1.1.2 Temporal variations and their influence on coastal environments

Tides:

• Tides are the rise and fall of sea level. Semi-diurnal tides have two high tides and two low tides, every 24 hours, while diurnal tides have one high tide and one low tide

• Tides created by the gravitational effect of the moon (and to a lesser extent the sun), which pulls water on Earth towards it to create high tides, with a balancing increase in water on the opposite side of the earth

• Between these two areas the sea level is lower, creating low tides

• Movements of the earth, moon and sun result in changes in the gravitational pull and changes in tides

• Twice a month the earth, moon and sun are aligned, so the gravitational pull is greatest, creating higher than average tides called spring tides

• When the sun and moon are at right angles to each other the gravitational pull is weaker, creating lower than average tides known as neap tides

• The tidal range is the difference in height between high and low water during the monthly tidal cycle. It influences the zone where coastal processes occur

Offshore and onshore currents:

• Ocean currents refer to the permanent, direct movements of water in the Earth’s oceans, which can affect coastal environments by influencing the climate.

• Onshore/offshore currents are on a more local scale, and have a greater impact on coastal processes and landforms

• Offshore and onshore currents are flows of water occurring in the coastal zone. There are three types;

  • Tidal currents- water floods the intertidal zone at high tide, moving and depositing sediment. As the tide falls (ebb tide), sediment moves in the reverse direction

  • Shore normal currents- waves align parallel to the coastline, pushing water straight up the beach. Water running directly away from the shore can form strong, fast-moving channels of water called rip currents

  • Longshore currents- waves approach the shoreline at an oblique angle, but return straight down the beach, moving sediment parallel to the shore

Constructive and destructive waves:

• Waves are created by the transfer of energy from the wind blowing over the sea surface. Stringer winds increase frictional drag and the size of waves

• Destructive waves are usually more frequent in winter, with stormier weather. This is due to the jet stream steering more Atlantic depressions over the UK during winter. Atlantic depressions occur more frequently and are more intense during winter months