Coastal Engineering is the branch of civil engineering concerned with the planning, design, construction and maintenance of works in the coastal zone. Coastal engineering usually involves either 1) the transport and stabilisation of sand and other coastal sediments or 2) the construction of structures.
Measures in the first category are called ‘soft’ measures since they make use of natural (soft) coastal material. Examples are beach nourishments, maintenance dredging and land reclamation.
The second category of structures or ‘hard’ measures can be divided into various functional groups:
- Seawalls and revetments are built parallel or nearly parallel to the shoreline at the land-sea interface with the objective of preventing further shoreline recession. Seawalls are usually massive and rigid, while a revetment is an armouring of the beach face with rock armour or artificial units. Although often used, the efficacy of seawalls and revetments is debatable as we will discuss later on;
- Groynes are built perpendicular to the shore and usually extend out through the surf zone under normal wave and water level conditions. They help widen and protect a beach by trapping sand from the alongshore transport system (see Ch. 8) or by retaining artificially placed sand;
- Jettiesarestructuresbuiltattheentrancetoariverortidalbasintostabilisethe entrance as well as to protect vessels navigating the entrance channel;
- Breakwatersprimarilyprotectashorelineorharbouranchorageareafromwave attack. Breakwaters may be located completely offshore and oriented parallel to the shore (detached breakwaters), or they may be oblique and connected to the shore. Traditionally, detached breakwaters have been designed as emerged structures, but submerged breakwaters have now also become a popular option. The latter are not easily noticeable because of their low crests;
- Other structures such as submerged pipelines.
The purposes of these (‘soft’ and ‘hard’) works are diverse:
- Control of shoreline erosion;
- Defence against flooding caused by storms, tides;
- Development of coastal functions, for instance coastal recreation;
- Development of navigation channels and harbours.
Coastal engineering works are carried out in a highly dynamic and energetic environ- ment. The various sources of coastal energy are:
- Marine forces (waves, tides, currents and other oceanographic phenomena);
- Terrestrial forces (river outflow);
- Atmospheric forces (coastal winds and climate).
These forces not only directly impact the planned ‘soft’ or ‘hard’ measures, but also permanently change the physical shape and structure of a coastal system. This shape of the coast is called morphology. Coastal morphology for a sandy stretch of coast thus is the topography of the sandy dunes and beach and the underwater topography of the seabed. When changes occur in the external forcing, the coastal morphology
will change accordingly. Changes in the forcing can have a natural cause or can be human-induced. Examples of changes in the forcing conditions are:
- High waves and piling up of water against the coast (surge) due to the occurrence of a storm;
- Long-term sea-level rise;
- Changes in the wave impact on the adjacent coast due to the construction of a harbour;
- The deprivation of a coastal system of sediment supply due to the construction of a dam in a river.
Although coastal changes take place on a variety of timescales, coastal engineers and managers are mostly interested in timescales ranging from 1 year to (a few) hundred years and in large impact events like storms causing dune erosion and flooding