Taunton drainage and wastewater strategy

Taunton drainage and wastewater strategy

This strategy covers Taunton and the surrounding areas including Pitminster, Creech St Michael and Kingston St. Mary, served by Taunton water recycling centre (sewage treatment works). This area is a part of the Somerset management catchment and Wessex Water's drainage and wastewater management plan.

Catchment background

The area

The Taunton area is located on the edge of the Somerset Levels and Moors, in the Vale of Taunton between the Quantock and Blackdown hills. The River Tone runs through the town and joins the River Parrett which goes on to discharge to the Bristol Channel near Burnham-on-Sea. The area is predominately mudstone geology with clay soils and has an average elevation of 25m. 

Sewer network

The Taunton area has predominantly a combined sewer system but in places there are separate sewer systems for 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 Taunton water recycling centre (WRC) is treated before being discharged to the River Tone.

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 Taunton area has an average risk for sewer incapacity however, there are acute capacity issues in places. The Taunton area also has several frequent spilling storm overflows, which we are investigating.

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 Taunton area has an above average risk for blockages from sewer misuse.

Asset health

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 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. Taunton 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. 

Significant ongoing and future growth is planned within the Taunton WRC catchment. The established development plan (2012) identifies the Taunton urban area as the strategic focus for growth. During the plan period (to 2028) growth will be delivered through:

  • major strategic sites at Monkton Heathfield and Priorswood/ Nerrols
  • two major new mixed use urban extensions at Comeytrowe/Trull and Staplegrove
  • redevelopment within the town centre.

Outside of the town, recent development has occurred at Creech St Michael. No allocations are made within the development plan for Kingston St Mary and Pitminster. Work on a new local plan is at a preliminary stage. 

To support this growth and reduce flood risk, strategic improvements will be needed to ensure the network can accommodate this increase in flow.

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 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 Somerset county council and Westcountry Rivers Trust on project SPONGE, an EU funded project to tackle water-related effects of climate change. This project works with communities to create and demonstrate how SuDS can provide benefits for communities and surface water management.

Short term 

  • Install phosphorus removal at the WRC to reduce nutrient loading to the River Tone.
  • Expand the treatment capacity at the WRC to improve treatment and accommodate future growth in the catchment.
  • Twin the sewer from Creech St. Michael to the WRC to improve resilience of the network.
  • Upgrade pumping stations to accommodate future increase in flows from development.
  • Monitor storm overflows and investigate potential solutions for reducing spill frequency.
  • Install telemetry control at Priory penstock to prevent flooding.
  • 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.
  • Review capacity at the WRC, considering growth in the catchment and climate change, and identify mitigation measures if required.

Medium term

  • Construct a storage tank at Monkton Heathfield development.
  • Construct a storage tank at Creech St. Michael to reduce storm overflow spills and risk of flooding.
  • Investigate and identify solutions to convey wastewater from the development at Staplegrove.
  • Investigate and, if applicable, identify solutions to improve any frequent spilling storm overflows.
  • Investigate and assess the impact of the sewerage system and WRC on the downstream bathing water at Burnham-on-Sea.
  • Improve phosphorus removal at WRC further, to reduce nutrient loading to the River Tone.
  • Continue to work with partners to identify opportunities and implement SuDS.

Long term

  • Investigate the strategic options, and if suitable, construct a northern interceptor sewer to convey flows from future developments. 

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.