When Relationships Go Wrong - sea defences

632 views

Published on

Some of the problems generated by sea defences

  • Be the first to comment

  • Be the first to like this

When Relationships Go Wrong - sea defences

  1. 1. When relationships go wrong The story of a broken coast
  2. 2. St Bees on the West Coast of Cumbria  Cumbria is a diamond shape  St Bees is at the westernmost tip  It is renowned for its headland – St Bees Head
  3. 3. Management  The location is visited by many field groups as it has good examples of most types of hard engineering protection measures  Promenade, Groynes, Rip rap Rock Armour, Geo netting and a revetment  At Sea Mill lane [to the south of the golf course] there are also gabions.
  4. 4. Which are which?
  5. 5. However the love affair society has with the coast is a troubled one  Like most affairs, over the years attitudes change and what was once a beautiful untarnished thang is now jaded by over exposure.  Before the promenade St Bees was covered in Sand Dunes …
  6. 6.  The natural ecosystem was on blown sand  Consolidated by vegetation  Moving  Flexible  Adaptable but also a valuable asset  Sand and gravel were extracted and the very good natural defences were compromised.
  7. 7. The Response  A variety of different management strategies were introduced primarily a sea wall with promenade, 9 groynes at right angles and a revetment to the South.  Following a collapse of the railway embankment to the far south the slope south of the prom was re-graded, geo- netting introduced to stabilise the slope and the later rock armour added at the toe.
  8. 8. Something for Nothing?  Like most relationships after the initial commitment some investment of time and money is needed to keep things sweet.  Sadly, West Cumbria has suffered from the same budget cuts as elsewhere and the hard engineering is beginning to show signs of a troubled time ahead.
  9. 9. Promenade  The sea wall has experienced some slight movement and in places the mastic between the block has been stripped out by the sea.
  10. 10.  Originally a flat surface stones lie in the remaining hollow No expansion filling
  11. 11.  In places the wall is inadequate and has been overtopped with the beach material re-deposited on the surface
  12. 12.  The sea wall no longer works as a barrier but as an extension to the beach. The retaining blocks behind are now battered.
  13. 13. Further up the sea wall…  A lifeboat ramp has been built. An immoveable barrier which reflects the waves energy, scouring out the beach and transferring the material off shore.
  14. 14. Groynes  Generally these are in a bad state of repair despite some attempt at maintenance.  In some places the buckle under the sheer weight of stones.  In others sections are missing or fixings badly corroded.
  15. 15. You can see some of the new sections – sourced from tropical hard wood?  And in other places holes right through But what is the alternative? Plastic replacements used re-cycled bale wrap but would not biodegrade when they eventually come loose.
  16. 16. North of the promenade  At the end of the sea wall a bridge passes over Rottington Beck and is secured on a block of unprotected concrete.  The energy transferred northwards attacks the mouth of the beck undermining the foundations
  17. 17.  Nature continues to work around the man made obstacles, the beach re-grades and the mouth of the beck cuts out to sea.
  18. 18.  The lined channel accelerates heavily sedimented material towards the coast To the sea
  19. 19.  Despite all this management slips and slides still occur on newly deposited material.
  20. 20. Accretion and deposition  Material moved in shore up the mouth gradually build up on the river bank  At the mouth a small delta appears due to too much material  A spur growth across the mouth
  21. 21. In Conclusion  A natural system was  Natural systems still managed using a hard work hard to overcome engineering solution. the human intervention  Maintenance of the  Micro forms of some of this facility has been the landforms appear poor and in winter it especially at the struggles to keep fluvial / coast interface material in check.
  22. 22. The future?  The adoption of soft engineering solutions are now more widespread  Further south where the cliff material is unconsolidated glacial clay a ‘do nothing’ approach has been utilised effectively.  Imaginative new approaches are still being developed – recycled plastic shuttering to line a different beck's mouth.
  23. 23. Who knows, our rocky relationship may stand the test of time …

×