Hard engineering involves the construction of

hydraulic structure A hydraulic structure is a structure submerged or partially submerged in any body of water, which disrupts the natural flow of water. They can be used to divert, disrupt or completely stop the flow. An example of a hydraulic structure would be a da ...

s to protect coasts from

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

. Such structures include

seawall A seawall (or sea wall) is a form of coastal defense constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a seawall is to protect areas of human habitation, conservation ...

gabion A gabion (from Italian ''gabbione'' meaning "big cage"; from Italian ''gabbia'' and Latin ''cavea'' meaning "cage") is a cage, cylinder or box filled with rocks, concrete, or sometimes sand and soil for use in civil engineering, road building, ...

breakwaters A breakwater is a permanent structure constructed at a coastal area to protect against tides, currents, waves, and storm surges. Part of a coastal management system, breakwaters are installed to minimize erosion, and to protect anchorages, h ...

groyne A groyne (in the U.S. groin) is a rigid hydraulic structure built perpendicularly from an ocean shore (in coastal engineering) or a river bank, interrupting water flow and limiting the movement of sediment. It is usually made out of wood, concre ...

s and

tetrapods Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids (reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct therapsids ...

Effects

Hard engineering can cause unintended environmental consequences, such as new

and altered

sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the ...

patterns, that are detrimental to the immediate human and natural environment or along down-coast locations and

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

Seawalls A seawall (or sea wall) is a form of coastal defense constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a seawall is to protect areas of human habitation, conservation ...

and bulkheads may have multiple negative effects on nearshore ecosystems due to the way they reflect wave energy instead of dissipating it. Energy from reflected waves can cause a scouring effect on substrate below the structure, resulting in loss or displacement of sediment. Over time, this effect may lead to a decrease in the size of intertidal and nearshore habitats. This effect is also known as coastal squeeze. In addition, bulkheads and seawalls offer no filtering for

surface runoff Surface runoff (also known as overland flow) is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when th ...

, this means that anthropogenic pollutants and chemicals in armored areas may enter coastal waters relatively quickly. Hard engineering, also called shoreline armoring, comes with other ecological effects on top of habitat loss and increased surface runoff. Structures that are built between land and sea are usually made of material not native to shoreline ecosystems. For instance, most sea walls and interlocking coastal defense structures are made of concrete, which may lend itself as habitat for invasive species rather than native ones. These structures also impede shoreline access, blocking some or all species from accessing refuge on dry land. In these armored areas, we also see that nutrient exchange between tidal and riparian ecosystems is threatened or cut off entirely. These issues arise from hard engineered sea shores, and lead many to believe that living shoreline techniques are far more beneficial ecologically and in terms of long-term erosion control.

Examples

Examples of hard engineering include: *

Groyne A groyne (in the U.S. groin) is a rigid hydraulic structure built perpendicularly from an ocean shore (in coastal engineering) or a river bank, interrupting water flow and limiting the movement of sediment. It is usually made out of wood, concre ...

s – Low walls constructed at right angles to retain sediments that might otherwise be removed due to

longshore drift Longshore drift from longshore current is a geological process that consists of the transportation of sediments (clay, silt, pebbles, sand, shingle) along a coast parallel to the shoreline, which is dependent on the angle incoming wave direction ...

. These structures absorb or reduce the

energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...

of the waves and cause materials to be deposited on the updrift side of the groyne facing the longshore drift. *

Seawall A seawall (or sea wall) is a form of coastal defense constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a seawall is to protect areas of human habitation, conservation ...

s – Seawalls are constructed to protect coastlines against wave attack by absorbing wave energy. Most seawalls are made out of

concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...

stone In geology, rock (or stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemical compound, chemical composition, and the way in which it is formed. Rocks ...

and are built parallel to the coast. They have been constructed in thousands of locations throughout the world. * Rip-rap/rock armour – Boulders piled up against the coast that absorb the energy of the waves *

Gabion A gabion (from Italian ''gabbione'' meaning "big cage"; from Italian ''gabbia'' and Latin ''cavea'' meaning "cage") is a cage, cylinder or box filled with rocks, concrete, or sometimes sand and soil for use in civil engineering, road building, ...

s – wire cages filled with rocks to absorb wave energy

References

Water and the environment {{hydrology-stub