to reduce channel shoaling and decrease dredging requirements. Moreover, on coastlines with longshore currents and littoral drift, another function of the jetties is also to arrest the crosscurrent and direct it across the entrance in deeper water where it represents less hazard to navigation. When extended offshore of the breaker zone, jetties improve the maneuvering of ships by providing shelter against storm waves. Jetties are constructed similar to breakwaters.
True
False
8.Concrete armor units are almost always placed randomly on the slope in a layer that has a thickness of two armor units. Exceptions are Accropodes7 and Core Locs7, which are placed in a layer having thickness of one armor unit, and multi-hole cubes which are placed orderly in a regular pattern where each unit rests against
adjacent units.
True
False
9.Figure VI-2-24 shows examples of:
Different breakwater designs
Many existing types of concrete armor units.
10.Breakwaters are built to reduce wave action in an area in the lee of the structure. Wave action is reduced through a combination of reflection and dissipation of incoming wave energy. When used for harbors, breakwaters are constructed to create sufficiently calm waters for safe mooring and loading operations, handling of ships, and protection of harbor facilities. Breakwaters are also built to improve maneuvering conditions at harbor entrances and to help regulate sedimentation by directing currents and by creating areas with differing levels of wave disturbance. Protection of water intakes for power stations and protection of coastlines against tsunami waves are other applications of breakwaters.
True
False
11.How many different classifications do we have for breakwater.
One; Sloping- front structures
Two; sloping-front and vertical -front structures
12.Sloping-front structures are in most cases rubble-mound structures armored with rock or concrete armor units, with or without wavewall superstructures. Vertical-front structures are in most cases constructed of either sandfilled concrete caissons or stacked massive concrete blocks placed on a rubble stone bedding layer. In deep water, concrete caissons are often placed on a high mound of quarry rock for economical reasons. These breakwaters are called composite structures. The upper part of the concrete structure might be constructed with a sloping front to reduce the wave forces. For the same reason the front wall might be perforated with a wave chamber behind to dissipate wave energy. Smaller vertical structures might be constructed of steel sheet piling backfilled with soil, or built as a rock-filled timber cribwork or wire cages. In milder wave climates sloping reinforced concrete slabs supported by batter piles is another possibility.
True
False