Nuclear Power Stations in a Warming World
Dungeness in Danger
by Dennis Leggett    

Appendix A                                    

Waves and Surges.

Sea water levels are changed by astronomical and meteorological phenomena..

The changing relative positions of the sun, planets and moon alter gravitational forces acting on Earth. Water responds to them more obviously than do rocks. The oceans align to the forces as the Earth rotates, creating a regular, predictable pattern of Neap, Spring, high and low tides..

Water warming by the sun, and winds created by differences in air pressure, modify tide levels. Warmth expands water causing rises. Lower air pressure allows water to rise. Winds create surface waves. The height that waves can lift water above the current tidal level is related to wind velocity and its fetch i.e. the distance that the wind is operating across the surface..

As a wave travels across the sea surface its water particles are lifted and dropped in circular motion, the particles returning close to their initial positions. At the shoreline the wave 'base' travels less freely than the crest where water particles topple forward on to the shore or sea wall..

If the wave arrives at an oblique angle to the shore line then its wash travels diagonally along the line of the beach moving gravel and sand along in a longshore drift. With some combinations of storm and high tides gravel can be carried up a beach to form ridges. There are visible examples across parts of Pett Level and Dungeness Foreland..

Shallowing seas diffract obliquely approaching waves to a 'face on' approach to the shore. Sea level rise will reduce diffraction, thus longshore drift will increase..

Coastline shape affects local sea levels. The Channel funnels tides, alters wave direction and strength and increases the effects of storm surges..

Storm surges result from sea rise in low pressure conditions and the associated winds. Spring high tides and a slow moving and intense depression with its storms, greatly raise the height and duration of storm surges. The prediction of their occurrence can only be short term and not always reliable. Future predictions are unreliable because past data is not strong and will become increasingly unrelated to temperature, wind and ocean current patterns altered by global warming.

  next:    APPENDIX B    (Floods and Flooding)