coasts

SYSTEM - a model used particularly in physical geography which describes a set of interrelated parts that work together 

CLOSED SYSTEM - a type of system where there is a transfer of energy between the system and the environment, but not matter. 

OPEN SYSTEM - when systems receive inputs and transfer outputs of ​energy or matter ​with other systems

CASCADING SYSTEM  - a system which describes how these systems can interlock, where the output of one forms the input of another 

ISOLATED SYSTEM - a system which has no interactions with anything outside of the system boundary. There is no input or output of matter. 

DYNAMIC EQUILIBRIUM - the term used for when there is a balance between the inputs and outputs 

THRESHOLD -  a critical tipping point in a system 

Most systems tend toward a state of equilibrium where system inputs are balanced by system outputs.

INPUTS: 

Energy from 

• waves 

• winds

• tides

• Sea currents 

Sediments 

Geology of coastline 

Sea level change 

OUTPUTS: 

Dissipation of wave energy 

Accumulation of sediment above the tidal limit 

The state of natural systems oscillates around a mean condition – a state known as dynamic equilibrium. This is achieved via positive and negative feedback.

Positive feedback - when there is a change that amplifies the effect 

E.g Damage to vegetation on a sand dune by trampling causes erosion of sand, resulting in further loss of vegetation, more erosion

Negative feedback creates a change that reverses the effect and restores a system to balance (Negative feedback is more common on coastlines)

THRESHOLD - A critical ‘tipping point’ in a system. 

For example, if a cliff receives a substantial input of water, such as from a period of intense rainfall, the additional weight of that water can ‘tip’ the slope past its equilibrium point (stability threshold). Mass movement then occurs

Coastal landscapes and landforms

The processes within a coastal system form the landforms and landscapes found there

LANDFORM – a natural feature of the Earth’s surface. 

E.g headlands, cliffs, arches, stacks, beaches spits etc 

LANDSCAPE – the visible features of an area of land, its landforms and how they integrate with natural or man-made features.

Littoral Zone 

The coastline consists of a series of different zones where specific conditions prevail that depend on a number of factors. The diagram shows how these zones relate to each other

BACKSHORE 

- the area between the high water mark (HWM) and the landward limit of marine activity. 

- Changes normally take place here only during storm activity. 

FORESHORE 

- the area lying between the HWM and the low water mark (LWM) 

- It is the most important zone for marine processes in times that are not influenced by storm activity.

INSHORE 

- is the area between the LWM and the point where waves cease to have any influence on the land beneath them.

OFFSHORE 

- is the area beyond the point where waves cease to impact upon the seabed and in which activity is limited to deposition of sediments.

NEARSHORE 

- is the area extending seaward from the HWM to the area where waves begin to break. It includes the following:

 – Swash zone: the area where a turbulent layer of water washes up the beach following the breaking of a wave. 

– Surf zone: the area between the point where waves break, forming a foamy, bubbly surface, and where the waves then move up the beach as swash in the swash zone. 

– Breaker zone: the area where waves approaching the coastline begin to break, usually where the water depth is 5 to 10 m.

3.1.3.2 Systems and processes

Sources of energy in coastal environments: winds, waves (constructive and destructive), currents and tides. Low energy and high energy coasts.

Sediment sources, cells and budgets.

Coastal sediment comes from a variety of sources, including:

● streams or rivers flowing into the sea

● estuaries

● cliff erosion

● offshore sand banks

● material from a biological origin – including shells,

coral fragments and skeletons of marine organisms.

SEDIMENT CELL -  A stretch of coastline, usually bordered by two prominent headlands, where the movement of sediment is more or less contained.

SEDIMENT BUDGET -  Material in a sediment cell can be considered in the form of a sediment budget with losses and gains.

Losses from the system involve deposition in sediment sinks, whereas gains tend to involve coastal erosion, or sediment brought into the system by rivers or from offshore sources

Geomorphological processes: weathering, mass movement, erosion, transportation and deposition.

Distinctively coastal processes: marine: erosion – hydraulic action, wave quarrying, corrasion/abrasion, cavitation, solution, attrition; transportation: traction, suspension (longshore/littoral drift) and deposition; sub-aerial weathering, mass movement and runoff.