Weston-super-Mare drainage and wastewater strategy

Weston-super-Mare drainage and wastewater strategy

This Drainage and Wastewater Strategy covers the area served by Weston-super-Mare Water Recycling Centre (WRC), also known as Sewage Treatment Works, including Brean, Bleadon, Langford and Churchill. This area is a part of the Somerset Management Catchment and Wessex Water’s Drainage and Wastewater Management Plan.

Catchment background

The area

Weston-super-Mare is a seaside town on the coast of the Bristol Channel, in North Somerset at the northern edge of the mouth of the river Axe. The area is predominantly flat with Worlebury Hill to the north and Bleadon Hill to the south and the geology is mainly mudstone with overlying clay soils. 

Sewer network

The Weston-super-Mare area has both foul only and separate sewer systems, where wastewater, sewage from homes and businesses, is collected into the foul only sewer and is conveyed to the WRC. Storm water, rainwater collected from roofs and yards, is collected into a separate surface water sewer which conveys the rainwater to the river. However, in places surface water sewers and highways gullies discharge to the foul sewer. In these cases, under heavy storm conditions, sewer capacity can be exceeded and built in safety valves called storm overflows, permitted by the Environment Agency, can operate to prevent sewer flooding.

Water recycling centre

All wastewater received at Weston-super-Mare WRC is treated. Flows are disinfected by UV treatment to reduce the bacteria load to the downstream bathing waters at Weston-super-Mare.

Current performance

Sewer capacity

Hydraulic incapacity is when the drainage network cannot convey the runoff from heavy rainfall and can lead to sewer flooding. It can be exacerbated by groundwater or other inflows such as surface water entering the sewer system.

The Weston-super-Mare area has a medium risk for sewer incapacity and high groundwater levels from prolonged rainfall periods affect areas of this catchment. The catchment has experienced flooding due to hydraulic incapacity in the past three years but there are no frequent spilling storm overflows in the catchment.

Sewer misuse

Sewer misuse includes flushing anything other than the three Ps (Pee, Poo and toilet Paper) down toilets. Wet wipes, nappies and sanitary products should not be flushed regardless of their labelling. Fats, oils and grease should not be poured down sinks in the kitchen, as this creates ‘Fatbergs’. Sewer misuse can lead to blockages which can cause sewer flooding.

The Weston-super-Mare catchment has medium risk for blockages and has experienced sewer flooding due to blockages in the past three years.

Asset health

Sewers are inspected to assess the condition using a risk-based approach, using the likelihood of it failing and consequence of failure. The sewers in the worse conditions are prioritised for more frequent inspection or rehabilitation.

The risk profile for the condition of the sewers in this area is at medium risk for the Wessex Water region.

Surface water flooding

Surface water flooding occurs when very heavy rainfall overwhelms drainage systems. Responsibility for surface water flooding is complex, but in summary Wessex Water is only responsible for surface water sewers, which conveys rainwater from roofs and yards to the river. Where heavy rainfall occurs, overland flow collects runoff into rivers or low points on the ground. See the Environment Agency flood maps or the North Somerset Council website for more information. 

Water recycling centre

Each WRC has a permit, as agreed with the Environment Agency, for how much water is treated under different weather conditions and the quality of the water that is discharged to the environment.

This WRC is within capacity to meet its permit and was expanded between 2005 and 2010 to accommodate and treat an increase in flow from developments.

Water quality

When untreated wastewater is discharged to a watercourse it can affect the downstream environment including the river and coastal areas. This could be from unauthorised wastewater spills or leaks, misconnections (when wastewater from household is incorrectly connected to the surface water sewer), or storm overflows.

The Weston-super-Mare catchment has experienced a significant pollution event in the past three years.

Future challenges in the catchment

Growth

New developments can cause an increase in wastewater requiring conveyance and treatment. Improvements to the foul sewer system to support new development will be assessed by Wessex Water developers' group and infrastructure charges paid by new developments will fund required upgrades to ensure sewer flooding risk is not increased.

Developments can also increase the area contributing to rainwater runoff to the urban drainage networks, whether it is a surface water or combined sewer, causing an increase risk in surface water and potential sewer flooding. Best practice is to utilise Sustainable Drainage Systems (SuDS). We have a policy that surface water connections to the foul sewer system is not permitted.

The adopted plan (2017) for North Somerset identifies Weston-super-Mare as the focus for growth in the district within the plan period to 2026. A significant proportion of this development will be met at the Weston Villages (Parklands and Winterstoke) Strategic Allocations. In the Weston-super-Mare urban area new housing and employment will be delivered through regeneration. Strategic development proposals at Banwell and Churchill will be subject to further review by the planning authority.

Phased improvements to network capacity will be required to match the rate of development with strategic works programmed to prevent sewer flooding.

Climate change and urban creep

Climate change is likely to increase the intensity of rainfall leading to higher risk of flooding in the future; however, the magnitude and timing of this change is highly uncertain.

Urban creep can also pose a challenge for managing our drainage and wastewater networks. This is when existing households extend or build over gardens and create impermeable area for use such as car parking. This type of growth increases the area contributing to fast runoff to the urban drainage system and can increase the risk of flooding.

As a part of the Drainage and Wastewater Management Plan process, we are producing models to understand how these challenges may impact the area.

Strategy

Partnership working 

We have worked in partnership with Somerset Highways to reduce the risk of flooding in the Milton Hill area by oversizing the underground storage to connect highway gullies and kerb drainage, reducing the risk of flooding to the road as well as properties. We have also worked in partnership with North Somerset Council to extend the superpond and provide additional storage to reduce the risk of flooding using a more sustainable and multi-beneficial solution.

Short term 

  • Model and assess the impact from future development on the network, considering climate change and urban creep, and identify enhancements required to reduce the risk of flooding.
  • Appraise options for integrated urban drainage management approach in Weston-super-Mare to reduce the impact of a pumping station on the local bathing water.
  • Investigate opportunities to remove surface water sewers and highway gullies from the foul sewers to reduce the risk of flooding.
  • Investigate and, where possible, implement solutions to reduce flood risk in areas at risk.
  • Investigate the condition of priority sewers and reline if required to reduce risk of collapse and groundwater infiltration.

Medium term

  • Investigate the condition of the Merrybee rising main and, if required, carry out improvements.
  • Investigate and assess the impact of the sewerage system and WRC on the downstream bathing waters.
  • Deliver enhancements required to accommodate new developments. 

Long term

We are developing long-term options that address and mitigate for climate change, development, urban creep and other future challenges as a part of the Drainage and Wastewater Management Plan process. This could include the use of sustainable drainage systems, new technologies and working with partners more to align long term plans and schemes.