Tuesday, 19 April 2016

Sewage spills into the Hogsmill river

Number to ring in the case of pollution
Rag or sewage around  trees
 The following item will be of most interest to pollution volunteers or PAV's, those who volunteer along the Hogsmill river - either collecting the rubbish, monitoring water quality and the amount of 'rag' at misconnected outfalls - and to some of you that may be considering any of these activities in the future (see previous posts and side tabs on the Hogsmill).

During the early hours of 8.2.16, there was a major sewage spill onto Green Lane recreation ground some of which ended up in the Hogsmill river Grid Reference TQ 20062 67989. This was covered during a February posting hogsmill-sewage-spill and in the Surrey Comet.“What appears to have happened is that a power failure at our Hogsmill treatment works, in the early hours of 8th February, put the inlet pumping station out of action. This, combined with a burst of very heavy rain earlier that night, caused incoming flows to back up and discharge via manholes onto the Green Lane recreation ground. A large area of the recreation ground was flooded with sewage and there is evidence that some sewage entered the river'.

With increased rainfall onto our densly urbanised landscapes, the sewage system is becoming overloaded and smaller spillages from storm tanks, are occurring more frequently. In addition, misconnected residential sewage pipes to the surface water drains are a problem.

This is particularly worrying for riparian dogwalkers; or those who use the river water for irrigating vegetables in the case of allotment holders and the Hogsmill Community Garden (covered in the last post) that has installed a hand pump raising water directly from the Hogsmill.

Today a group of us met to discuss the above issues with Thames Water with fruitfull outcomes. In particular: we left more informed on issues such as sewage leaks and the buffering role of the eight storm tanks at HSW; and hopefully we will be more effective in direct reporting of future problems. We resolved to work towards:
  • Obtaining text messages regarding sewage spills directly from TW, to forewarn our monitoring visits, in the same way that Mogden SW spills 'live' feed onto the TW website for river users;
  • Consider habitat management such as silt washing around the schools currently affected by midge swarms; and to
  • Undertakea fish survey as very little is known about the fish profile of the Hogsmill.
In additon it would seem sensible to undertake a major litter pick of the river corridor to remove all old litter, so that any new rag entering the catchment  can be swiftly dealt with. This should be undertaken as soon as possible to cause least disturbance to growing vegetation.

I now  know where to report surcharged manhole covers (those surrounded by panty and nappy liners)  that are away from watercourses and outside our PAV protocol (our primary concern is with the river, although there is an increased awareness that this is a more widespread problem).

Above all there needs to be a better understanding of the all participants in the planning process regarding Sustainable Urban Drainage or credible attenuation of rainwater (see Flood Risk Position Statement).

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