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The Mole Tributary System



The Mole Geological System





Urban creep: modern housing and industrial development has caused an ever increasing cover of impermeable surfaces and more connections to the sewer network. Currently, in England, developers have the right to connect new developments to combined sewer systems, without separating foul and surface water, and without regard to the capacity of the sewer to take on a new connection. In Wales, this right was removed in 2019.

Cease the right to connect! Enacting Schedule 3 of the Flood and Water Management Act 2010 would cease the automatic and unchallengeable right for new developments to connect to the sewer network. While SuDS have recently been made mandatory as part of the planning and development process it also essential the Water Companies have the right to turn down connections if local treatment capacity is exceeded.


STW – Sewage Treatment Works


Manage storm runoff : Nature-based solutions such as Sustainable Urban Drainage, or SuDS, “spongify” new developments to hold back rain water runoff and delay or prevent its entry into sewers. This takes pressure off treatment works capacity, reducing storm overflows and hydraulic sewer flooding and often has the additional benefit of biodiversity gain. So this should be a win-win! Happily, SuDS were made mandatory for developers last year so there is progress on this front.


Open Data! Related to the above is the provision of open data and transparent information to communities. Thames Water have made an excellent start with their EDM map which has provided community groups with much needed data to understand the progress being made, or otherwise.


All water companies should commit to providing public, open data in a useable form on the environmental performance of their sewerage network and sewage works. Customers should be able to see how water companies are affecting their areas in real or near-real time, and regulators should have access to this information in order to ensure that water companies are fulfilling their duties.


Unfortunately, pollution of rivers by the water industry as a whole forms just 36% of pollution in rivers. Furthermore, EA data suggests storm overflows are only 4% of the damage to river health. So, while tackling storm overflows is important, it will sadly not restore river health by itself. The Lords asked “is prioritising storm overflows best value for money?” Other measures mentioned so far, like changing consumer behaviour is an absolutely vital part of the whole picture to improve river health.


In addition, other major causes of pollution such as agriculture, road runoff, misconnections and the all pervasive and bioaccumulating “forever chemicals” need to be urgently addressed alongside storm overflows.

Future Water Supply

In 20 years there will not be enough water for the country. Demand will exceed supply particularly in areas that are already water stressed, such as the South East of England. Addressing solutions to this looming crisis must go hand in hand with improving river health. While building more storage and lowering customer demand are two potential opportunities to secure future supply, an holistic approach to water management on a catchment level is required if pollution is to be addressed.

Taking one water company as an example, Sutton and East Surrey Water (SESW) provides water to the bulk of the Mole Catchment (excluding Crawley). It supplies 745,000 people living in 300,000 properties. 85% of the water supplied is abstracted from boreholes in the Chalk and Greensand aquifers. 15% of SESW supply is imported from Bough Beech reservoir, outside the Mole Catchment, which is supplied by abstracting water from the upper reaches of the River Medway.

The company supplies 160 million litres per day, at an average per capita consumption of 151 litres per person per day (above the UK average). The Government target is to reduce consumption to 110 litres per day by 2050, this alone is crucial to the future of sustainable water supply in our area.

Climate change and population growth are set to increase demand and impact supply. Taking this into account, SESW expect to have a surplus of water until 2048 but thereafter demand is set to exceed available supplies. From this point our area will be in increasing water deficit.

SESW have estimated that without carrying out additional actions to reduce consumption or leakage, demand in a dry year will reach an average of around 210 million litres a day by 2080. At the same time, water supply is expected to decrease slightly, due to climate change, to around 190 million litres a day.

In SESW area: by 2075 there will be a shortfall of 46.7Ml/d, or 26.2% of what is needed.


So, there is no question that large scale options are required to bridge the gap between supply and demand by mid-century, only 20 years away.


Leaks are a problem but Water Companies are slowly getting on top of these and meeting targets. It is important that companies model a proactive reduction in wasting water so that they can make better progress reducing customer demand.

Our local water supply company SESW, loses 21 million litres per day of clean water from leaks on their network. The EA has set companies a target to reduce leaks by 50% by 2050 from 2020 levels. Many water companies are meeting interim targets but, while 51 litres per person per day is leaked, the willingness of customers to reduce their own consumption will be reduced.

Final thoughts

We mentioned holistic approaches as being central to solving river pollution. A problem with Thames Water drainage and waste water future plan is that it does not appear to have adopted an holistic catchment based approach. Indeed, TW seem to have sliced and diced catchments so that different parts of one catchments appear in geographically and hydrologically separated basins.

For example, the Mole catchment has been sliced up and the crucial southerly watershed appears to be part of the strategy for Reading and Berkshire.The Mole basin appears to have been sliced in half, not conducive to an holistic approach. By contrast, EA operate catchment officers are focussed on particular river basins. Achieving a joined up approach within catchments and to facilitate operating in conjunction with regulators is central to successfully tackling river basin problems… after all, rivers start a the source and finish at the end of the basin flowing through a myriad of habitats, towns, farms, treatment works and flood defences: all of these knock one onto the next. So it seems the 25 year plan for Surrey has missed a step towards an holistic approach joining up with regulators within at least one catchment.

To finish, in my view, the central message of the Lords committee report is that the Government need now to urgently produce a National Water Strategy that promotes an holistic approach to solving river pollution and providing a secure water supply sustainably into the future.



West Sussex river catchment management project wins share of £36 million for cutting-edge water sector innovation

  • The Catchment Systems Thinking Co-operative, a partnership including Southern Water, the Rivers Trust, 12 water and sewerage companies as well as academia and environmental charities has been named as a winner and will take a share of Ofwat’s £36 million Water Innovation Challenge.

  • The Co-operative seeks to provide grant funding for local project designed to protect local water environments and their surrounding communities & is in partnership with The Rivers Trust.

  • The Water Breakthrough Challenge tackles the biggest challenges facing water and wastewater services, including net zero, reducing leakage, protecting natural ecosystems, and using open data to deliver value to customers, society, and the environment.

01 October 2021 – The Catchment Systems Thinking Co-operative, a partnership of 12 water and sewerage companies including Southern Water, as well as academia and environmental charities, has been announced as a winner in Ofwat’s first Water Breakthrough Challenge.

The Co-operative aims to transform the way in which essential data about health of the nation’s rivers is gathered and shared and its latest project is focusing on the catchments of the Arun and Rother rivers in West Sussex. The partnership has already contributed towards significant pollutant reduction and flood risk management within the other regions around the country where it has been trialled.

As well driving significant improvements to water quality at a lower cost to customers, it has also enabled natural capital benefits to be incorporated at a catchment-wide scale, for example, through enhanced biodiversity, soil conservation and tree planting.

The Catchment Systems Thinking Co-operative aims to encourage the management of water in a holistic way, through an understanding the impact of water management on the local community, as well as the protection of the environment more broadly.

Claire Neale, Principal Catchment Management Specialist at Southern Water said:
“We are delighted to have been awarded this funding which will enable us to continue to deliver on our commitment to improve water quality within the West Sussex catchment and across our regions. This partnership will go a long way to revolutionising local water management practices, through putting the community and the environment first.”

Entries to the Water Breakthrough Challenge were encouraged from water companies in England and Wales in partnerships with organisations in and outside the water sector, including universities and institutes, retailers, start-ups, or small businesses in sectors such as energy, manufacturing, health, or financial services.


About Ofwat’s Innovation Fund

Ofwat has established a £200 million Innovation Fund to grow the water sector’s capacity to innovate, enabling it to better meet the evolving needs of customers, society and the environment.

The Water Breakthrough Challenge is run by Ofwat and Nesta Challenges in partnership with Arup and is the second in a series of competitions funded through the Fund following the Innovation in Water Challenge earlier this year.

Entries were encouraged from water companies in England and Wales, alongside partnerships with organisations within and outside the water sector, including universities and institutes, retailers, start-ups, or small businesses in sectors such as energy, manufacturing, health, or financial services.



Development threats to runoff in the Upper Mole Basin


“With massive housing developments taking place [and proposed] in Crawley and Horsham, what steps are being taken to protect the River Mole Tributary System from further contamination and pollution?”

Richard W. Symonds
The Ifield Society




Good news today regarding SuDS, stormwater management, storm overflows, flood risk and pollution. Mandatory SuDS are coming to England. Developers will no longer have an automatic right to connect stormwater to the sewer but will be required to have sustainable drainage systems approved from a SuDs approval body before starting any construction work that has drainage implications. Well designed and maintained SuDs should reduce need for so many storm overflows.

Read the details here: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1128073/The_review_for_implementation_of_Schedule_3_to_The_Flood_and_Water_Management_Act_2010.pdf