Brize Norton Drainage Strategy

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Brize Norton drainage strategy.

Work so far.

2019 Contents.

Summary 2

Our drainage investigations so far 5

Findings so far 8

Our next steps 9

Appendix 10

1 Summary. We’re working on how to reduce the risk of sewer flooding, pollution, blockages and restricted use of toilets and bathrooms in the Brize Norton area. For us, it’s a priority. We’ll continue to work with our customers and other stakeholders, such as South Oxfordshire District Council, Oxfordshire County Council and private land owners, to take action and make drainage improvements as quickly as possible.

Our drainage strategy work We began our drainage strategy Since 2016, we’ve carried out some work in 2015 by carrying out detailed investigations which have research and regularly meeting with helped us to understand more customers who had been affected about the drainage problems in the by drainage issues, as well as Brize Norton area, and how they stakeholders in the area. might be improved in the future.

From 2018 ** 2015 - 2017 onwards The drainage strategy process We’ve followed the guidance from our Stage 1 Stage 2 Stage 3 Stage 4 regulators, Ofwat and the Environment Agency, ‘Initialise/ ‘Risk ‘Options ‘Intervention’ for our drainage strategy work. The good- prepare’ assessment’ appraisal’ practice process they recommend has four stages*. We completed the first stage in 2016, We're which included a range of background research here into the drainage issues in Brize Norton and Minster Lovell. What this means The town of Witney itself wasn’t part of our Initialise/ Risk Options Intervention stage one drainage strategy investigations. It prepare assessment appraisal was a consideration in this stage as Witney’s Starting the Identifying Developing Implementing sewage treatment works manages Brize process the things that different selected drainage including could prevent options for improvements Norton’s wastewater. However, based on gathering drainage making based on their our stage one work, we’ve now focussed our information improvements, drainage potential benefits and forming and how to improvements outweighing their drainage strategy activities specifically on the relationships manage that work and costs and their Brize Norton area. That’s why we’ve changed with them are value for priority the title of this drainage strategy from Witney stakeholders money (Brize Norton), to Brize Norton.

* ofwat.gov.uk/publication/drainage-strategy-framework-for-water-and-sewerage-companies-to- prepare-drainage-strategies. ** The estimated delivery timeline is dependent on factors including weather conditions, risks and costs, and is, therefore, open to change. Drainage strategy framework stages and timescales

2 Annual rainfall from April 2016 to March 2017 compared to the yearly Work so far Cherwell average across our region

We’ve put together stages two and Cotswolds-East Lee-Chalk three of the drainage strategy process

as their activities are closely linked. So Cotswolds-West Thame Roding Chilterns-East-Colne far in this combined stage we’ve: Brize Norton Lower Lee Ock Upper Thames • Completed some detailed Chilterns-West North London investigations in the Brize Norton Berkshire Downs Cut South London area and identified the others Ramsbury Enborne Lower Wey that need to happen Loddon Nth Downs- Sth London

Nth Downs-Hants Upper Mole Wey-Greensand • Started to assess the risks in the area and how we’ll manage them, such as its growing population and rising groundwater levels Annual rainfall from April 2017 to March 2018 compared to the yearly Cherwell average across our region • Achieved some immediate drainage improvements through Cotswolds-East Lee-Chalk delivering some interventions

Cotswolds-West Thame Roding ourselves, and by working with Chilterns-East-Colne Brize Norton stakeholders to deliver others that Lower Lee Ock are outside of our control. Upper Thames Chilterns-West North London

Unfortunately, we haven’t been able Berkshire Downs Cut South London to complete this combined stage for Enborne Lower Wey the Brize Norton area as we’d hoped Loddon Nth Downs- Sth London

to do at this time. This is because Nth Downs-Hants Upper Mole Wey-Greensand of the unusually dry winter weather

experienced across the majority of our region between 2016 and 2017, and throughout the following winter of Annual rainfall from October 2017 to 2017 and 2018. During these periods September 2018 compared to the yearly rainfall was mainly at, or below, the Cherwell average across our region yearly average for our region, as

illustrated by the maps*. Cotswolds-East Lee-Chalk

Cotswolds-West Thame Roding Chilterns-East-Colne The dry winter weather stopped us Brize Norton from carrying out a number of the Lower Lee Ock Upper investigations that we needed to fully Thames Chilterns-West understand the root causes of the North London

Berkshire Downs Cut drainage issues. Therefore, we’ve been South London

unable to finalise our proposals at this Enborne Lower Wey Loddon Nth Downs- Sth London time, to improve the drainage issues Nth Downs-Hants in the Brize Norton area for the long Upper Mole Wey-Greensand Below average term. rainfall Average rainfall (approximate) Above average rainfall

Source: Thames Water, 2018, based on provisional and unverified data from the Environment Agency. * For more information on current rainfall and groundwater conditions across our region please use this link: 3 thameswater.co.uk/Help-and-Advice/Water-Quality/Where-our-water-comes-from/Reservoir-levels-and-rainfall-figures. Our ongoing work

We’re extending our drainage strategy We’ve joined together with more than Our DWMP will detail the current work in the Brize Norton area. We’ll 40 organisations from across the water and emerging drainage risks continue to assess and respond to the industry to support this groundbreaking across our region, our customers’ drainage risks that we identify through programme. We all recognise the drainage issues and needs, the our ongoing monitoring of rainfall current and future challenges we face operational requirements we have and groundwater levels, together with from factors including climate change and the technological and innovative the flooding trigger levels that we’ve and population growth, and we’re advancements we’ll use. Overall, developed to manage the volume of committed to creating more resilient our DWMP will detail the long-term flows within our sewers. drainage systems to cope with them. interventions we propose to achieve safe and reliable drainage and If the weather is much wetter over The 21st Century Drainage Programme wastewater services within our region, the coming months, we’ll also be has also highlighted the need for water for many years to come. able to finalise our investigations and companies to adopt a consistent drainage strategy for improving the approach to drainage and wastewater Therefore, the long-term drainage drainage issues in the Brize Norton planning. In response, by 2022, and interventions that we select for area for the long term. To develop this at regular intervals after that, each implementation in the Brize Norton our first activity will be to assess all water company in England and Wales area within our drainage strategy, will of our proposed long-term drainage will produce a new document called a also feature in detail within our DWMP interventions. As well as looking at Drainage & Wastewater Management when it’s introduced. The new planning their potential customer benefits and Plan (DWMP)*. This will build on the process and DWMP documentation investment costs, we’ll also assess good-practice drainage strategy will then replace the existing drainage how they support the fundamental framework process we’ve been using, strategy process and documentation. aims of the 21st Century Drainage and the drainage work we’ve already Programme*. carried out.

* You can find out more about the 21st Century Drainage Programme and Drainage & Wastewater Management Plans, by using the following link: 4 water.org.uk/policy-topics/managing-sewage-and-drainage/drainage-and-wastewater-management-plans. Our drainage investigations so far. Since 2016, we’ve carried out a number of investigations in the Brize Norton area. They’ve helped us to understand more about the root causes of the area’s drainage problems, and how they might be improved in the future.

So far our drainage investigations have included:

Customer and Flow and stakeholder asset surveys consultations We checked the performance of our We sent sewer-flooding questionnaires sewer network and the main assets to our customers in the Brize Norton we operate in the Brize Norton area. area. We wanted to hear their We placed three rain gauges and six drainage views and experiences, and flow monitors within the sewers to pinpoint problem locations. across the area. In early 2017, we also carried out CCTV surveys on 600 metres of the sewer network that runs parallel to the river, south of Carterton Road and west of Station Road. This helped us to understand if our assets were contributing to the area’s drainage issues.

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Site Flooding walkovers 'trigger-levels' We investigated beyond our sewer analysis network to find the root causes of We analysed the groundwater levels other drainage issues in the area, that were recorded during periods such as flood water from rivers and when there was flooding and other surface water runoff from drainage issues in the area. We agricultural land that may find its wanted to use this information to way into our sewer manholes. help us to define groundwater thresholds or ‘trigger levels’.

If these levels are reached in future, it could trigger our local response teams to carry out specific work to help prevent the flooding and drainage issues, such as removing excess water from our sewers using lorries that carry large water tanks, (we call them tankers).

6 Immediate drainage improvements. In carrying out our investigations in the Brize Norton area we identified some actions that could achieve immediate drainage improvements. We’ve put a number of these in place already, and supported drainage stakeholders to deliver others, including:

Lining of main sewer section We’ve lined a section of the main sewer in the fields to the east of Station Road, as identified in red on the map. Our CCTV surveys found restrictions in our sewer capacity in this area, caused by tree roots, debris and groundwater entering our sewers through cracks and other defects. A blue arrow indicates the location where we found groundwater entering our sewers in this area.

Lining this section of main sewer will help us to increase the capacity in our sewer network, allowing it to safely transport wastewater. Greater capacity in our sewers reduces the risk of them flooding for our customers, particularly Sewer during wet weather conditions. Location where groundwater is entering sewer

Lined sewer section

CCTV survey

Manholes

Blockages Complete Flow direction

Location where groundwater is entering our sewer network to the east of Station Road.

Groundwater entering our sewer network to the east of Station Road. 7 Findings so far. The drainage investigations that we’ve carried out so far have helped us to understand some of the root causes of the drainage issues in the Brize Norton area. We propose to carry out further drainage activities (we call these interventions), to improve the drainage issues we’ve found so far, in both the short and long term.

Our findings from the drainage investigations we’ve completed so far include:

Maintaining Rising ground- our assets water levels We found We found Our assets such as sewers, manholes and pumps can be damaged Groundwater can enter our sewers when levels are high which in many ways, from age deterioration and blockages, to roadworks reduces their capacity and increases their risk of flooding. There’s and tree roots. We’ve identified a number of defects that are a strong link between the rising groundwater levels across the Brize allowing groundwater to enter our sewers. We’ll continue to Norton area and the drainage issues some of our customers have inspect our assets, and try to fix any problems we find that are experienced, including sewer flooding and restricted use of their causing significant drainage issues. toilets and bathrooms. Our proposed interventions Our proposed interventions • Monitor groundwater levels in our control centre and inform our • Reinforce sewer repairs with watertight lining, removal of response teams if thresholds are passed. The teams will carry blockages and fix pipe defects. out an action plan specifically designed for the area to reduce or • Reprogramme the rising main flow meter at the Brize Norton remove the flooding issue, such as checking sewer water levels sewage pumping station to help us identify when our pumps are and using tankers to take away excess flows from our sewers. operating more than expected. This can mean that groundwater is entering our sewers which shouldn’t be there. We’ll monitor pump performance at our sewage pumping station, specifically Benefits of proposed interventions the reasons behind it potentially operating more than we expect • Give us the capability to predict and prevent some sewer it to, and seek to resolve any issues we may find. flooding issues before they occur, through monitoring • Replace one long-term depth monitor that’s already positioned groundwater levels and sewage pumping station flows. within the area’s sewer network. This will increase our ability to • Increase the capacity of our sewers and reduce the risk of sewer monitor the water levels within our sewers, particularly during flooding when tankering is used to remove excess flows from our periods of wet weather. sewers. • Help us to maintain our wastewater services to customers in the Brize Norton area during wet weather. Benefits of proposed interventions • Increase the capacity of our sewers and reduce the risk of sewer flooding through repairing damaged pipework, sealing manhole Delivery timeframe covers and monitoring the operation of our sewage pumping Proposed for 2018- 2025. station flows. • Help us to maintain our wastewater services to customers in the For more information on the Flooding ‘trigger-level’ survey and Brize Norton area during wet weather. analysis that we carried out as part of this work, please see the Appendix. Delivery timeframe Proposed for 2018- 2025.

For more information on the ‘Lift & Look’ and CCTV surveys that we carried out as part of this work, please see the Appendix.

8 Our next steps. Our next steps are to extend our work in the Brize Norton area. Over the coming months, if this is a much wetter period, we’ll be able to carry out further detailed investigations and finalise our proposals for improving the area’s drainage issues for the long term. This will be the core of our drainage in the Brize Norton area within our reliable drainage and wastewater strategy, and an essential part of the drainage strategy, will feature in services within our region for many Drainage & Wastewater Management greater detail within our DWMP when years to come, will then replace the Plan (DWMP) that we’ll produce for it’s introduced. existing drainage strategy process and our whole region by 2022. documentation. The new planning process, and The long-term drainage interventions DWMP documentation outlining that we select for implementation our proposals for achieving safe and Over the coming months our work in the Brize Norton area will continue to be focused on:

Further drainage Stakeholder investigations engagement Carrying out further drainage Agreeing how we’ll deliver the investigations including checking the interventions that we propose with performance of our local sewage other drainage stakeholders. pumping stations. We’ll make sure that they’re working at their best and not Attending Town Council meetings more than they should be, which can and Council meetings, as required, often mean water is entering our to provide a regular update on our sewers that shouldn’t be there. We’ll findings and progress. We’ll also investigate further any issues we find offer advice on how everyone can to help us to improve drainage in the help improve drainage in the area. Brize Norton area. Flooding Maintaining our ‘trigger-levels’ plan sewers Improving the accuracy of our Ongoing sewer inspections in the flooding warnings or ‘trigger levels’, x area and trying to fix any problems and planning how we can best we find that are causing significant respond if they're triggered. This will drainage issues. help us to manage the flooding in the area and reduce other drainage issues. Replacing a long-term depth x monitor within the area’s sewer network, to increase our ability to monitor water levels, particularly Our next steps during periods of wet weather.

9 Appendix.

‘Lift & Look’ and CCTV surveys

During our recent investigations we undertook ‘Lift & Look’ and CCTV surveys in the Brize Norton area. We went down into our sewer network to inspect the condition of our sewers and to see how they were working.

We carried out CCTV surveys on 600 metres of the area’s sewers and found restrictions in our sewer capacity caused by tree roots and debris, and a point where groundwater is entering our network through cracks and other defects. When we find groundwater entering our sewers we class it as a: seeper, runner or gusher, with a gusher being the most severe and creating the biggest problem for our network’s performance.

The main findings from the surveys Sewer Location where groundwater is include: entering sewer

Lined sewer section Groundwater and sewer CCTV survey Manholes blockages Blockages Our CCTV surveys found groundwater entering a section Flow direction of our sewer in the fields to the east of Station Road. The location is identified by the blue arrow in Figure 1. Reducing Figure 1 Location where groundwater is entering our the number of locations where groundwater enters our sewer network to the east of Station Road. sewers will help to increase the capacity in the sewer network, allowing it to safely transport wastewater. Greater capacity in our sewers reduces the risk of them flooding for our customers, particularly during wet weather conditions.

Additionally, in a number of locations to the east of Station Road, our CCTV surveys found tree roots and debris blocking the sewer network. The blockages are identified as white circles in Figure 1, and Photo 1 provides an example of our findings. Restrictions and blockages can stop our sewers from being able to safely transport an area’s wastewater, they reduce capacity and in some cases can cause sewer flooding.

Photo 1 Example of tree roots within our sewers to the east of Station Road.

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Flooding ‘trigger-levels’ analysis We analysed the groundwater levels that were recorded during periods when there was flooding and other drainage issues in the area. We wanted to use this information to set up groundwater warning signs or ‘trigger levels’ so that we could investigate the impact this groundwater has on our sewers.

We defined red and amber ‘trigger Figure 2 demonstrates the relationship Ongoing monitoring will increase levels’, with red being the most critical between sewer network issues and high our understanding of how our sewer warning sign. A red ‘trigger level’ tells groundwater levels, particularly when network copes with different weather us that sewer flooding is very likely and the red warning ‘trigger-level’ threshold patterns and groundwater conditions. that rapid action is needed to reduce has been reached. This will help us to plan how we can the drainage issues. An amber ‘trigger further reduce sewer flooding and level’ warns that sewer flooding is We propose to continually check and drainage issues for our customers in possible. refine these flooding ‘trigger levels’ the Brize Norton area, now and in the to improve their accuracy, particularly future. If an amber level is reached our local when ‘trigger levels’ have been reached. team will check for unusually high Pump run times Vs Groundwater levels activity at our sewage pumping 24 95 stations. This could be a sign of 94.5 groundwater entering our sewer 22 94 20 network which shouldn’t be there. If 93.5 18 a red level is reached the team will 93

16 lift manhole covers in areas known to 92.5

14 flood, to make sure our sewers have a 92 safe level of water in them, and we can 12 91.5

91 reduce their risk of flooding. 10 Red trigger level Groundwater level (mAoD) 90.5 Pump run time (Hour) 8 Figures 2 is a graphical illustration 90 6 Amber trigger level of one of our flooding ‘trigger-level’ 89.5 4 analysis for the Brize Norton area. In 89 2 Figure 2 the blue line illustrates the 88.5

0 88 changing groundwater level over time, 01/09/12 20/03/13 06/10/13 24/04/14 10/11/14 29/05/15 15/12/15 02/07/16 the green line indicates pump run Flooding incidents Brize Norton pump run times Groundwater level times and the red and orange lines Figure 2 The Brize Norton area flooding ‘trigger-level’ analysis. indicate our proposed red and amber warning or ‘trigger levels’. The yellow dots represent dates on which the Brize Norton area has experienced sewer network issues.