Bourton- On-The- Water Drainage Strategy

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Bourton- on-the- Water drainage strategy.

Our next steps.

2019 Contents.

Summary 2

About our strategy 5

The Bourton-on-the-Water area 8

Our drainage investigations 10

Findings and interventions 14

Our next steps 17

You can help 18

Appendix 20

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 Bourton-on-the-Water area. For us, it’s a priority. We’ll continue to work with our customers and other stakeholders, such as Bourton-on-the-Water Parish Council, Upper Slaughter Parish Council, Lower Slaughter Parish Council, Cotswold District Council, Gloucestershire 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 work Since 2016, we’ve undertaken detailed in 2015 by carrying out research and investigations which have helped us to regularly meeting with customers who understand the drainage problems in had been affected by drainage issues, the Bourton-on-the-Water area, and as well as stakeholders in the local area. find the best ways to prevent them from happening in the future.

Immediate drainage improvements As part of this work we’ve also made some immediate drainage improvements, including fixing sewer defects in Victoria Street and lining some of the local sewers with watertight material. This has significantly reduced groundwater from entering our sewers that shouldn’t be there, increased sewer capacity and reduced the likelihood of sewer flooding in the area during periods of heavy rainfall.

2 Based on our recent investigations • Identifying opportunities to and findings we’re proposing that implement sustainable drainage further drainage activities are carried systems (often called SuDS*), in Our out (we call these interventions), that customer homes and businesses, drainage will help to reduce the drainage issues to reduce the rain water entering proposals in the Bourton-on-the-Water area in our sewers from property roofs the future, these include: • Installing monitors into our • Repairing any further sewer sewage pumping stations so that defects we find, particularly in we can continually check how areas where our inspections they’re operating. identify that groundwater has entered our sewer network

* SuDS are a range of drainage methods that can be used for slowing the speed at which surface water enters our sewer network, and/or redirecting 3 surface water away from our sewers. Examples of SuDS include using water butts, planters and paving that allows water to pass through it. Assessment and selection The long-term interventions that we’re In this drainage strategy proposing will be assessed to make sure document we outline: that their potential benefits outweigh their costs, and then prioritised. • The drainage process we’re using • Our proposals and next steps for making future drainage Those selected will be put in place • The villages that make up the improvements in the area during our next Business Plan Bourton-on-the-Water area period, which is between 2020 and • How our customers can also 2025. Between now and then, we’ll • The things that can cause sewer help to improve drainage in the also continue to work closely with flooding, blockages, pollution and Bourton-on-the-Water area now, local stakeholders to deliver short- restricted toilet use and in the future. term drainage interventions and improvements in the Bourton-on-the- • Our recent work in stage two and You can help Water area. three of the process, particularly the investigations we’ve carried out and what we’ve found benefits costs priorities

4 About our strategy. We’ve followed the guidance from our regulators, Ofwat and the Environment Agency, to produce this drainage strategy.

The good-practice process they We’ve also combined stages two and recommend has four stages*. We three of the process as their activities are completed the first stage in 2016, which closely linked. included a range of background research into the drainage issues in the area.

From 2018 ** 2015 - 2017 onwards

Stage 1 Stage 2 Stage 3 Stage 4 ‘Initialise/ ‘Risk ‘Options ‘Intervention’ prepare’ assessment’ appraisal’

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What this means

Initialise/ Risk Options Intervention prepare assessment appraisal Starting the Identifying Developing Implementing process the things that different selected drainage including could prevent options for improvements gathering drainage making based on their information improvements, drainage potential benefits and forming and how to improvements outweighing their relationships manage that work and costs and their with them are value for priority stakeholders money

* 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

5 In the combined stage The final stage of the process, stage The proposed long-term drainage two and three of the four, will start from 2018 onwards. This interventions will then be reviewed process we’ve: is the intervention stage when we’ll and prioritised against the other carry out some short-term drainage investments we need to make across • Carried out detailed investigations, interventions ourselves, and continue our business, to benefit all of our assessed the risks in the Bourton- to work closely with local stakeholders customers. on-the-Water area, such as its to deliver others. growing population and rising The interventions that we select for groundwater levels, and looked at We’ll also assess the long-term the Bourton-on-the-Water area will how to manage them drainage interventions we propose, to be put in place between 2020 and make sure that their potential benefits 2025. If one or more of our proposed • Found the root causes of the outweigh their costs, which will be paid interventions are not selected, we’ll drainage issues and proposed for by all of our customers. Potential use our increased understanding of options to improve them, based benefits will be assessed based on a the local drainage issues to help us on if they’re long-lasting and range of factors including the number continue our work in reducing flooding value for money of properties affected by drainage in the Bourton-on-the-Water area, and issues, the frequency that flooding preventing service disruptions for our • Achieved some immediate might be expected to occur in the customers. drainage improvements through future, and its severity. delivering some interventions ourselves.

6 Who else is involved? Making drainage resilient in the Bourton-on-the-Water area for the future requires close co-operation with a number of key stakeholders. They include the local councils, private land owners and people with rivers and streams on their land (also known as riparian owners).

Our role is to make sure that the Water that enters our sewers issues that are within our control, sewers and other assets we operate, unnecessarily or by mistake, stops and support stakeholders to deliver such as wastewater treatment works them from working properly. This can those that sit outside of this, so that and sewage pumping stations, are lead to them overflowing and causing together we can make the drainage kept in good condition, work efficiently other drainage issues. We’ll continue improvements needed in the Bourton- and are resilient. to work hard to resolve the drainage on-the-Water area.

Other stakeholders can help to improve drainage in other ways such as:

• Stopping rainwater from running into our sewers from roads and private land Thames Water Customers • Clearing ditches and streams that can cause blockages if left to grow wild Council/ Land and Highways Riparian England Drainage • Connecting pipes correctly from stakeholders owners homes and businesses, rather than into our sewer system. Council/Lead Charities local flood authority Environment Agency

Drainage stakeholders

7 The Bourton-on-the-Water area. We serve over 3,700 customers in the Bourton-on-the-Water area, in Gloucestershire. We transport wastewater through 40 kilometres of sewer pipes and 12 sewage pumping stations. It then ends up at our sewage treatment works, where it’s cleaned and treated before being returned safely back into the environment. We’ve improved and extended our Our sewers have become overloaded The Bourton-on-the- network in the area since it was at times for a number of reasons, Water area includes: originally built, by replacing some unfortunately leaving some of our sewer pipes and building new sewage customers with drainage issues such • Upper Slaughter pumping stations, yet it remains under as sewer flooding, sewer blockages • Lower Slaughter increasing pressure. and restricted use of their toilets and bathrooms. • Bourton-on-the-Water.

Upper Slaughter Lower Slaughter

Bourton-on-the-Water

The Bourton-on-the-Water area*

8 * Source: Contains Ordnance Survey data Crown © copyright and database right (2015) ordnancesurvey.co.uk. Causes of drainage problems. There are many things that In certain conditions, one or more of That’s why we’re working together can cause drainage issues, these can prevent our sewer network with other stakeholders to manage a number of which are not from working as it should and can these issues and to improve drainage sadly cause sewer flooding in our across the Bourton-on-the-Water under our control. They can customers’ homes and businesses, area. Together, we can prevent include: on local highways and in surrounding these unacceptable situations from environments. happening again in the future. • More periods of prolonged and heavy rainfall

• Growing numbers of people, houses and businesses entering the area Intense • Loss of green spaces that rainfall previously provided natural drainage for rainwater as new paths, extensions and houses are built Loss of • Blockages in the sewer network, green often due to fats, oils and grease spaces Population growth being poured down drains Surface and ground water • Misconnected pipework that ﬂooding allows untreated wastewater to enter local rivers and streams

• River water and groundwater Misconnected entering our sewers. properties River Sewer ﬂooding blockages

Causes of drainage problems

9 Our drainage investigations. Over the last couple of years, we’ve carried out many detailed investigations in the Bourton-on-the-Water area. They’ve given us a clear understanding of the root causes behind the drainage issues. They’ve included:

Customer and Flow and stakeholder asset surveys consultations We checked the performance of our We also carried out leak-detection We sent sewer-flooding sewer network and the main assets surveys within the area’s sewer questionnaires to our customers in the we operate in the Bourton-on- network, including undertaking trials Bourton-on-the-Water area. We the-Water area. We placed three of advanced technologies. We tested wanted to hear their drainage views rain gauges and 13 flow monitors temperature-sensing technology for and experiences, and to pinpoint within the sewers across the area, detecting groundwater entering our problem locations. We also met with installed sewer rising main monitors sewers, and leak-detection technology the Bourton-on-the-Water Parish at our sewage pumping stations, for detecting drainage issues in dry Council, Upper Slaughter Parish carried out manhole inspections weather conditions. These surveys Council, Lower Slaughter Parish and surveyed over 3,500 metres of helped us to understand if our assets Council, Cotswold District Council, the sewer network using CCTV. were contributing to the area’s Gloucestershire County Council and drainage issues. gained feedback from other local stakeholder groups.

Site Flooding Impermeable area walkovers 'trigger-levels' surveys We investigated beyond our sewer analysis We measured the size of the network to find the root causes of We analysed the groundwater levels impermeable area that’s connected to other drainage issues in the area, and river levels that were recorded our sewers, including driveways made such as flood water from rivers and during periods when there was out of concrete or tarmacadam, and surface water runoff from agricultural flooding and other drainage issues roofs. As rainwater flows from these land that may find its way into our in the area. We wanted to use this areas into our network, rather than sewer manholes. To help us to do this information to help us define naturally draining away, it reduces the we hosted ‘walkovers’ at flood sites groundwater thresholds or ‘trigger capacity and performance of our with members of the Bourton-on- levels’. If these levels are reached in sewers and contributes to the the-Water Parish Council and Lower future, it could trigger our local drainage issues in the area. The Slaughter Parish Council. response teams to carry out specific surveys enabled us to identify areas in work to help prevent the flooding Bourton-on-the-Water where SuDS and drainage issues, such as remov- could be potentially implemented. ing excess water from our sewers This would help to slow down the flow using lorries that carry large water of rainfall that enters our sewers tanks (we call them tankers). during wet weather, and reduce the risk of sewer flooding. 10 Assessing drainage risks. Alongside our investigations, we’ve assessed the risks to the success of our drainage strategy. We’ve looked at a broad range from We’ve assessed each risk for its climate change and rainfall patterns, likelihood and how severe its impact right through to those risks we’ve could be on the Bourton-on-the-Water found at individual property level. area in the future.

The main risks we’ve identified are:

Rainfall patterns

Stakeholder Population dependency growth

Drainage risks Urban creep Private land issues

Customer inﬂuences

Assessing drainage risks

11 Managing drainage risks. We’re managing the main risks that could prevent our drainage strategy from being successful. A number we can do by ourselves, and others we’re tackling with other stakeholders. By managing these risks together, we’re confident drainage improvements can be achieved in the Bourton-on-the-Water area now, and in the future. The main risks we’re managing are:

Rainfall Population Stakeholder patterns growth dependency Intense, ongoing or above average As the Bourton-on-the-Water area We’re unable to tackle all of the rainfall patterns can overload our increases in size from growing drainage issues ourselves, instead we sewers and contribute to them numbers of people, houses and depend on a number of stakeholders flooding. Some recent climate change businesses, the demand on our sewer to work with us to improve drainage analysis suggests that rainfall could network also increases. across our region. become 20% more intensive by the 2050s*, increasing the potential for We’re managing it by We’re managing it by flooding. And so, we’re working hard Basing our plans on national Fully supporting other stakeholders to to prepare for the effects of climate population data and working with deliver their responsibilities by change and to deliver our services to Local Planning Authorities and providing information that may help our customers during the worst developers to prepare for growth in them, championing their customer weather conditions. the area. This will help us to maintain campaigns and jointly funding our services for all of our customers – activities, where possible. We’re managing it by existing and new. Maintaining our sewer network on an ongoing basis to keep it operating properly, including cleaning it with high-powered hoses to remove silt, and fixing any damaged pipework we find. Also working with other stakeholders to reduce the amount of water entering our sewers. These actions will give us the sewer capacity we need to manage increasing rainfall and help improve drainage in the Bourton-on-the-Water area.

12 * UK Climate Change Risk Assessment 2017: Evidence Report: Flood Risk, Appendix C – Climate Change Projections October 2015. Private land Customer Urban issues inﬂuences creep Some private land activities affect Without knowing it, some of our When green areas are paved over drainage, but sit outside of our customers are contributing to the with impermeable materials that control, such as agricultural land drainage issues in their area. By don’t naturally drain, such as concrete practices and maintaining private pouring cooking fat, oil and grease and tarmacadam, more rainwater ditches and streams. down the drain, and other enters our sewer network and reduces ‘unflushables’ such as wet wipes, its capacity. We’re managing it by sanitary items and cotton buds, our sewer network and reduces its Working with local councils, private sewers can get blocked. We’ve around capacity.We’re managing it by landowners and riparian owners to 80,000 sewer blockages in our region Working with local councils and other make sure that private land practices every year, which prevent sewage stakeholders to make sure that urban support our drainage work. For from flowing freely, and can cause creep is kept to a minimum. We’re example, clearing streams and ditches waste to back up. This can flood also working with our customers to of debris and vegetation helps to streets, rivers, gardens and in the encourage them to use water butts to prevent water flooding from highway worst cases, inside people’s homes. collect rainwater from their property drains entering our sewers. roofs and to use permeable materials Misconnected properties are for new driveways and paths. This will common, a report suggests 140,000 reduce the amount of rainwater properties in the UK are currently entering our sewers and the possibility misconnected*. This means their of flooding during periods of wet drainpipes are incorrectly connected weather. to our sewer network, reducing its capacity and leading to sewer flooding during heavy rainfall. Did We’re managing it by Providing our customers with you information and tips to help us keep our sewers running clear, and working know? with local councils to ensure misconnected pipes are fixed. We’re also encouraging our customers to disconnect rainwater pipes from our You’ll need planning sewers and to use other water-saving permission from your devices to reduce the water entering local council to use our network. impermeable materials in your home improvements.

13 * UKWIR, 2013. Sewer Misconnections: What is the True Non- Agricultural Diffuse Water Pollution Impact? Report 13/SW/01/3, UK Water Industry Research (UKWIR). Findings and interventions. We’ve found the root causes for the drainage issues in the Bourton-on-the-Water area and put together some proposals to improve them. Our proposals consider the risks in the area, the ability to create long-lasting improvements and value for money. We’re confident the options we’re proposing to be delivered in stage four of the process will achieve effective drainage improvements for the Bourton-on- the-Water area for many years to come.

Rising ground- Rainwater water levels from roofs We found We found Groundwater can enter our sewers when levels are high which The downpipes on property roofs can be mistakenly connected reduces their capacity and increases their risk of flooding. There’s to our sewers. Misconnected property roofs located at Springvale, a strong link between the rising river levels that cause rising Beddome Way and further isolated locations, are currently groundwater levels, particularly adjacent to the River Windrush contributing significant volumes of rainwater into our sewer but also across the Bourton-on-the-Water area, and the drainage network. This is reducing the capacity of our sewers and adding issues some of our customers have experienced; including sewer to the area’s drainage and flooding issues. flooding and restricted use of their toilets and bathrooms. Our proposed intervention Our proposed interventions Working with Bourton-on-the-Water Parish Council to: • Monitoring groundwater levels in our control centre and • Investigate if roof drainage can be separated from the sewer informing our response teams if thresholds are passed. The network. It may be possible to do this jointly through customer teams will carry out an action plan specifically designed for the campaigns and the installation of SuDS for our customers in area to reduce or remove the flooding issue, such as checking affected areas. The type of SuDS we propose to be used are sewer water levels and using tankers to take away excess flows planters which would be connected to the downpipes from from our sewers. property roofs, as illustrated. • Installing monitors in our sewage pumping stations to help us identify when our pumps are operating more than we expect them to. This could mean that groundwater is entering our sewers which shouldn’t be there. We’d investigate further to find out the root cause of the drainage issue affecting our sewage pumping stations. Benefits of proposed interventions • Give us the capability to predict and prevent some sewer flooding issues before they occur, through monitoring river levels, groundwater levels and pumping station flows. Existing downpipe • Increase the capacity of our sewers and reduce the risk of sewer flooding when tankering is used to remove excess flows from our sewers. • Help us to maintain our wastewater services to customers in the Bourton-on-the-Water area during wet weather. Proposed SuDS ‘planters’ for misconnected roof drainage. Delivery timeframe Benefits of proposed intervention Proposed for 2018- 2025. • Increase the capacity of our sewers and reduce risk of sewer flooding by limiting the volume of water that enters our sewers For more information on the flooding ‘trigger-levels’ survey and from misconnected property roofs. analysis that we carried out as part of this work, please see the • Help us to maintain our wastewater services to customers in Appendix. the Bourton-on-the-Water area during wet weather. Delivery timeframe Proposed for 2020- 2025. For more information on the impermeable area survey that we carried out as part of this work, please see the Appendix.

14 Maintaining our assets We found Our assets such as sewers, manholes and pumps can be damaged in many ways, from age deterioration and blockages, to roadworks and tree roots. We’ve identified a number of defects which are allowing groundwater to enter our sewers. We’ll continue to inspect our assets and try to fix any problems we find that are causing significant drainage issues. Our proposed interventions • Reinforcing sewer repairs with watertight lining. For more details please see the ‘Leak-detection and CCTV surveys’ section in the Appendix. • Installing new monitors at a number of our local sewage pumping stations (SPS), identified in red on the map, while also analysing the quality of monitored data at our other sewage pumping stations in the area. This will help us to keep a close check on how our sewage pumping stations are working, and alert us to any issues.

Lower Slaughter SPS

Station Road SPS Roman Way SPS

Bourton-on-the-Water sewage treatment works

Bourton-on-the-Water SPS

Proposed sewage pumping station monitor installation. Benefits of proposed interventions • Increase the capacity of our sewers and reduce the risk of sewer flooding. • Improve our capability to monitor how our sewage pumping stations are operating. For example, we’ll be alerted when they’re operating for longer periods than expected. This can be due to too much groundwater entering our sewers and would be investigated further. We’ll also receive alerts when our sewage pumping stations are not operating as they should, and if maintenance or upgrades are needed. • Help us to maintain our wastewater services to customers in the Bourton-on-the-Water area during wet weather. Delivery timeframe Proposed for 2018- 2025. For more information on the leak-detection and CCTV surveys that we carried out as part of this work, please see the Appendix.

15 Immediate drainage improvements. As we developed our proposed options to achieve long-term drainage improvements in the Bourton-on-the-Water area, we also identified some actions that could achieve immediate improvements. We’ve put a number of these in place already, including:

Installing sewage Fixing pumping sewer station defects monitors

We’ve installed rising main monitors and We carried out leak-detection and CCTV This has significantly reduced the volume supporting communication tools at surveys on 3,500 metres of the local sewer of groundwater entering our network and three of our sewage pumping stations, network to identify any issues and defects. will help to prevent flooding and loss of located in Lower Slaughter and We’ve repaired the sewer defects service for our customers in the Bourton-on-the-Water. identified in the main sewer located in Bourton-on-the-Water area, particularly Victoria Street, and relined it with following heavy rainfall. Images from our This will help us to keep a close check on watertight material. CCTV surveys can be seen below. how our sewage pumping stations are working and alert us to any issues, so that we can reduce service disruptions for our customers. Complete

Installing sewage Fixing Complete pumping sewer station defects monitors Groundwater entering our network in Victoria Street before sewer lining.

Complete 16 Our next steps. In 2018 we started the final stage of the drainage strategy process, stage four. This is the intervention stage when we’ll carry out some long-term drainage interventions ourselves, and continue to work closely with local stakeholders to deliver others that are outside of our control. Our first activity is to assess all of planning. In response, by 2022, and Therefore, the long-term drainage our proposed long-term drainage at regular intervals after that, each interventions that we select for interventions. As well as looking at water company in England and Wales implementation in the Bourton-on- their potential customer benefits and will produce a new document called a the-Water area within our drainage investment costs, we’ll also assess Drainage & Wastewater Management strategy, will also feature in greater how they support the fundamental Plan (DWMP)*. This will build on the detail in our DWMP when it’s aims of the 21st Century Drainage good-practice drainage strategy introduced. The new planning process Programme*. framework process we’ve been using, and DWMP documentation will then and the drainage work we’ve already We’ve joined together with more carried out. replace the existing drainage strategy than 40 organisations from across process and documentation. the water industry to support Our DWMP will detail the current this groundbreaking programme. and emerging drainage risks Our chosen interventions for the We all recognise the current and across our region, our customers’ Bourton-on-the-Water area will be put future challenges we face from drainage issues and needs, the in place during our next Business Plan factors including climate change operational requirements we have period, which is between 2020 and and population growth, and we’re and the technological and innovative 2025. We’ll work with our customers committed to creating more resilient advancements we’ll use. Overall, and other stakeholders to implement drainage systems to cope with them. our DWMP will detail the long-term them as swiftly as possible during interventions we propose to achieve that time. Between now and then, The 21st Century Drainage Programme safe and reliable drainage and we’ll also continue to work closely has also highlighted the need for wastewater services within our region, with local stakeholders to deliver water companies to adopt a consistent for many years to come. approach to drainage and wastewater short-term drainage interventions and improvements in the area. Over the coming months our work in the Bourton-on-the-Water area will continue to be focused on: Further drainage Stakeholder investigations engagement Carrying out further drainage Attending meetings with investigations, including checking the Bourton-on-the-Water Parish performance of our local sewage Council, Upper Slaughter Parish pumping stations. We’ll make sure that Council, Lower Slaughter Parish they’re working at their best and not Council, Cotswold District Council more than they should be, which can and Gloucestershire County often mean water is entering our Council, to regularly 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. Bourton-on-the-Water area. Flooding Maintaining our ‘trigger-levels’ plan assets Improving the accuracy of our Ongoing sewer inspections in the flooding warnings or ‘trigger levels’, x area and fixing any problems that and planning how we can best we find, to stop them from causing respond if they’re triggered. This will drainage issues. help us to manage the flooding in the area and reduce other drainage issues. x Our next steps

* You can find out more about the 21st Century Drainage Programme and Drainage & Wastewater Management Plans, by using the following link: 17 water.org.uk/policy-topics/managing-sewage-and-drainage/drainage-and-wastewater-management-plans. You can help. We’ve received a lot of support for our drainage work and we know that some of our customers, and other drainage stakeholders, are already working hard in a number of areas. However, our findings from this stage suggest that there’s still more to do, and by doing it we can improve drainage in the Bourton-on-the-Water area, and across our region, now and in the future. And so, there are lots more things everyone can do to help improve drainage, including taking the following simple steps.

1. Use water-saving 2. ‘Bin it – don’t 3. Check your gadgets block it’ plumbing There are a number of water-saving We’re working hard to keep our Some of our customers have their gadgets you can use in your homes sewers running clear from nasty rainwater pipes incorrectly connected and gardens, and some are free blockages and to help people to our sewer network. This plumbing to our customers. By reducing the understand what can and can’t mistake reduces the capacity of amount of water entering our sewers go down the drain. Things such as our sewers and can lead to flooding we can free-up capacity to manage cooking fat, oil, food waste, wet wipes during heavy rainfall. We’re providing heavy rainfall, and reduce the volume and make-up pads all mix together our customers with information that’s flushed away for treatment. in the sewers to create blockages and tips to help them work out if By connecting your downpipes to These can grow so large that the their property is connected properly, a water butt you can collect a free sewers become completely blocked. and what to do if it isn’t. We’re source of water for watering your Once this happens the consequences also working with local councils to garden. This could not only help to can be devastating, as raw sewage is ensure misconnected pipes get fixed. save money on your water bills, but forced back up into people’s homes. You can check if your property is also help us to reduce the amount If it’s not poo, pee or paper, please connected properly by using this link: of rainfall entering our sewers. To ‘Bin it – don’t block it’. find out more, and to apply for our connectright.org.uk. free water-saving gadgets please use For more information on how you these links: can help us, please follow this link:

freebies.thameswater.co.uk. thameswater.co.uk/binit.

thameswater.co.uk/My- Account/ Customer-Offers/ Customer-Offers.

18 4. Choose drainage- 5. Take care of friendly home watercourses improvements on your land If you’re planning to pave over If you own land or property next to your garden for a driveway or an a river, stream or ditch you’re called extension, choosing materials that a ‘riparian landowner’. This means allow rainwater to drain through you’ve certain responsibilities for them will help us to tackle drainage taking care of the watercourse on issues in your area. You’ll need your land, and preventing its water planning permission from your local from entering our sewer network. To council to use impermeable materials find out more about the duties of a in your home improvements, such as riparian owner please refer to this concrete or tarmacadam. They don’t government guidance: allow rainwater to drain away, instead it can run into our sewer network. gov.uk/government/ For more advice on drainage-friendly publications/riverside- home improvements please follow ownership-rights-and- these links: responsibilities. planningportal.co.uk/ info/200130/ common_ projects/45/paving_your_ front_garden. developers.thameswater.co.uk.

19 Appendix.

Leak-detection and CCTV surveys During our investigations we carried out leak-detection and CCTV surveys in the Bourton-on-the-Water area. We went down into our sewer network to inspect the condition of our sewers and to see how they were working. Our leak-detection surveys identified provided us with a temperature The CCTV footage we recorded in locations where groundwater is highly measurement every six minutes and 3,500 metres of the local sewer likely to be entering our sewer network, were recording from early December network also confirmed points where which shouldn’t be there. As part of 2016 to late April 2017; a period when groundwater is entering, or potentially this work we also undertook a number high groundwater levels and high river entering, our sewer network through of trials with advanced leak-detection levels usually occur. cracks and other defects. When technologies. In particular, we tested we find groundwater entering our a leak-detection technology designed Our trial found that groundwater sewers we class it as a: seeper, runner to find sewer defects, and other was likely to be entering our sewer or gusher, with a gusher being drainage issues, during dry weather network at, or near, the temperature the most severe and creating the conditions and a temperature-sensing sensors positioned in Lower Slaughter, biggest problem for our network’s technology designed to help detect Victoria Street and Clapton Row. The performance. groundwater entering sewers. trial results also helped us to further target our leak-detection and CCTV Completing these surveys and trials As part of our temperature-sensing surveys. We’ll continue to research the helped us to understand if our assets technology trial we placed 19 sensors effectiveness of temperature sensors were contributing to the drainage into the sewers around the Bourton- for detecting groundwater in our sewer issues in the Bourton-on-the-Water on-the-Water area. The sensors network. area. The main findings from our surveys include: Victoria Street and Sherborne Street We found that groundwater is Reducing the number of locations sewer network. Greater sewer capacity entering our sewer network at several where groundwater enters our sewers reduces the likelihood of sewer locations in Victoria Street and will help to increase capacity in the flooding for our customers. Sherborne Street. A number of main sewers and side connections were affected, as highlighted in red in Figure 1.

Our surveys identified runners between manholes SP16206602 and SP16207601 on Sherborne Street, and runners and gushers at several locations between manholes 1 SP16207601 to SP16207503 on Victoria Street. Our leak-detection surveys also indicated the potential for groundwater to enter our sewer Figure 1 Locations where groundwater is entering our sewer network from a number of side network in Victoria Street and Sherbourne Street. connections on both Sherborne Street 20 and Victoria Street. Clapton Row area We identified that groundwater Street to Clapton Row. Main sewers of locations between manholes is entering our sewer network at and side connections were affected SP16208404 and SP16208407, and a several locations in Clapton Row, by groundwater in this location, as gusher plus further signs of groundwater and the sewer that runs parallel with highlighted in red in Figure 2. We found at several points between manholes

the River Windrush from Victoria runners and gushers at a number SP16208502 and SP16208407.

0 2

Honeystone

Applegarth

Cott 9

Wa yside Cott

1 2 8 s r .5 la d m C e o M tt e h T

Figure 2 Locations where groundwater is entering our sewer network in the Clapton Row area. High Street area Our surveys found that groundwater Figures 3 and 4. We found a gusher in We also found seepers, runners and is entering our sewer network at the sewer from manhole SP16204902 gushers in the section of sewer from several locations in the High Street to SP16204901, and a runner in manhole SP16207702 to SP16209501. area. The main sewers affected by the the sewer located from manhole groundwater are highlighted in red in SP16205901 to SP16206901.

Figure 3 Locations where groundwater is entering our sewer in upper

High Street.

6 s 3 Chilverstone e Figure 4 Locations where groundwater is entering our sewer in High 21 Street. Upper Slaughter Our leak-detection surveys indicated to SP15235303 and SP15236302 that groundwater is likely to be entering to SP15236306. An affected side our sewer network at a number of connection was also found to be located locations in Upper Slaughter, as between manholes SP15235303 and highlighted red in Figure 5. The affected SP15235302. main sewers include SP15235201

d For

Figure 5 Locations where groundwater is entering our sewer network in Upper Slaughter. In Upper Slaughter, we identified a potential for groundwater to enter runner in the main sewer from manhole our main sewer between manholes SP15238201 to SP15238102, as SP16230001 and SP16220901, also highlighted red in Figure 6. Our Leak- highlighted red in Figure 6. detection surveys also indicated the

Upper Slaughter

i v

Figure 6 Locations where groundwater is entering our sewer network between Upper and Lower Slaughter.

22 Lower Slaughter We found that groundwater is entering SP16224503 to SP16224504, highlighted red in Figure 7. Additionally, our sewer network at several locations SP16223502 to SP16224505 and we found that the chamber for in Lower Slaughter. The affected SP16225602 to SP16225502. Our manhole SP1622461C is affected by main sewers in west Lower Slaughter surveys further identified runners and groundwater, also highlighted red in include SP16223604 to SP16223603, evidence of blockages from roots, as Figure 7.

ye er E Riv

Figure 7 Locations where groundwater is entering our sewer network in west Lower Slaughter.

In east Lower Slaughter, we found Slaughter sewage pumping station. between manholes SP16226501 and parts of the main sewers to be affected These locations are highlighted red in SP16226502, and also highlighted red by groundwater from manhole Figure 8. We also found some sewer in Figure 8. SP16226501 to SP16226502, and side connections to be affected by from manhole SP16226504 to Lower groundwater, these were located

Figure 8 Locations where groundwater is entering our sewer network in east Lower Slaughter.

23 Impermeable area survey. Impermeable ground doesn’t allow rainwater to drain through it naturally such as driveways made out of concrete or tarmacadam, and roofs. Instead the rainwater from these areas pools together and often flows into our sewer network.

This additional water reduces the our sewers is the equivalent size of one capacity of our sewers, stops them football pitch. Most of the rainwater from working properly and contributes from roofs comes from properties to the drainage issues in the local in Springvale and Beddome Way, area. Our survey measured the size as highlighted in red in an example of the impermeable area in the extract from the survey in Figure 9. Bourton-on-the-Water area, and we investigated its impact on our sewer We propose to investigate the network. possibility of removing roof drainage from our sewer network with Our survey findings: Bourton-on-the-Water Parish Council, Upper Slaughter Parish Council, Our impermeable area survey Lower Slaughter Parish Council, indicated that significant volumes of Gloucestershire County Council and rainwater, caught from the roofs of Cotswold District Council. This could local properties, flows into our sewer increase capacity in our sewers and network rather than draining away reduce the risk of flooding incidents naturally. The total area of roofs which for local residents. allows rainwater to incorrectly enter

Industrial Park

Figure 9 Sample from impermeable area survey results.

24 x

x Flooding ‘trigger-levels’ analysis. We analysed the groundwater levels and river levels that were recorded during periods when there was flooding and other drainage issues in the Bourton-on-the- Water 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 10 demonstrates the Ongoing monitoring will increase levels’, with red being the most critical relationship between sewer network our understanding of how our sewer warning sign. A red ‘trigger level’ tells issues and high river levels, particularly network copes with different weather us that sewer flooding is very likely and when the red warning ‘trigger-level’ patterns and groundwater conditions. that rapid action is needed to reduce threshold has been reached. This will help us to plan how we can the drainage issues. An amber ‘trigger We propose to continually check and further reduce sewer flooding and level’ warns that sewer flooding is refine these flooding ‘trigger levels’ drainage issues for our customers in the possible. to improve their accuracy, particularly Bourton-on-the-Water area, now and in when ‘trigger levels’ have been the future. If an amber level is reached our local reached.

team will check for unusually high 4 /'5 3'7 Groundwater levels Vs Flooding incidents in Bourton-on-the-Water 3'5 /'44 activity at our pumping stations. 553'3 0.60.6 4.84.83'1 /'4 4.64.63 0.550.55 4.44.42'7 /'34 This could be a sign of groundwater 4.24.22'5 0.50.5 442'3 /'3 3.83.8 0.450.45 2'1 3.63.6 entering our sewer network which 3.43.42 /'240.40.4 3.23.21'7 331'5 /'20.350.35 2.82.81'3 shouldn’t be there. If a red level is 2.62.61'1 /'140.30.3 2.42.41 2.22.20'7 /'10.250.25 220'5 reached the team will lift manhole 1.81.8 RedRed triggertrigger levellevel 0.20.2 0'3 /'04

1.61.6 !!*+ 1.41.40'1 AmberAmber triggertrigger levellevel 0.150.15 1.21.20 /'0 covers in areas known to flood, to make 11/'7 0.10.1 /'5 /'/4 River Level (m) *+& !"*,2(+

0.80.8 River level (m) /'3

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'),#','-#%! /2(/0(08/0 00(/0(08/0 08(/0(08/0 16(/0(08/0 /3(/1(08/0 01(/1(08/0 1/(/1(08/0 17(/1(08/0 /7(/2(08/0 05(/2(08/0 13(/2(08/0 /0(/3(08/0 /8(/3(08/0 06(/3(08/0 14(/3(08/0 /2(/4(08/0 00(/4(08/0 08(/4(08/0 16(/4(08/0 /3(/5(08/0 01(/5(08/0 1/(/5(08/0 17(/5(08/0 /5(/6(08/0 03(/6(08/0 11(/6(08/0 2/(/6(08/0 /6(/7(08/0 04(/7(08/0 12(/7(08/0 20(/7(08/0 /7(/8(08/0 05(/8(08/0 13(/8(08/0 /1(0/(08/0 0/(0/(08/0 07(0/(08/0 15(0/(08/0 /2(00(08/0 00(00(08/0 08(00(08/0 16(00(08/0 /4(01(08/0 02(01(08/0 10(01(08/0 18(01(08/0 /0(/0(08// /8(/0(08// 06(/0(08// 14(/0(08// /1(/1(08// 0/(/1(08// 07(/1(08// 15(/1(08// /4(/2(08// 02(/2(08// 10(/2(08// 18(/2(08// /5(/3(08// 03(/3(08// 11(/3(08// 2/(/3(08// /7(/4(08// 05(/4(08// 13(/4(08// /0(/5(08// /8(/5(08// 06(/5(08// 14(/5(08// /2(/6(08// 00(/6(08// 08(/6(08// 16(/6(08// /3(/7(08// 01(/7(08// 1/(/7(08// 17(/7(08// /4(/8(08// 02(/8(08// 10(/8(08// 18(/8(08// /6(0/(08// 04(0/(08// 12(0/(08// 20(0/(08// /7(00(08// 05(00(08// 13(00(08// /1(01(08// 0/(01(08// 07(01(08// 15(01(08// 03(/0(08/1 11(/0(08/1 2/(/0(08/1 /6(/1(08/1 04(/1(08/1 12(/1(08/1 /2(/2(08/1 00(/2(08/1 08(/2(08/1 16(/2(08/1 /3(/3(08/1 01(/3(08/1 1/(/3(08/1 17(/3(08/1 /5(/4(08/1 03(/4(08/1 11(/4(08/1 2/(/4(08/1 /6(/5(08/1 04(/5(08/1 12(/5(08/1 /0(/6(08/1 /8(/6(08/1 06(/6(08/1 14(/6(08/1 /1(/7(08/1 0/(/7(08/1 07(/7(08/1 15(/7(08/1 /2(/8(08/1 00(/8(08/1 08(/8(08/1 16(/8(08/1 /4(0/(08/1 02(0/(08/1 10(0/(08/1 18(0/(08/1 /5(/0(08/1 Figure 10 is a graphical illustration of AxisDate# Title Donkeywell Borehole MelvilleDonkeywell$" Rissington borehole ! StaPon ( $Road/RomanRiver level Way average " "Meadow !!! ViewFlooding Riverincident Level Ave Wind AMBER RED our flooding ‘trigger-level’ analysis for Bourton-on-the-Water. In Figure 10 Figure 10 Flooding ‘trigger-levels’ analysis. the brown and green lines illustrate the changing groundwater and river levels over time respectively, and the red and orange lines indicate our proposed amber and red warning ‘trigger levels’. The groundwater and river data has been plotted against the dates when the sewer network issues have occurred in the area, identified as crosses on the graph.