0:00:29 > 0:00:34In September 2006, television news reported
0:00:34 > 0:00:38that catastrophic floods like those in 1953 were threatening
0:00:38 > 0:00:41to hit north Norfolk again.
0:00:43 > 0:00:47- NEWSREADER: - Parts of the Norfolk coast are at particularly high risk of flooding,
0:00:47 > 0:00:49according to the Environment Agency.
0:00:49 > 0:00:5250 flood sirens across Norfolk were tested this morning.
0:00:54 > 0:00:56Volunteer flood wardens, like Dave Bocking,
0:00:56 > 0:01:00were mobilised on the days between the 6th and the 13th of September.
0:01:00 > 0:01:03Residents waited anxiously.
0:01:03 > 0:01:07With the same high tides predicted as those in 1953,
0:01:07 > 0:01:10disaster seemed a very real possibility.
0:01:10 > 0:01:14This is a first trial of the high tide warnings.
0:01:14 > 0:01:17It looks as though we're going to get away with it.
0:01:19 > 0:01:24To investigate why this coast didn't suffer the catastrophic floods that many had predicted,
0:01:24 > 0:01:29tidal expert Philip Woodworth has brought some high-tech equipment from his lab.
0:01:29 > 0:01:31- Nice to meet you.- Nice to meet you.
0:01:31 > 0:01:34Why was coastal Norfolk on high alert?
0:01:34 > 0:01:37It was on a high alert because there was a predicted high tide
0:01:37 > 0:01:39from the moon and the sun.
0:01:39 > 0:01:43But what people were really worried about
0:01:43 > 0:01:45was the bit that comes on top.
0:01:45 > 0:01:50That's due to the weather, and that's the bit which cannot be predicted a long time in advance.
0:01:50 > 0:01:55Philip's promised me that a bucket, a hosepipe and some water
0:01:55 > 0:01:59are enough to show the dramatic effect of weather on sea level.
0:02:00 > 0:02:03- That's probably enough.- Right.
0:02:03 > 0:02:07- So if you can put your foot on the tube there, Nick.- OK.
0:02:07 > 0:02:10And we'll invent the manometer, or water barometer.
0:02:10 > 0:02:14- So you're tipping in North Sea.- I'm tipping in part of the North Sea.
0:02:14 > 0:02:18- It's rising up the other side. - That's probably enough.- OK, there it is.- Excellent.
0:02:18 > 0:02:23- So the water's at the same height in both sides of the tube.- That's right.
0:02:23 > 0:02:27- Suck at this end of the tube. - What will that be representing, by sucking into that?
0:02:27 > 0:02:32That will reduce the pressure in this part of the tube.
0:02:32 > 0:02:36And if you can put your thumb over the end when you feel ready.
0:02:36 > 0:02:40OK, excellent. We have here a difference in the water level here,
0:02:40 > 0:02:44in this part of the tube down to here, of a good 50 centimetres.
0:02:44 > 0:02:47Now this corresponds almost exactly to 50 millibars.
0:02:47 > 0:02:50A millibar is the unit of air pressure.
0:02:50 > 0:02:55- So it's one centimetre per millibar. - It's an accident of units, almost. An easy thing to remember.
0:02:55 > 0:02:59Now the same effect will happen in the ocean.
0:02:59 > 0:03:02And as the air pressure drops, as it does during storms in the winter,
0:03:02 > 0:03:07the air pressure alone will cause the sea level to rise.
0:03:07 > 0:03:10Or conversely, as the air pressure gets higher,
0:03:10 > 0:03:14that will lower the sea level because it pushes it somewhere else.
0:03:14 > 0:03:20And that's exactly what happened to prevent the predicted floods of 2006.
0:03:20 > 0:03:23The weather was good, atmospheric pressure was comparatively high,
0:03:23 > 0:03:25pushing the sea level down,
0:03:25 > 0:03:29counteracting the effects of the very high tide.
0:03:29 > 0:03:34In January 1953, the opposite was true.
0:03:34 > 0:03:38A higher than usual tide coincided with low air pressure
0:03:38 > 0:03:40due to a deep depression out in the North Sea.
0:03:40 > 0:03:42It was the resulting sea level rise,
0:03:42 > 0:03:48combined with storm-force onshore winds, which caused the flooding disaster.
0:03:49 > 0:03:54Dave Bocking was 18 years old when the flood hit his village, Snettisham.
0:03:54 > 0:03:58It's terrifying, very, very terrifying.
0:03:58 > 0:04:01The sea has no friends.
0:04:01 > 0:04:06You know, it will take whatever's in its path.
0:04:06 > 0:04:09A lot of my best friends all got drowned.
0:04:09 > 0:04:1229 people got drowned down here.
0:04:12 > 0:04:17This was why I became a flood warden, because I had seen it before.
0:04:17 > 0:04:19I come down sometimes,
0:04:19 > 0:04:22and sit and cry.
0:04:23 > 0:04:25I've done that many a time.
0:04:28 > 0:04:31For the time being, the flood warning sirens stay silent.
0:04:31 > 0:04:37But meteorologists predict that a high tide and a low-pressure weather system
0:04:37 > 0:04:40coincide at least once every 250 years.
0:04:42 > 0:04:45It's clear that this land is borrowed from the sea.
0:04:46 > 0:04:49One day soon, she may be back to claim it.
0:04:56 > 0:04:57Subtitles by Red Bee Media Ltd