Archive for the ‘Flooding’ Category

Like all residents in the area, you probably experienced a degree of localised flooding following the very heavy rains over the weekend of 27-28 Feb 2010.

For example, several of the back-gardens in Moor Lane were once again swamped as the ground was already saturated and the local drainage could not cope.

Interestingly, the proposed housing site was also somewhat overcome as you can see from the pictures below:

So this begs the question of where will all this water go when there are hundreds of houses on this site?

Answer that, Woking Borough Council.

Did you know that in April / May a survey team were drilling on site, for water, with instructions to go 20 or 25mtrs deep.  The drilling was carried out by a company called “SI Drilling” (www.sidrilling.co.uk)

At the east end of the site they hit water at 4 mtrs and in the west end (at best) they hit water at 7 mtrs down.  At no point did they drill through the water to dry land.   On this basis we can presume that the water table sites 4-7 meters below the land surface for the whole site and higher during the autumn / winter or during unseasonal extremes of rain.

Now here are some thoughts / observations / comments:

• New housing will load the land / compress it causing the water table to rise – with increased hard surfaces and land compression the site will be unable to absorb / hold water as a flood plain should do;
• The new houses are likely to flood so pity the people who have to live there.
• Think about the impact / risk of flooding has on ALL our insurance premiums which is based on post-code assessment of risk.

Further to that, one of our local residents talked with a meter reader and he said that houses over at Quartermaine Avenue have flooded in the past and he said a wall had been built to try a stop the flooding but he also said the stagnant water just sits there and the smell is horrible. So we know that housing to the north of the site is already subject to flooding.

Concerned about the risks the aforementioned resident wrote to the Housing Minister, Margaret Beckett and was passed down the line and had a reply from Brendan O’Keeffe the Surrey Planning Case Officer who advised me to contact my local councillor and /or WBC regards flooding, estate etc. On the 19/6/2009 he received the following reply:

Dear Mr XXXX

Goverment planning guidance in Planning Policy Statement 25: Development and flood risk (PPS25) advises that Flood Risk Assessments should be carried out at all levels of the planning process to assess the risks of flooding from all forms of development. As part of the planning process, the applicant will have to demonstrate to the Environment Agency that the proposed development does not increase the risk of flooding to other properties  and that any risk of flooding is minimized.

In the circumstances I would advise you to bring your concerns about flooding on this site to the attention of the Environment Agency or Woking Borough Council.

Yours sincerely
BJ O’Keeffe
Surrey Planning Case Officer.

The high-level flood risk assessment submitted with the Outline Planning Proposal in 2006 states that

• The development will increase the amount of surface water from the site
• It is proposed that surface water will be collected in balancing ponds and discharged to existing ditches on the east of the site!
• Foul water for the site will be pushed through existing sewers. No review of the existing sewers capacity was carried out at the time.

A map of the existing sewers is shown below:

Foul Water will either drain via gravity to the existing sewers or will be pumped to the south most likely to into node 5101 (see map below for a zoom into the relevant node).

All rights acknowledged.

Woking Borough Council publishes a series of detailed maps that supports the Strategic Flood Risk Assessment (SFRA) for the River Wey catchment. They can be found here: Flooding Maps.

The SFRA examines the causes, transmission mechanisms and effects of flooding as per the diagram below:

I have downloaded and attached the specific maps for our area covering:

• Environment Agency Flood Map – AppendixB1_DRG04
• Detailed Map of River Flooding – AppendixC_DRG04
• Flood Depth Mapping – AppendixD1_DRG04
• Sources of Flooding – Overloaded Sewers – AppendixE1_DRG04
• Sources of Flooding – Surface Water Sewers – AppendixE2_DRG04
• Sources of Flooding – Foul Water Sewers – AppendixE3_DRG04
• Sources of Flooding – Combined Sewers – AppendixE4_DRG04

So what does this tell us?  Well…

1. the eastern part of the proposed development site is part of the functional flood plain with the highest risk of flooding from existing water courses;
2. The western part of the site falls within an area with the highest incidents of flooding from overloading from existing sewers (i.e. the sewer infrastucture needs upgrading);
3. The eastern part of the site falls within Flood Zone 2 & 3 and have a medium or high risk of flooding.

All sites in Flood Zones 2 and 3 will require a site specific Flood Risk Assessment The application of the Sequential Test at these sites must demonstrate that there are no reasonably alternative sites within areas at lower risk of flooding. Following application of the Sequential Test and the demonstration that there are no reasonably available alternative sites in areas at lower risk of flooding, some sites in these zones may require the application of the Exception Test, depending on the vulnerability of the proposed development to flooding to demonstrate that the sites are safe and do not exacerbate the flooding situation – Source: Woking Borough Council SFRA.

The Environment Agency published a useful online tool to help you assess the flooding risk to your property. It can be accessed at:
Flood Assessment Tool

So I had a look at the map for our general area:

Before

Now lets turn on the flood maps…

after

We are potentially an island!

But lets not worry because its a 1:1000 chance of occuring.

That sounds like long odds until you factor in the impact of flooding if there is an increased level of building and concrete hard surfaces deposited in the area.  So what will happen then?

Im not sure but remembering these scenes from a few years ago do any of us really want to find out?

Flooding in Moor Lane

More flooding in Moor Lane