Tag Archives: FiveThirtyEight blog post

The chances of Canvey Island Flooding during the next 1 in 316 year event, may not be in 316 years time!

Of late on Canvey Island social media websites, it has been noted how some contributors have expressed their view that the island faces a flooding threat from Rainfall, rather than from a Tidal breach or over-topping.

Indeed some have even gone as far as stating that it is Scare-mongering to even suggest the possibility that a threat from Tidal flooding even exists. For this post we will ignore Tidal flooding, leaving those wishing to keep their heads in the sand, and concentrate on Surface Water Flooding.

Following the 2014 Summer Flooding on Canvey Island and the ensuing Flood Investigation Reports, it was recommended that the terminology to indicate the threat of flooding should be altered. That is the existing 1 in 30 year, 1 in 100 year etc possibility of flooding, should be updated so that a more appropriate, more readily understood explanation of the possibility of a flood event is available.

Three years on and it appears that little has changed. This leaves homeowners and businesses oblivious to potential dangers and consequently ill-prepared.

This also leads local authorities into money saving complacency, and having to be reminded of their maintenance responsibilities.

Drain 4.04.17

There are concerns that monies from central government is granted but not strictly allocated to maintenance intended, councils preferring to place grants into central funds.

Some scepticism eludes from the ECC Flood Investigation where maintenance funds were apparently used, and yet the work carried out had little effect on preventing flooding in the following months.

Extracts from the ECC Investigation into the Canvey Island 2014 reveals;

In the period of time between 13:40 and 18:00 one million cubic metres of water fell on the island, which equates to almost the full capacity of Wembley Stadium.

This event was unprecedented,                                                                                                                       and the return period for this rainfall event is estimated at 1 in 316 years or 0.3% chance of it occurring in any given year.

Rainfall on the island may flow a substantial distance before reaching the pumps, through infrastructure owned or managed by a large number of different organisations and individuals and in some cases without a clear understanding of ownership. Any constriction on flow either due to blockage or insufficient capacity for the rainfall event can affect the effective operation of the entire drainage system.

As a result of the relatively densely populated urban areas and large areas of impermeable surfaces the island is especially susceptible to intense rainfall events which result in flash flooding. In combination with the flat topography of the island this means that Canvey is particularly dependent on the designed drainage infrastructure to mitigate flood risk.

Following the longest sustained period of wet weather on record over the winter months, Essex County Council released an additional £1m of emergency revenue funding to deal with highway related flooding.

In mid-February 2014 Castle Point Borough Council put forward its Top 5 flooding sites to Essex County Council, 4 of which were on Canvey Island:

Canvey Seafront area, Lottem Road area, North Avenue area, Town Centre area.

Extensive cleansing, CCTV surveys and jetting of the highways assets was undertaken at all of these locations and where necessary repair works were programmed.  

Arising from these works in the Canvey Seafront Area a larger Surface Water Alleviation Scheme (SWAS) has been identified and put forward for funding (circa £100,000). 

Generally, the drainage system at this location is very flat and prone to heavy silting.

Gullies, catch pits and associated pipework on Canvey Island are cleansed annually as part of the cyclical annual gulley cleanse.                                                                                                                      

There are a total of 5,767 highway and footway gullies in Canvey. 

In 2013/14 5,672 gullies were attended and of these 5,298 (91.8%) were cleansed.

On a personal level, my area of Canvey is amongst the unfortunate 8.2%.

However, returning to the issue of updating the terminology to indicate the threat of flooding should be altered. That is the existing 1 in 30 year, 1 in 100 year etc possibility of flooding, should be updated so that a more appropriate, more readily understood explanation of the possibility of a flood event.

It has been 3 years since the 2014 Canvey Island summer flooding and it appears no new system of flood possibility measurement has emerged.

Meanwhile following the flooding in Houston USA, the FiveThirtyEight blog reveals similar concerns regarding Flood Risk measurement terminology is a talking point across the Atlantic.

The FiveThirtyEight Blog post can be read HERE.

 

 

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