Coastal engineering is a specialized branch of the engineering profession which includes the many physical science and engineering disciplines having application in the coastal area. Coastal engineering addresses both the natural and man-induced changes in the coastal zone, the structural and non-structural protection against these changes, and the desirable and adverse impacts of possible solutions to problem areas on the coast. The coastal engineer's work can be divided into three phases: understanding the nearshore physical system and the shoreline's response to it; designing coastal works to meet project objectives within the bounds of acceptable coastal impact; and overseeing the construction of coastal works and monitoring their performance to ensure that projects function as planned (USACE 2002).
The boundary between the land and water is commonly called the coastline or shoreline. The strip of land of indefinite width that extends inland to the first major change in terrain is commonly referred to as the coast or coastal zone. The coastal zone may be several miles wide. Highways that are located near coastlines and shorelines of oceans, tidal basins, bays, estuaries, and the lower reaches of many major river systems present challenging design conditions for roadway, structural, and hydraulic engineers.
The forces in coastal zones are more diverse than in typical riverine conditions and the data requirements are more extensive. There are several distinct types of hydraulic problems that may be encountered:
- Wave surge and tidal action along a coastline
- Seasonal shifts of the shore
- Along shore and offshore transport of beach sands
Floods resulting from upland runoff in combination with tides and waves. These problems are common to the Atlantic, Pacific, and Gulf coasts. Many coastlines are significantly affected by winter storms that bring large waves and storm surges. Generally the shift is a recession, increasing the exposure of beach locations to the hazard of damage by wave action. Consequently, stabilization of the shoreline is one of the most important considerations when highway facilities are located in the coastal zone. The design of foundations and protective works must be predicted on knowledge of local soils and geology. It is also necessary to determine the dominant geomorphic processes of the shore line. This type of information may be obtained from borings, soil surveys, analysis of aerial photographs, and field reconnaissance. Because shorelines may have significant temporal variability, it is necessary to obtain sufficient historical data to identify either this variability or long-term trends. The hydraulic engineer needs to recognize that these changes may be seasonal, annual, or even longer at some locations.
Pacific Coastlines
The coastline of the states bordering on the Pacific are periodically faced with El Niño. The El Niño is the common name for what most scientists refer to as the ENSO (El Niño - Southern Oscillation) phenomenon related to the interactions between the ocean and the atmospheric circulation patterns with an inter-decadal scale variability. Typically, the storms affecting the west coast of the United States are generated in the North Pacific and the waves travel southerly. El Niño events cause waves to travel in a northerly direction along the coast. The waves associated with the El Niño are frequently as large or larger than the storm waves from the North Pacific. Usually, the northeastern seaboard of the United States can credit El Niño with milder-than-normal winters and relatively benign hurricane seasons.
Tsunamis are another coastal hazard for Pacific coastlines. A tsunami is a wave, or series of waves, generated in a body of water by an impulsive disturbance that displaces the water column in a vertical or horizontal direction. Earthquakes, landslides, volcanic eruptions, explosions and even the impact of cosmic bodies, such as meteorites, can generate tsunamis. Tsunamis can savagely attack coastlines, causing devastating property damage and loss of life. As a tsunami approaches shore, it begins to slow and grow in height. As the tsunami reaches the shoreline, part of the wave energy is reflected offshore, while the shoreward-propagating wave energy is dissipated through bottom friction and breaking or turbulence. Tsunamis have a large amount of energy and very long wavelengths. As it approaches, the shoreline the wavelength becomes shorter causing a very large increase in wave height. This large wave height has great
potential for erosion and destruction. Frequently, this results in stripping beach material and depositing it landward as well as undermining trees and destroying large structures. Tsunamis have had a maximum vertical runup of as much as 100 feet.
Dynamic Beach Processes
The beach and near-shore zone of a coast is the region where the forces of the sea react against the land. The physical system within this region is composed primarily of the motion of the sea, which supplies energy to the system, and the shore, which absorbs this energy. Because the shoreline is the intersection of the air, land and water, the physical interactions that occur in this region are unique, very complex, and difficult to fully understand. While there have been significant advances in understanding beach processes in recent years, the ability to predict changes is still limited.
On coasts where the shoreline is unconsolidated sediment such as a clay, sand or silt, the energy from the waves, wind and tide can cause rapid change in the shape and dimensions of the shoreline. Waves are the most significant factor to cause shoreline change. As waves move from offshore to the beach they will often break, reform and break again. The process of breaking results in a portion of the wave energy being dissipated. Additional energy is dissipated on the beach with the resultant transport of the beach sediment.
