Kinson drainage and wastewater strategy
This strategy covers the area served by Kinson water recycling centre (sewage treatment works) including Kinson and West Parley. This area is a part of the Dorset management catchment and the overall Wessex Water's drainage and wastewater management plan.
Kinson is an area in the north of Bournemouth in the River Stour catchment and is predominately sand geology. The River Stour discharges to Christchurch Harbour and onto the Solent waters.
The Kinson 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
Flows to Kinson water recycling centre (WRC) are treated under normal flow conditions and disinfected by UV treatment to reduce the bacteria load to the downstream bathing water. Under heavy storm conditions, flows into the WRC can exceed its capacity. These excess flows will first overflow to storm storage tanks. If these tanks become full, they in turn spill to the river Stour as a storm overflow, as permitted by the Environment Agency, having benefited from screening and a degree of settlement within the storm tank.
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 Kinson area has a high risk for sewer incapacity. The Kinson area also has a frequent spilling storm overflow, which we are investigating.
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 Kinson area has an above average risk for blockages because of sewer misuse.
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.
Sewage treatment works
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. Kinson WRC is approaching capacity to meet its permit.
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)
- storm overflows.
Future challenges in the catchment
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.
Under the Bournemouth core strategy (2012), the Kinson and West Home community area is one of the 11 identified district centres in Bournemouth which will contribute to moderate housing supply. A number of small development schemes will emerge through the development management process. Bournemouth local planning authority has recently commenced a local plan review (2018) which seeks the views from residents for possible additional locations to meet revised housing targets.
Local improvement to the network to accommodate growth, alleviate flooding and improve water quality will be assessed as appropriate and agreed with partners. Improvements to the WRC may be required to accommodate further growth in the future.
Climate change and urban creep
Climate change is likely to increase the frequency and severity 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.
We are working in partnership with Natural England, Bournemouth Borough Council and other partners to investigate and identify solutions to improve drainage currently impacting Kinson Common.
- Improve the pumping station at Golf Links Road to reduce the risk of flooding.
- Investigate and identify solutions for reducing flood risk in the Kinson area.
- Investigate the impact of Wessex Water's operation on Turbary and Kinson Common and identify opportunities to improve surface water management.
- Install phosphorus removal at the WRC to reduce nutrient loading to the River Stour.
- Investigate and, if applicable, identify solutions for improve any frequent spilling storm overflows.
- Reconfigure gully systems in Columbia Road to reduce flood risk.
- Carry out sewer surveys and monitoring to assess the condition and performance of the network.
- Implement identified solutions to reduce flood risk in the Kinson area.
- Review capacity at the WRC, considering growth in the catchment and climate change, and identify and deliver mitigation measures if required.
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.