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Heavy Rainfall and Water Quality

As we count the costs of last year's floods misery and find the best candidates for an extra £120m in flood defences, it could be easy to overlook the less obvious consequences of persistent heavy rainfall.


Looking forward to 2013 and beyond to AMP6, it is the water quality demands of the European Water Framework Directive which will be a growing focus for attention.   Heavy rainfall multiplies the challenges for water quality, as diffuse pollution from urban hard surfaces, roads and agriculture is washed into sewers and watercourses and onwards to the sea.


The publication of the 2012 bathing water standards for England showed that heavy rainfall contributed to the failure of a significant number of bathing water sites to meet required standards, including well-known tourist areas in the South West of England.  Despite the £2.5 billion investment by the water companies since privatisation, the Environment Agency indicated that more needs to be done to improve polluted bathing waters in affected areas. 



Meanwhile the annual “Blueprint for Water” progress report, published by a coalition of leading environmental groups, gave the Government a “D – must try harder” rating against the objective “Keep sewage out of homes and rivers and off beaches.  It cited insufficient commitment to real-time monitoring and reporting of Combined Sewer Overflows among the areas for concern.


As water companies develop their AMP6 investment programmes, surely we should go further and consider the need to upgrade CSOs to meet water quality requirements? Improvements to CSOs formed a significant aspect of AMP3, and continued into AMP4, but they were focused largely on removing solids and the gross visual aspects of pollution.   Removing the pollutants that are carried in finer silts and sediments was not addressed.


Using satellite treatment technologies at CSOs can reduce the load of organic pollutants, hydrocarbons and heavy metals flushed into receiving watercourses during peak storms.  Experience from overseas shows that distributed treatment at localized CSO ‘hot spots’ can reap dividends without the need to invest in costly centralised treatment plants, trunk sewers or tunnels.   


Low-power, low-maintenance technologies, such as those using hydro-dynamic vortex separation, have already been proven to be effective , for example,  in schemes supported by Hydro International in Belgium, Italy and the US .


The opportunity should not be overlooked to improve water quality at affected outfalls in the UK incrementally, with minimal disruption and lower costs.


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