Flood Watch

The South Woodham Ferrers Yacht Club and Eyotts Sailing Club have through a joint initiative set up the Floodwatch volunteer group. This has been done with the co-operation of Chelmsford Borough Council who seek to involve the community as part of its resilience strategy.

The object of the group is to promote public awareness to the potential risk and offer a data collection service to CBC giving actual water heights at the two participating club gauges. Should overtopping of the sea walls occur make available manned rowing boats as a back up rescue resource.

Total height readings are taken every 15 minutes, three hours before predicted high tide at times of increased risk. Usually following flood warnings from the Environment Agency.

We have recently experienced surge tides that had the potential to result in an overtopping but fortunately due to the timing of max surge and the lower natural tide height it did not get to a level to cause concern.

  • TIDE

This is caused by the gravitational effect of the moon and to a lesser degree the sun. A bulge of water lies on the plane between the moon and the earth, if the sun also lines up in this plane we get a high spring tide. The earth rotates and points on the earth pass through this bulge. As the moons orbit is in the same direction as the earths rotation the tide gets later every day, the moons orbit of 28 days results in the tide being 1/28th of a day later each day, this is about 51 minutes.

The tide is caused by astronomical effects that are predictable and have no meteorological content. As they are predictable tide tables for many years ahead can be forecast to a fair degree of accuracy.

  • SURGE

This is caused by the movement of water based on meteorological effects, atmospheric pressure and winds, they are not predictable therefore forecasts cannot be made, they are as or more fickle than the weather. Data is only available as hindcast from recordings taken from observations.

  • TOTAL HEIGHT

The level of water includes the predictable tide height and the unpredictable surge height. This again is unpredictable and data is only available in hindcast as it contains an unpredictable element.

  • OUR AIM.

From the readings taken and plotted against the predicted tidal height curve an evaluation of the risk of overtopping can be estimated as an increased or decreased risk. On two recent occasions initial readings indicated a potential overtopping but after three readings it became clear the surge was at its maximum at half tide. We were able to report an unlikely chance of overtopping on the data collected. This data was also backed up by the automated tidal data recorders at Felixstowe and Cromer.

Chelmsford Resilience Website

 

 

 Floodwatch Activity 2015

Saturday 21 March 2015
The tides were slightly higher than the predicted 5.8 m caused by the strong winds, but with High Pressure dominating our area 1028  it counteracted a possible surge, probably why   no Flood Alerts were issued by the Environment Agency for the Hullbridge Area.
Below are some pictures taken by one of our Club members Audrey,  at Maldon promenade  illustrating the very high tides;  the seawall being overtopped and flowing into the boating lake; and one of the barges alongside the Hythe Quay.

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Saturday 21 February Sunday 22nd February 2015
Transcript of a message sent to all SWF Floodwatch Team by Email by D.MacEwen
 For interest,  but it may be of concern to some of us on Floodwatch Team,  the spring tides over the next very few days are the highest for decades even the BBC news have featured the high tides. This weekend’s tides are predicted to be the biggest in an 18½ year cycle;   On Saturday   the height of the tide is predicted as 5.8 m at Hullbridge by Easy tide (the Hydrographic Agency) ,and 5.9 m on our Yacht Club tide tables; the seawall is 6.5 m high.  Of minor concern is the fact that on Saturday XC Weather give a moderate to fresh wind from the North West which may cause a slight surge on top of the tide. On Sunday  evening, however, there is a severe force 9 gale forecast but this is from the South West which is likely to  hold back the tide. High tides are approximately at 02:10 and 14:30 on Saturday and 02:50 and 15:15 on Sunday.
Please dust off your Floodwatch gear and be prepared just in case we are called out.

FLOODWATCH  CALLOUTS 2013

SWF Flood Warnings for 5/6 December 2013

 The heights of the tidal  predictions for Thursday 5 and Friday 6 December were exceptionally high, so when the Television news predicted the forthcoming storm, I decided to send out an Email to all of the 24  SWF Floodwatch volunteers giving prior warning to be ready for a call out (copying it to the Chelmsford City Council Emergency Planning Officer Gerry Richardson and our Town Council).

The  dawn, on the morning of  Thursday 5th December was a most vivid orange/red, and remembering the old weather lore, “Red sky at night sailors delight, red sky in the morning sailors warning”, I was glad I had sent out the Email. The high tide at South Woodham Ferrers was at 2.16 in the afternoon and the predicted height was 5.8 m ( the seawalls are 6.5m) It was agreed with Gerry that we would  mobilise, meet at South Woodham Ferrers Yacht Club – Floodwatch Control- deploy teams to Eyott Sailing Club, Clements Green Creek and SWFYC where there are tide gauges, then read and  the actual tide heights at 20 minute intervals, input the data into out computer program, to calculate whether there was a risk of overtopping at High Tide, then  relay the results  to Gerry, our EPO.  In the event the gale force winds were blowing against the incoming tide and “holding it out” so that at high tide in the afternoon, the water was 1 metre less than predicted at 4.8m. It was a good dress rehearsal for what was to come though.

The Environment Agency phone call that night announced that there was now a severe flood warning in place. This time there was no need for a call out, all 12 Floodwatch volunteers  had agreed to meet at 11:30pm. The height of the tide was predicted at 5.5m, lower than the 5.8m in the afternoon. Many of the volunteers were already at SWFYC  by the time I arrived. The tide was already rushing in and was much higher than predicted (see the table below) as  I ‘reported in’ to Gerry, in his Chelmsford Emergency Control ‘bunker’  Gerry said he opened the South Woodham Ferrers Rest Centres needed in case of evacuation. After the second reading, the surge was 2.4 metres above prediction; by now our computer display had turned red indicating this was a serious situation. Gerry in his bunker then asked us to report in every 10 minutes reflecting his concern . This was a very different situation from this morning!

After the fourth reading the Yacht Club had filled up with various people who had a vested interest: the police, James Sinclair and his team from Marsh Farm,  Bob from First Responders representing the Ambulance, and a number of Chelmsford City Council officials. The tide height was now 6metres high, and this was  2 hours before high tide everyone was worried. The computer predicted the water would overtop the seawalls at 1am.

We started to make plans to evacuate ourselves and fall back to Champions Manor Hall,  The Eyott team reported that they had to withdraw up the hill, as the Sailing Club grounds had flooded. I felt for them it was bitterly cold outside.

At the fifth reading the height was 6.2 m very near the seawall top at 6.5m.  The radio suddenly reported that the tide had dropped at Maldon. We did another reading at the Yacht Club there was no change still 6.2m. Had the surge passed ? or had there been a major breach of a seawall somewhere, that had relieved the water ?  When I reported in to Gerry you could hear the relief in his voice.

Over the next two hours subsequent readings remained at 6.2 so we relaxed; the tension eased.  A number of spectators had turned up to look at the river, even a woman in her dressing gown!

At 02:30 the Eyott team reported that the tide was ebbing , by 02:40 it had turned at South Woodham Ferrers Yacht Club. To say we were relieved would be an understatement.

At 02:45 am,  the last radio message to our SWF Floodwatch volunteers was:

 Gerry Richardson the Chelmsford City Council EPO has asked me to pass on his grateful thanks to all of you who turned out yesterday afternoon and then again last night/this morning. He described our actions as “invaluable” to the City Council’s Resilience Plan.

 

The computer readout of the severe flood warning duration (table) .

 

Hours before high tide

Time of reading

Today’s Predicted height M

INPUT ACTUAL HEIGHT

Difference: Predicted “SURGE”

3.00

23:39

2.70

5.4

2.70

2.75

23:54

3.08

5.5

2.42

2.50

0:09

3.45

5.7

2.25

2.25

0:24

3.80

6.0

2.20

2.00

0:39

4.12

6.2

2.03

1.75

0:54

4.42

6.2

1.78

1.50

1:09

4.69

6.3

1.56

1.25

1:24

4.92

6.3

1.38

1.00

1:39

5.12

6.2

1.08

0.75

1:54

5.27

6.2

0.93

0.50

2:09

5.39

6.2

0.81

0.25

2:24

5.47

6.2

0.73

 

Doug MacEwen,  SWF Floodewatch Coordinator