Bridgwater drainage and wastewater strategy

Bridgwater drainage and wastewater strategy

This strategy covers the area served by Bridgwater (Chilton Trinity) water recycling centre (sewage treatment works), including Bridgwater and the surrounding villages of Westonzoyland, Middlezoy, Othery and Ashcott. This area is a part of the Somerset management catchment and Wessex Water’s drainage and wastewater management plan.

Catchment background

The area

Bridgwater is situated on the edge of the Somerset Levels on the banks of the River Parrett where it is highly tidal. The River Parrett discharges to the Bristol channel just 16km downstream at Burnham-on-Sea. The area is predominately clay and flat, generally below 10m elevation, and is typical of the area with channels constructed to drain the levels.

Sewer network

The Bridgwater area has both combined and separate sewer systems to convey wastewater, sewage from homes and businesses, and storm water, rainwater collected from roofs and yards. Under heavy storm conditions, where the sewer conveys both wastewater and storm water, 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 Bridgwater water recycling centre (WRC) is treated and disinfected by UV treatment to reduce the bacteria load to the downstream bathing water at Burnham-on-Sea.

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 entering the sewer systems.   

The Bridgwater area has an above average risk for sewer incapacity however it does not experience widespread and frequent flooding as a result and does not have any 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 Bridgwater area has a high risk for blockages and has suffered sewer flooding in the past because of sewer misuse.

Asset condition

Sewers are inspected to assess their 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 above average risk compared to the rest of 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 sewer flooding. Where heavy rainfall occurs, overland flow collects runoff into rivers or low points on the ground. See the Environment Agency flood maps for more details.

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. Bridgwater WRC is within capacity to meet its permit.

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: 

  • pollution
  • unauthorised wastewater spills or leaks
  • misconnections (when wastewater from household is incorrectly connected to the surface water sewer)
  • storm overflows.

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 (2011) identifies Bridgwater as the principle focus of growth for the Sedgemoor district. Housing and employment growth is and will continue to be delivered within the existing town and through a strategic urban extension to the north east. Ashcott and Westonzoyland are identified as 'key rural settlements' with limited development to support local growth. Limited growth is planned at the 'other sustainable settlements' of Middlezoy and Othery.

The emerging draft local plan (2017) retains an urban focus with Bridgwater continuing to be the main location for the district's growth. Delivery of this growth through the plan period to 2032 will be through ongoing delivery of committed sites, infill and redevelopment in the existing urban area and through new strategic greenfield allocations adjacent to the existing urban area. A significant driver of growth in this location is the proposed new nuclear power station at Hinkley Point which will boost demand for housing. 

Localised improvements to the sewerage network and WRC may be required to accommodate this growth, especially as the development associated with Hinkley Point becomes more defined.

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. 

Wetter winter periods could see an increase in extensive river flooding like that seen around Bridgwater in 2013/14. This could inundate the combined sewer networks and cause surface water and sewer flooding. Changing patterns of summer storms could affect the frequency and volume of storm overflows' spills and consequently impact on the river and bathing water quality downstream.

Urban creep can also pose a challenge for managing our drainage and wastewater networks. This is when existing households extend or build over gardens for 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.

Strategy

Partnership working

We are working in partnership with the Environment Agency, Councils and other stakeholders through the Somerset Levels and Moors flood action plan to understand the risk of flooding in the Bridgwater catchment and to identify options to reduce it as well as working in partnership on specific projects. We are also working in partnership with Somerset county council to trial integrate urban drainage management to improve flood risk beyond our assets.

Short term

  • Deliver the £39 million project of sewerage infrastructure improvements in and around Bridgwater to improve the bathing water quality at Burnham-on-Sea and drainage in Bridgwater.
  • Investigate the condition of Bristol Road rising main and, if required, carry out improvements.
  • Work with customers and the public to promote responsible and correct use of the sewer system to prevent blockages and misconnections.
  • Carry out sewer surveys, monitoring of storm overflows and modelling to assess the condition and performance of the network and new schemes.
  • Improve models to predict flooding and support design of new storage and solutions.

Medium term

  • Continue monitoring, modelling and assessment of sewer network considering domestic and industrial development.
  • Investigate the condition of Colley Lane rising main and, if required, carry out improvements. 
  • Investigate and assess the impact the sewerage system and WRC has on the downstream bathing water at Burnham-on-Sea.
  • Work with partners to develop and appraise options for long term flood risk reduction such as construction of a tidal barrage.
  • Respond and mitigate for development in the area, considering development associated with Hinkley Point C.

Long term

  • Review capacity at the WRC, considering growth in the catchment and climate change, and identify and deliver mitigation measures if required.
  • Deliver additional schemes to improve the water quality at the downstream bathing water. 

We are developing further 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.