Wednesday, 2 December 2015

Flood risk Lower Marsh Lane

Where are the borough's flood defences?

Well according to Strategic Flood Risk Assessment commissioned by the council in 2008 (Jacobs) our main flood defences are the Hogsmill Sewage works, Beverley Brook and the Manor Park and Berrylands Railway Embankments. Jacobs noted that housing should be avoided in Zone 3a (1144 houses currently). There are 57 properties identified in Zone 3b, which is floodplain (Town centre). The Jacobs report presumably went onto inform the Core Strategy 2011, which underpins our Local Development Framework for the borough. The two main policies of interest are:

Policies CS1, CS2, DM1-DM4 2 Manage and reduce fluvial and surface water flood risk in the Borough by ensuring flood risk strategies are kept up to date, guiding new development to areas of low risk where possible and requiring mitigation measures such as Sustainable Urban Drainage Systems. Where development is required within flood risk zones such as Kingston Town Centre, mitigation measures will be required.

Policies CS1, CS2, DM1-DM4 Improve the natural and green environment and local biodiversity through active management and enhancement of local sites and protect natural resources by designating suitable land, requiring new development to increase access to open space and protect and promote biodiversity by tree planting and landscaping.

So if HSW is our main flood defence and a SINC of Borough Importance for Nature Conservation, should we be concerned when parcels of land are being sold off for developement? In fact on December 14th, land along Lower Marsh Lane will go under the hammer.

Flood attenuation strategies are often designed to mimic natural process (biomimicry). Natural ponding occurs behind railway embankments, which is why water attenuation ponds are planned on Elmbridge Meadows where fluvial flooding has occurred. See photos of the River Hogsmill in flood between Rose Walk and Green Lane Recreation Ground, Berrylands, 1937 at http://www.britainfromabove.org.uk  

But is it necessary to spend twice the guide-price of the area currently for sale, on the creation of ponds at an existing nature reserve? Why not retain the flood storage capacity of both sites and use the TW land to mitigate flood risk rather than increase it (see Google image and Flood Risk Map below). This could be achieved by placing land on the Community Asset Register held by the council; except land on this register should satisfy the social and amenity use by the community and is not strictly speaking, for protecting 'life and limb'!
See Environment Agency website indicating that areas in Flood Zone 3a which are to be increased






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