The Environment Agency will close the Thames Barrier this Sunday as part of annual testing -  the Barrier is operated over a full tidal cycle for test purposes once a year.

Built across a 520 metre stretch of the river,  the Thames Barrier has 10 gates including 4 large rising sector gates each spanning 61 metres and weighing 3,700 tonnes.

When the gates have been raised 90 degrees, the Thames Barrier is fully closed in the defence position stopping the tide going into London. As the tide continues to come in, a higher level of water will build up downstream of the barrier creating a differential in water level on either side of the gates.

Shortly after high water or high tide, the gates will be further rotated by 28 degrees (or roughly 2 metres) into what is called the ‘underspill’ position.

Underspill allows the higher downstream water level of the river to rush through underneath the gates to shorten the amount of time it takes for the upstream and downstream water levels to equal. It also creates a white rush effect of water behind each of the gates, attracting many birds which come to feed on the small fish interested in the white rush water and the food it provides. The underspill continues for approximately 2 hours.

The closure is an Open Day which offers visitors a unique opportunity  and insight to see how London remains operational as a modern city - some of the Thames Barrier Teams with displays explaining what they do will be on hand during the day.  The Thames Barrier will begin to close at 6.30am and the gates rise into position.

Approximate timing for the underspill  is 1.45pm and at 4:30pm the Thames Barrier gates will be lowered – all the times are subject to change due to the tides.

Waterbriefing is media partner with the major Environment Agency Flood and Coast 2016 conference and exhibition in Telford from 23rd-25th February 2016. Click here for more information