Coastal Environments: An Introduction

Coasts- an introduction.
The coast is that unique, valuable, and often threatened area where the sea meets the land. The coastline is an ever-changing boundary zone between the habitable terrestrial environment and the inhospitable marine environment. Coasts are valued in many ways as they are:

*premium economic sites for industry and marine trade

*rich and diverse habitats and ecosystems

*highly valued sites of tourism and recreation

*a natural form of coastal protection (wide, gently sloping beaches)

*sites of dense residential development

There is considerable competition for land and sea resources by various groups, often resulting in severe conflicts. Coasts form geomorphologically active landscapes, undergoing constant change.

Coastal Systems
It is important to realise that coasts are dynamic and places of constant change. The changes are the result of four independent controlling influences, and they are listed below:

*Global tectonics- can operate over a very long period of time

*Relative land-sea changes- can operate over a very long period of time

*Intervention by humans (short-term of rapid impact)- i.e. sea defences, port development, recreation, industrial or residential development.

*Natural processes of coastal erosion and deposition- accretion.

It is the latter that will be mentioned first in this blog.

Short-term natural processes
This section will focus on the short-term natural processs, and explore how waves, tides, winds and mass movement processes can change the form of coasts. This section will be broken down into a further three sub-sections.

What are the energy and sediment inputs into the coastal system?

Source of coastal sediment- The narrow zone between high and low water (the littoral zone) is a place where energy and sediment concentrate. The energy sources include wind, waves, and tidal currents. The sediments on the coast include sand, shingle and clay. Under natural conditions, there is always a balance between the energy levels and the sediment movements so that erosion taking place in one location is balanced by deposition taking place somewhere else.

Rivers bring sediment from the land to the coast. Usually fine grained silts, clays and sands. This can result in salt-marshes and deltas. Erosion of cliffs by the sea produces large amounts of material for beach building. Usually coarse sand and shingle is produced. The sea is an important source of sediments. Huge volumes of sand and clay were deposited here in the ice age. Tides and waves may bring these shorewards to build offshore bars or add to beaches.

Sources of coastal energy
There are three main energy sources at work in the coastal zone: the wind, waves and currents.

The Wind- The wind can be very effective at moving sand inland to produce sand dunes, particularly on beaches with shallow, offshore gradients and a large supply of sandy sediment. These often produce important ecosystems, such as Oxwich Bay in South Wales, and the Studland dunes of Dorset.

A picture to show dunes that have been formed at Saunton Sands, North Devon.

Waves
The power of waves depends on the wave height. A smallincrease in wave height produces a large increase in wave energy. The wave height depends on the speed of the wind, and the length of time the wind has been blowing over the sea. This depends on the distance- or fetch. In Britain, the maximum fetch is west and south-west over the Atlantic.

Tidal Currents
Incoming (flood) and outgoing (ebb) tidal current can move fine-grained sand and silts. Tidal currents are most powerful where the tide range is high and the coastline is a funnel shape.