Monday, March 01, 2010

FLOODING FEARS

From Deputy Town Mayor Coun Ben Nobbs, Brigg Flood Warden

We had a flood alert from the Environment Agency at about 7.30pm on Friday evening.
The river was well down on Friday afternoon but rose very rapidly and when I went out (at about 7pm) it was already rising rapidly. The low tide in the Humber was at 11pm and the river was about one foot below the Cadney road at that time. The last time I checked it was at midnight and it did not seem to be rising any more, but it did come over onto the tow path below Lidl's later on (presumably at high tide, 5am).
If it had rained yesterday (as forecast) I am sure it would have flooded Brigg but we escaped!
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2 comments:

Ken Harrison said...

One of two particular annual natural danger points for potential flooding occurs later this month.

Tides are created by the gravitational pull of the Moon and to a lesser extent by the Sun.

During a lunar month the Sun and Moon pull in roughly the direction on two occasions. This combined pull gives rise to Spring Tides during which high tides and higher than normal, while low tides are inversely lower than average. During the intervening period and to the extent when the Sun and Moon pull in opposings directions we get Neap Tides - ie the tidal range is comparatively less.

However, during the Spring Equinox and the Autumn Equinox (when the Sun is directly over the Equator)the Sun and Moon's gravitational pull on tides is particularly strong.

March 21/22nd is the Spring Equinox and consequently the Sun and Moon are signifiantly in-line and create, assuming all facts remain constant, an enhanced Spring Tide.

Owing to the fluidity of oceans, the combined gravitational pull is naturally deferred by about 3 days after an Equinox, so (without checking my tide tables) around the 25th March should see a very high range of tidal swings.

Strong on-shore winds can and do develop higher than expected high tides; similarly, an atmospheric low pressure area can offer the tide more freedom to rise (conversely, a high pressure, can push down at tide level. In addition, around North Lincs, heavy rain run-off can increase a river's volume.....this makes the River Ancholme especially vulnerable as a rising river level can get trapped in a position where the sluice gates at South Ferribly are closed, while the water run-offs from the local dykes are released.

Therefore, the worst scenerio for around 25th March (check tide table) will be a low pressure area over the region; a strong on-shore wind and for North Lincs to experience heavy rain a few days in advance of the Equinox.

If these combinations do occur then we could well get both coastal flooding (straight off the North Sea) and riverine flooding from the River Ancholme unable to contain its water volume.

1 March 2010 at 23:10
Ken Harrison said...

If anyone is interested:
Apart from everything whizzing about in space and travelling around each other, which gives rise to the Neap and Spring tides...according to the relative position of the Sun and Moon ....slimmers may find its useful to weigh themselves at times of Spring Tides...the gravitational pull also has a reducing affect on body weight!! Only a tiny amount, so don't get too excited!!!

However, some reasons which explain why expected Spring and Neap tide heights are not constant..ie, look at tide tables any you will see that they vary on a monthly basis..are:

1. The Earth's relative distances from the Sun and Moon are not constant...so the 'x' factor of gravitational pull will vary.

2. And a little appreciated aspect is that the Earth orbits the Moon!!! Yes, the Earth orbits the Moon...although, the Moon also orbits the Earth.
Obviously, the Moon's orbit is much more prounouned, but the Earth makes a small gesture of orbitting the Moon in a kind of helixical dance through space.

This combined orbitting has a special name, which I've forgotten at the mo'.

3 March 2010 at 09:53

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