Twickenham Society, Special Meeting: Flooding in the Borough

Panel

Douglas Orchard, Chairman, Twickenham Society
John Perry, Chairman, Richmond Environmental Information Centre
Jon Freer, Assistant Director, Environment Directorate, LBRuT
Trevor Baylis – Inventor and Eel Pie Island resident
Dr. Tanya Mathias, Hampton Wick Councillor and Conservative Parliamentary Candidate for Twickenham Constituency

“Join the chorus, make it porous” – John Perry.

On the 11th of November the aforementioned panel assembled for a public meeting set up by the Richmond Environmental Information Centre and Twickenham Society, regarding fluvial flooding (flooding from rainfall rather than tidal) in the borough. The Thames Barrier will no longer be used to defend against fluvial flooding and the floodplain is ever-more impermeable. In light of these facts we must make greater use of alternative flood defences and work on restoring the efficacy of the floodplain to safely process precipitation events.

The meeting commenced with a statistic produced by Sir David King, former governmental advisor, that precipitation will increase some 25% in the Winter and fall a staggering 60% in the Summer. This will undoubtedly put the Thames system under enormous pressure and vastly increase the chances of flooding.

Even without the amplifying effects of climate change, flooding has always been an issue that we have faced. A healthy river naturally floods. A river will periodically spill over onto its surrounding floodplain, dissipating the energy of the floodwaters, depositing its sediment load and allow the excess water to be processed by the land – like a sponge absorbing a spillage. Our impermeable urban landscape conflicts with the once soft, absorbent natural environment the river once flowed through – the main theme of this meeting – hence the slogan, “join the chorus, make it porous.” The most frequently used examples are front drives and patios, which speed up the flow of surface water flow and groundwater flow reaching the channel. A catchment that processes water slowly is far less likely to flood.

Urban sprawl and population growth are synonymous with the majority of the pressures we currently impose on the natural world; none more so than this. Like the majority of the lower Thames, the floodplain within the Richmond borough has been incrementally built upon. We ourselves, have over spilled onto the natural floodplain in direct competition with the river. We have built hard infrastructure to control it, however changes to our climate are making the river harder to live beside.

An early topic of the meeting was the rubble dumped at Ham Fields. Millions of tonnes of rubble was discarded within the 103 acre site produced during the Blitz throughout WWII. This has raised the floodplain. The removal of this rubble was suggested as strategy to bring this section of the floodplain back to its pre-war level, increasing floodwater storage. Orleans Riverside was also discussed with a similar motif. The area that was once the historic Orleans Boathouse has had a layer of topsoil laid over it over half a century ago when residents complained of frequent groundwater saturation. Jon Freer later made the point that the gains in storage would have made negligible difference in dealing with the discharge experienced during previous flooding events. Marble Hill Park has always been poor at dealing with any excess water; floodwaters are not processed and only drain away with low tide.

The meeting moved onto discussing vegetation, principally woodland. There was a general consensus that particularly ancient woodland (existed continuously circa 1600) needs to be better managed and protected as trees absorb and impede the flow of floodwaters. 1 acre of ancient woodland absorbs as much water as 67 acres of grazing pasture. Suggestions of working with land owners to better utilise vegetation were made. The panel was undecided on the impact that dredging would have on the Thames channel, with warnings that dredging in one location may have a negative impact for areas downstream; a tricky issue for hydrological modelling.

Councillor Malthius added that the three weirs at Teddington, Molesley and Sunbury must be maintained to tame future flow. There are plans to convert Teddington Lock to generate hydroelectric power, which is led by a community led project, ‘Teddington and Ham Hydro’ (T&HH). The project was conceived after the Environment Agency (EA), chief environmental regulator of waterways and water infrastructure, invited interest to build hydro turbines on many of their weirs, Teddington being one of them. SLWEN has supported T&HH, however there has been fierce opposition by the board of Lensbury Club.

The Thames Estuary 2100 (TE2100) plan was also discussed; a plan which primarily aims to provide a strategy for dealing with tidal flooding, though other sources of flooding including high river flows as a result of heavy rainfall and surface water flooding. The majority of the panel agreed that this was if not already, becoming out-of-date. Similar to the Thames Barrier. A second Thames Barrier was spoken of as an inevitability, especially with the limited shelf-life of the existing one, which is being deployed at alarming frequency and now only for tidal flooding.

John Freer made clear there were issues in the modelling of the upper and lower sections of the Thames as they have typically been treated as isolated systems. Existing research is now being reevaluated. Freer went on to state that the Environment Agency (EA) has important research in the pipeline relating to flooding that would impact the borough, which should be completed within the next 12 months. On a positive note, legislation is now much tighter on new builds and their porosity. Large buildings are also now required to have water storage tanks for times of extreme precipitation.

The meeting concluded with Councillor Mathius asking the audience whether the flood meeting should become a regular occurrence on the agenda. The audience unanimously agreed.

If you would like to know more about flooding in your area and would like regular flood meetings please tell us at hello@swlen.org.uk.

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