Question

Coastlines are not static and undergo long term and gradual changes. What are the factors and processes that affect coastal landforms?

Answer 1

Approach:

• Straight forward question, Write the factors and processes, both natural and anthropogenic that affect coastline development.

Answer:
Coastline changes are induced by erosion and accretion are natural processes that take place over a range of time scales.

Coastlines comprise the natural boundary zone between the land and the ocean. Their natural features depend on the type of rocks exposed along the coastline, the action of natural processes and the work of vegetation and animals. The intensity of natural processes formed their origin — either as erosional or depositional features. The geological composition of a coastal region determines the stability of the soil, as well as the degree of rocky materials and their breakdown and removal.

Wind, wave and tidal current action; beach dynamics within a sediment/littoral cell; and human activities along the coast, within river catchments and watersheds and offshore, affect coastal landforms both at spatial and temporal scales.

Natural Factors and Processes:

Factors:

• Coastal geomorphology: Coastline type and sensitivity to coastal processes.
• Wind: The main force in wave generation
• Waves: They are the most important forces for sediment erosion and transport to the coastal zone. They introduce energy to the coast and also a series of currents that move sediment along the shore (longshore drift) and normal to the shore (cross-shore transport).
• It is important to understand the movement of waveforms as well as water particles and their interaction with seabed material; also how the waves determine whether the coasts are erosive or accretional.
• Tides: They are influential in beach morphodynamics. They modulate wave action, controlling energy arriving on the coast and drive groundwater fluctuation and tidal currents.
• Vegetation: Important for improving slope stability, consolidating sediments and providing some shoreline protection.

The various processes may occur in response to smaller-scale (short-term) events, such as storms, regular wave action, tides and winds, or in response to large-scale (long-term) events such as glaciation or orogenic cycles that may significantly alter sea levels (rise/fall) and tectonic activities that cause coastal land subsidence or emergence.

Hence, most coastlines are naturally dynamic, and cycles of erosion are often an important feature of their ecological character. Wind, waves and currents are natural forces that easily move the unconsolidated sand and soils in the coastal area, resulting in rapid changes in the position of the shoreline.

Anthropogenic Factors:

• Activities along the coast: Building houses via land reclamation or within sand dune areas and port/harbour development has a long-term impact on shoreline change; structures such as groynes and jetties typically cause erosion down-drift of the structure within a short period of time (between five and ten years). Removal of dune vegetation and mangroves will expose low energy shorelines to increased energy and reduced sediment stability, causing erosion within five to ten years
• Activities within river catchments/watersheds: Dam construction and river diversion cause reduction of sediment supply to the coast that contributes to coastal erosion. The effects of dams and river diversion in terms of coastal erosion are not straightforward, but there are mid-to-long-term impacts (20 to 100 years) with spatial scales approximately from one to 100 kilometres.
• Onshore and offshore activities: Sand and coral mining and dredging may affect coastal processes in various ways such as contributing to sediment deficit in the coastal system and modifying water depth that leads to altered wave refraction and longshore drift. The impact of these activities will be obvious within a short period of time (one to ten years).
• Climate change is also changing dynamics various other factors like waves, tides, winds, vegetation etc which in turn affect the coastlines.

Human activities along with the combination of natural forces often exacerbate coastal erosion in many places and jeopardize opportunities for coasts to fulfil their socio-economic and ecological roles in the long term at a reasonable societal cost.

Development within coastal areas has increased erosion problems. The erosion problem becomes worse whenever the countermeasures i.e. hard or soft structural options) applied are inappropriate, improperly designed, built, or maintained and if the effects on adjacent shores are not carefully evaluated.

Often erosion is addressed locally at specific places or at regional or jurisdictional boundaries instead of at system boundaries that reflect natural processes, which even more aggravate the problem.