Wave Dominated Coasts Objective: to examine some of the processes and characteristics active on a wave-dominated coast

Weathering & Erosion What is? Weathering: Breakdown of rock (Geology) to form sediment in situ Weathering is a set of physical, chemical and biological processes that alter the physical and chemical state of rocks and soil at or near the earth's surface. Rock and soil is altered physically by disintegrating and chemically by decomposing. Nearly all weathering involves water, mostly directly: frost shattering, wetting and drying, salt weathering, and all chemical weathering is in solution. That is, weathering is climatically driven and thus the term weathering. Because weather and climate occur at the earth's surface, the intensity of weathering decreases with depth and most of it occur within less than a metre of the surface of soil and rock. Erosion:Transport of weathered material from one location to another...The wearing away of land or the removal of beach and/or dune sediments by wave action, tidal currents, wave currents, drainage, or wind. Erosion includes, but is not limited to, horizontal recession and scour and can be induced or aggravated by human activities.

Wave Dominated Coasts Coasts are exposed to the elements Open to the sea Little shelter from ‘waves’ Waves ‘erode’ the coastline Waves ‘move’ rocks/sediment Wave energy Erosion + Sediment Transport

Wave Energy Wave Energy is typically HIGH Cliff erosion, formation, maintenance, remobilisation of sediments Fine sediments generally absent Depositional areas include: sands, shingles - beach forms Longshore currents (action of waves) leads to movement of sediment Q. What happens when wave energy is low? A. Refashion beach profile

Waves Constructive or Destructive Accretion versus Removal Seasonal Waves are generated by wind, gravity (tides) and? Waves classified into: capillary waves, gravity waves (wind), infra-gravity waves (interaction), long-period waves (tidal) Wave form moves not the water Depth of water shallows closer to the coast, causing waves to break at the surf line - frictional drag causing top of wave to break over bottom Point at which wave ‘touches’ bottom leads to sediment ‘pick up’ and transfer Calm versus storm conditions Seismic activity

Waves Angle of wave approach to coast leads to ‘refraction’ Bays and Headlands - hard versus soft rock - differential erosion More erosive power on headlands than bays or embayments Spatial wave gradients due to differential wave activity lead to development of longshore currents and sediment movement Development of ‘edge waves’ (secondary waves) can amplify the impact of waves at the coast rather than usual dissipation of energy

Wave Refraction refracted wave fronts reduced wave energy in embayment concentrated wave energy on headland concentrated wave energy on headland parallel wave fronts

Beaches Beaches often refashioned rather than removed on high energy coast Beaches tend to dissipate energy - natural coastal defence Depends on materials making up the beach Water running up a beach will return by throughflow or surface flow (dependent on materials) determining sediment removal/transport Beaches and dunes are sediment stores Wave approach angle: Swash and Backwash Sediment moved up, down and along the shore Shore parallel, nomal and rip currents Circulation cells formed leading to ‘cusps’ BEACH BACKWASH SWASH Longshore Drift

Cliff Erosion Cliff Face Geology Sediment Movement Cliff Profile Wave Type Strength Hardness Structure Strata (dip, permeability) Sediment Movement Cliff Profile Wave Cutback Sediment Accumulation/Loss Shore Platform

Remote Sensing, Monitoring, Mapping and Coastal Erosion

Task – Worksheet No. 2 Visualisation http://www.coastal.udel.edu/faculty/rad/linearplot.html Input Wave Data, Examine the Output and Tabulate to see if you can find out what this ‘model’ does and any relationships/patterns that exist