Floodwatch
FLOODWATCH
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.
