Unfortunate coincidences of wind and tide

PUBLISHED: 07:44 04 December 2006 | UPDATED: 10:17 24 May 2010

YOUR recent column saw Brian Austin spitting venom, as he announced that the existing sea wall is constructed to take a 41 foot tide and that the tidal range is 43 feet. The Admiralty charts say different. The tidal range is 45 feet and in metric terms a

YOUR recent column saw Brian Austin spitting venom, as he announced that the existing sea wall is constructed to take a 41 foot tide and that the tidal range is 43 feet.The Admiralty charts say different. The tidal range is 45 feet and in metric terms a 41-foot tide should rise only 12.5 metres above datum.September 9 this year witnessed a tide that calmly rose to 13.54 metres above datum, stopping just 450mm below Knightstone Causeway. Previously, the town has been swamped, due to unfortunate coincidences of wind and tide producing wave action capable of pumping a high Spring tide (and a nine tonne boat) over the sea wall and into the town. If the breakwater proposed by Martin Wools had been in place in 1990 (when the Western Lady came ashore), the wave energy that caused the flooding would have been eliminated out in the bay before ever it reached the sea wall. The council's own engineers have already agreed that the proposed breakwater would accommodate a one in 200 year storm.Looking ahead, providing that we get through 2007, when there will be no wall anyway, tide tables suggest it is less likely to happen in the years beyond due to generally galling tides; if we look ahead to 2020 the highest predicted tide is 13.73 metres on September 29 2015. Beyond that date, predicted tide levels keep on falling. However, global warming is the new worry and though much talked about as the driver for the present proposals. It has been variously quantified in terms of rising sea levels, with 600mm in 50 years commonly quoted.If we add a storm surge the picture changes a little. Uphill saw such a surge in March 2006. Caravanners were caught out by a 13.3 metre tide, amplified by a two-foot surge. Even so, they would not have been flooded without the accompanying north westerly creating a wave action that pumped seawater over their sea wall. The town faces the same scenario.The question arises how well will our sea defences work? The Promenade (at Knightstone Causeway) is just about 46 feet above the modern datum level (ADL). If the existing sea wall is raised to its full health and safety level of 1,100mm above the Promenade level, and all openings are gated then it could accept a calm tidal range of up to 15.1 metres ADL. With a breakwater in place a freak storm surge of 1.25 metres, coinciding with the highest tide in September 2015, would be required to overcome a raised sea wall protected by a breakwater.Sadly, in that event, there would be no breakwater-protecting John Crockford-Hawley's 'splash wall'. So if there is a freak storm event at that critical time, then theoretically the JCH splash wall could be overcome by Brian Austin's 'flat water' as it rose to emulate or even surpass the six metre waves that often accompany lesser storms. In that case Brian's house in Alma Street would be awash up to the ground floor ceilings if not above. If it is any comfort to him, I have designed a hydraulically operated retractable wall that not only satisfies the hotel owner's main complaints but would rise three to 17 metres ADL when required. It would be withdrawn into underground storage when not in use. Early retraction would overcome any possibility of the wall holding seawater in the town for longer than necessary. And it would not cost that much more to install. Sadly, although the scheme was sent to the engineers in July, it has been brushed aside by council officers but not for the only one good reason that I would accept. Good as it is, the pop up wall is nautically inferior to Martin Wooll's breakwater scheme. However, it is far superior to JCH's, monstrous Berlin Wall - let the people drag it down. Sign the petition and get your view before the planners now.JULIAN PARRYVictoria Park, Weston

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