Hampshire County Council Flood Investigation Report

St Mary Bourne Flood Investigation

Flood Investigation Report

Document Information

Document Information Document Reference 2012-12-14/HCC/1101 Document Revision - Report Status DRAFT Author S Reghif Checked Tim Lawton – Head of Highways (West) Approved

Hampshire County Council Economy, Transport and Environment Department The Castle Winchester Hampshire SO23 8UD

Tel: 0845 603 5638 Fax: 01962 847055 www.hants.gov.uk

No part of this document may be copied or reproduced by any means without prior written permission from HCC. Any advice, opinions or recommendations within this document; a) should be read and relied upon only in the context of this document as a whole, b) do not in any way purport to include any manner of legal advice or opinion, c) are based on the information made available to HCC at the date of this document and on current UK standards, codes, technology and construction practises as at the date of this document. No liability is accepted for any use of this document other than for the purpose for which it was originally prepared and provided. Hampshire County Council cannot accept responsibility for any use or reliance on the contents from this report by any third party.

Maps are reproduced from Ordnance Survey material with the permission of Ordnance Survey on behalf of the Controller of Her Majesty’s Stationery Office © Crown Copyright. Unauthorised reproduction infringes Crown Copyright and may lead to prosecution or civil proceedings. HCC 100019180 [2011].

1 Introduction

Requirement for Investigations

Hampshire County Council (HCC), within its role as Lead Local Flood Authority, has a responsibility to record and report flood incidents, as detailed in Section 19 of Part 3 of the Flood and Water Management Act 2010.

PART 1 FLOOD AND COASTAL EROSION RISK MANAGEMENT 3. Supplemental powers and duties

Section 19: Local authorities: investigations

On becoming aware of a flood in its area, a lead local flood authority must, to the extent that it considers it necessary or appropriate, investigate –

a) which risk management authorities have relevant flood risk management functions, and b) whether each of those risk management authorities has exercised, or is proposing to exercise, those functions in response to flood.

Where an authority carries out an investigation under subsection 1) it must –

a) publish the results of its investigations; and b) notify any relevant risk management authorities.

This investigation was undertaken to look at the foul water issues in St Mary Bourne, thought to be caused by groundwater infiltration, because the impacts to people and their health were deemed significant, to trigger an investigation in line with the County Council’s guidelines.

This report aims to provide details of the incident that occurred, information on the flood history at this location as well as identifying whether each Risk Management Authority has suitably exercised its relevant functions, powers and responsibilities in their response to this incident. It also includes an overview of any works undertaken or proposed in order to mitigate against future flood risk, and makes recommendations for further works or investigations.

2 Site Location and Description The village of St Mary Bourne is located to the North East of Andover within the borough of Basingstoke and Deane as shown in Figure 1. The village is the largest within the Parish of St Mary Bourne which also includes the villages of Stoke and Binley.

Figure 1 – Location Plan

St Mary Bourne is a rural and historic area with over 70 listed buildings and the largest concentration of thatched buildings in Basingstoke & Deane borough. This area also contains a large area of agricultural land and water meadows including the Vitacress site to the south of the village.

The village is located over a chalk aquifer and as such can suffer from groundwater flooding when the water table rises under certain rainfall conditions, normally during the winter and spring months.

As can be seen in Figure 2, St Mary Bourne is located to the southern edge of the Bourne Rivulet River Catchment (as defined by the Environment Agency) and is the conduit for the majority of water from the catchment as a whole before it reaches the River Test. The Bourne Rivulet, also known as the River Swift, is a seasonal groundwater river and is classed as a ‘main river’ meaning that it falls under the Environment Agency’s remit in terms of flood risk management and responsibility.

Figure 2 – Bourne Rivulet Catchment Area

3 Incident triggering investigation In December 2012, Hampshire County Council was contacted by several residents who were unable to use washing or toilet facilities in their properties due to the foul sewer being backed up and the risk of internal foul flooding. In the opinion of these residents, this problem was not being given sufficient importance by the water company responsible for managing flooding from sewers (Southern Water). This perception was compounded by an alleged lack of communication with local residents by the water company. Although this was considered to be primarily an issue for Southern Water to deal with Hampshire County Council decided to investigate this issue in view of the

combination of different contributory flood factors and the number of different flood risk management bodies involved. The aim of this investigation was to identify what has, is and could be done to assist the residents and alleviate the risk of foul flooding.

A Hampshire County Council representative visited the site on 14 December 2012 and spoke to a number of residents about the issues as well as the Southern Water representatives who were on site dealing with the problems in the village at this time.

St Mary Bourne village was not suffering from surface water flooding at this point. There was very little ponding on the highway and no evidence of significant flooding although the surrounding fields were noticeably waterlogged.

The Bourne Rivulet was in full flow and although the actual depth was not recorded, there did not appear to be an imminent risk of it overtopping. However, the level of the water appeared to be at a very similar level to the highway which illustrates the height of the water table and corroborated the assumption that the issues were related to groundwater.

Southern Water staff were active in the village at the time of this site visit and had identified that three properties were affected.

One resident, reported that the Southern Water sewer had backfilled all of the lateral pipes, forcing them to hire a chemical toilet as no other facilities were functioning. This issue had occurred earlier in the year, for three weeks in August 2012 as well as the current incident which started on 2 December 2012 and was on-going for a considerable period. The resident had been in the property for seven years and, while aware of the potential flood risk, had never known the issues to start so early in the year.

Southern Water had arranged for tankers to remove water from the sewer at this point as well as initiating overpumping directly into the Bourne at two locations as shown on Figure 3.

It was reported that a neighbouring property was suffering the same issues, and the effects were exacerbated by the presence of young children at this property.

The third property in the line was not directly affected at that time and the occupants were able to use their bathroom facilities. However, this property is the furthest upstream of the line of three linked properties. The sewerage network links the three properties, each to the next before entering the main sewer. Therefore the problems being experienced at the most downstream of the three properties, were compounded by both of the upstream properties. It is worth noting that under new legislation, Southern Water is now responsible for sewerage pipes that serve more than one property.

Southern Water’s operational staff were on site co-ordinating the tankers and were undertaking water quality tests on the foul water to determine the level of pollutants in the system. These tests and visual inspections showed the water to be very clear and with extremely low levels of pollutants which emphasised that this was primarily a groundwater infiltration issue. This low level of pollutant meant that Southern Water were allowed to ‘overpump’ into the Bourne Rivulet without causing a detrimental affect on the watercourse and its quality. The over-pumping also included filtering out any remaining pollutants before the extracted water was released into the Bourne. The filtered out pollutant was disposed of at an approved facility to ensure the contaminates did not enter the Bourne. The water quality testing will continue for the duration of the overpumping as required by the Environment Agency.

Figure 3 – Overpumping Locations

4 History of Flooding There is a long history of flooding related problems in this area but it is widely accepted that the root cause is high groundwater levels and the infiltration of

this groundwater into the foul water sewer. Although above ground flooding has occurred, the issue causing the most concern is the inability of the foul water sewer to function effectively in periods of high groundwater.

A number of reports, surveys and investigations have been carried out and it is accepted that there is a substantial amount of groundwater entering the sewers which is preventing some properties from being able to discharge any of their foul water into the system as well as the risk of the sewer backing up into properties.

Much of the information below has been obtained from the 2005 Halcrow Report into the groundwater flooding that occurred in 2000/01, St Mary Bourne Parish Council and a local resident. Other sources of information include officers at Hampshire County Council, Basingstoke and Deane Borough Council, the Environment Agency and Southern Water.

The Halcrow report identified that flooding was experienced in St Mary Bourne in 1960, 1980, 1995 and 2000/01. No information is readily available from the earlier events but the Halcrow report identified that the 1995 event was very similar to that experienced in 2000/01. This Halcrow report is appended to this document.

The flooding in 2000/01 was the result of high ground water levels following a period of exceptionally high rainfall which led to high water levels in the Bourne Rivulet. The water levels were reported to have caused the foul sewerage systems to become surcharged which led to a number of properties being flooded internally by foul water as well as others being unable to discharge their foul water into the sewer.

In addition to this, there was considerable surface water flooding as a result of the Bourne Rivulet overtopping and water being unable to drain away.

During this period, Southern Water employed tankering and overpumping to alleviate the issue and it has been documented that tankering was required every year between 1995 and 2001. Following this incident, Southern Water undertook CCTV surveys of the main foul sewer, including laterals, and in conjunction with Basingstoke and Deane Borough and St Mary Bourne Parish Councils, carried out re-lining works in a number of locations. This report identified a number of leaking laterals within and outside of St Mary Bourne village.

Officer reports have identified that between 2003 and 2008 work was carried out to seal some leaking laterals on several occasions by the different agencies but it is not clear how many were repaired or whether the repairs were successful.

In 2010, Southern Water installed small pumping stations and underground tanks for two properties which allowed the foul water to be released into the sewer in times of low flow. Although this seems to have alleviated the issue

for these properties, it would seem that the problem has simply moved further upstream and other properties are now being affected.

5 Summary of Roles, Responsibilities and Actions

Due to the complexity and variety of the different roles and responsibilities, only a brief summary of each organisation’s role with respect to this flood incident has been listed together with a summary of the actions taken prior to and during this incident.

Additional information on the roles and responsibilities for each organisation can be found within Appendix C1 of the Local Flood Risk Management Strategy produced by Hampshire County Council. This document can be found at http://www3.hants.gov.uk/flooding/floodriskstrategy/floodriskstrategy- consultation.htm

5.1 Hampshire County Council Hampshire County Council has two main roles: Lead Local Flood Authority (LLFA) and Highway Authority.

As a Highway Authority, Hampshire County Council has a responsibility to manage the highway drainage, ensuring it is fit for purpose. On 30 November 2012 and 3 January 2013, the highway drainage network was checked and cleaned to ensure it was functioning correctly. It was noted at this time that none of the drainage entered into the sewerage system and fed directly to the Bourne.

As LLFA, Hampshire County Council is responsible for taking the lead in co- ordinating the management of local flood risk (including groundwater) and as such, initiated a meeting of all relevant authorities to determine what was being done to manage this incident. The initial meeting took place on 20 December 12, with regular meetings having taken place since. The meetings have taken the form of the St Mary Bourne Technical Steering Group comprising representatives of not only Southern Water, the Environment Agency and the County Council but also Basingstoke & Deane Borough Council, Test Valley Borough Council and St Mary Bourne Parish Council. The terms of reference of this Technical Steering Group are appended to this report. The main output of the group will be a draft Infiltration Reduction Plan for St Mary Bourne, agreed by all parties, with outcomes including increased partnership working and improved communications with local residents.

5.2 Southern Water As a Sewerage Authority, Southern Water is responsible for the effective draining of foul water and roof and yard runoff from properties. The longstanding issues have highlighted that the current foul system is incapable of draining foul water effectively during times of high groundwater and, despite the considerable amount of money spent on the relining of main

sewers and ancillary works, this had not, at the time of the investigation, resolved the issue.

Recent changes in legislation mean that Southern Water is also responsible for sewer connections once they leave the boundary of a property. Within the property boundary the sewer connection remains the property owner’s responsibility. The exception to this is where multiple properties are linked to sewer connections. Where this is the case, Southern Water is responsible for the connection despite being within the property boundary (see also Section 3 above).

Southern Water has plans in place which facilitate the need tankering and overpumping into the Bourne when the groundwater levels prevent the sewer from functioning correctly. Both of these activities were being undertaken in accordance with Southern Water’s emergency response plan. In response to the most recent incident Southern Water commenced preparation of an Infiltration Reduction Plan

5.3 Environment Agency As the responsible organisation for managing flood risk from main rivers and the sea, the Environment Agency issue warnings or in this case, Groundwater Alerts when the levels in these features reach a certain level. However, since the Bourne Rivulet has not overtopped, there is little more that can be done at this time.

The Environment Agency is also responsible for monitoring river water quality, controlling discharges into watercourses and dealing with pollution incidents. The overpumping is classed as a pollution incident and the Environment Agency is ensuring that the water quality in the Bourne is not compromised.

A new duty for the Environment Agency is the approval of ‘Infiltration Reduction Plans’ (IRP) which is a new approach to assess and mitigate infiltration issues in a formal and comprehensive manner. Southern Water is preparing an IRP, and will submit it to Environment Agency for approval. The St Mary Bourne Technical Steering Group will input into the preparation of this Plan.

5.4 Basingstoke and Deane Borough The Borough Council has Environmental Health and Building Control responsibilities which come with permissive powers in relation to land drainage. The Borough Council’s Environmental Health team can take action to investigate and resolve problems with spillage, overflow or odour affecting septic tanks and cesspools.

Prior to this incident, the Borough Council has assisted in carrying out CCTV surveys of lateral connections and provided assistance to property owners in repairing leaking laterals. However, no action had been taken in relation to this incident.

5.5 St Mary Bourne Parish Parish Councils do not have formal Flood Risk Management responsibilities. However they can play an important role in liaising with the public and risk management authorities. This has been the case prior to and during this incident where the Parish Council has been a key facilitator of contact and liaison with the different agencies and providing information for local residents.

5.6 Residents Residents and homeowners have the responsibility to ensure that they are aware of any flood risk which may affect them and that they take appropriate steps to ensure that their properties are protected to a suitable standard. In relation to this incident, this means that they should ensure that the foul water laterals which serve only their property and are within the property boundary, are of a suitable standard and in a suitable state of repair. Although it has been identified that some of these laterals require repair, it is not clear which ones are substandard.

6 Next Steps Hampshire County Council has taken the lead in bringing the relevant agencies together to, in the first instance, ensure that all that could reasonably be done in response to this incident, was done. Southern Water was also encouraged to take the lead in putting together a plan to reduce the amount of ground water inundation into the sewerage network and to resolve the problems being experienced by local residents..

Multi-agency meetings were held and are still being held to identify and discuss the issues, assess proposed mitigation measures and co-ordinate the communication of this information to other parties including local residents.

Southern Water is producing a draft Infiltration Reduction Plan to develop a programme of investigation and works to reduce the risk and impact of groundwater flooding. This plan will be formally signed off by the Environment Agency and published in due course.

As part of the evidence-gathering under-pinning the preparation of the draft IRP, a comprehensive programme of CCTV has been undertaken to identify the source or sources of the infiltration. This has identified a number of issues some of which have already been resolved and others which are programmed for works at a later date. Where infiltration is as a result of 3rd party apparatus, Southern Water is in discussion with the property owners to determine the most appropriate way to prevent that infiltration.

Southern Water will continue to release regular updates to all residents and interested parties to ensure the community are aware of the plans and proposals.

7 Conclusion This report has shown that the cause of this incident is known and understood.

Although above ground flooding is not causing significant issues, the overloading of the foul sewer is causing considerable distress to a number of residents within the village, particularly given the length of time that these issues have been occurring and the perceived lack of progress. There is also local concern at potential environmental harm through the over pumping into the Bourne

Although properties and residents suffered from the overloaded sewer and disturbance from tankering, there is little else that could have been done in the short term while the groundwater levels were high. However, there is a considerable amount of background information on these issues, both historic and from the CCTV survey, which should allow the IRP being drawn up by Southern Water to identify what can be done.

The Environment Agency has monitored the overpumping and sampling has assured that water quality remains well within acceptable levels. Given that overpumping is considered as a pollution incident, they are overseeing the production of the Infiltration Reduction Plan to reduce the risk of this being required in future years.

As the Local Highway Authority, Hampshire County Council has checked the Highway drainage and confirmed that this does not interact with the sewer network and does not have an impact on sewer infiltration in this area.

Southern Water has worked with all parties to control the impact of the sewer infiltration as well as developing mitigation measures through the emerging Infiltration Reduction Plan. This document will be within the public domain once approved and will inform Southern Water’s maintenance and repair programme. Southern Water is providing regular updates to the community and ensuring that all parties are kept informed of the progress made.

Hampshire County Council as LLFA has ensured that relevant parties are aware of their statutory duties and responsibilities and that each party is acting in accordance with those duties. There is an undertaking to continue with the multi-agency approach by all parties to deal with Groundwater flooding and sewer infiltration issues in St Mary Bourne and the surrounding areas until such time that the risk is reduced to acceptable levels.

All parties have learned a great deal from working together to address the problems described in this report and it is being taken forward by the Environment Agency and Southern Water as a model for addressing similar problems elsewhere in the County and beyond.

Following notification of this incident and as a result of the regular multi- agency meetings held, Hampshire County Council is satisfied that Southern

Water, and all other Risk management Authorities, have fulfilled their requirements under the Flood and Water Management Act.

Useful Contacts

Environment Agency General Enquiries 08708 506 506 (Mon-Fri, 8am - 6pm) Incident Hotline 0800 80 70 60 (24 hrs)

Basingstoke and Deane Borough Council General Enquiries 01256 844844

Hampshire County Council Emergency Planning Unit 01962 846846 [email protected]

Hampshire County Council Contact Centre 0845 603 5633

Report Road Problems Online Service: http://www3.hants.gov.uk/index/transport/roadproblems.htm

Lead Local Flood Authority www.hants.gov.uk/flooding

Southern Water

Links

Highways Act 1980: http://www.legislation.gov.uk/ukpga/1980/66/contents

Flood and Water Management Act 2010: http://www.legislation.gov.uk/ukpga/2010/29/contents

Land Drainage Act 1991: http://www.legislation.gov.uk/ukpga/1991/59/contents

Environment Agency – River and Coastal Maintenance Programmes: http://www.environment-agency.gov.uk/homeandleisure/floods/109548.aspx

Environment Agency – Prepare your Property for Flooding: http://www.environment-agency.gov.uk/homeandleisure/floods/31644.aspx

St Mary Bourne Drainage Technical Steering Group

Appendix St Mary Bourne Drainage Technical Steering Group

Terms of Reference

OBJECTIVES During periods of high groundwater the foul sewerage system in and upstream of St Mary Bourne, Hampshire, experiences inflows which cause it to become hydraulically overloaded. This leads to the pollution of local watercourses, unusable sanitation and foul flooding in the villages of St. Mary Bourne and Stoke. The objectives of the group, insofar as it is legally, technically, economically, environmentally and socially feasible, are: 1) to understand the nature and location of these inflows; 2) to reduce them to an acceptable level; and 3) to establish measures to ensure that they remain at an acceptable level in the future.

CONSTITUTION The group will comprise the following organisations:  Hampshire County Council, (Lead Local Flood Authority and Highway Authority)  The Environment Agency  Southern Water  Basingstoke & Deane Borough Council  Test Valley District Council  St Mary Bourne Parish Council

Meetings will be held monthly or at a frequency agreed by the group. Meetings will normally comprise one representative from each organisation. However, it may be necessary for other specialists and advisors to attend from time to time. Agendas will be prepared by Hampshire County Council in consultation with group members. Meetings will be chaired by Hampshire County Council as Lead Local Flood Authority. Minutes will be taken at all meetings and distributed by Hampshire County Council. The responsibility for agreed actions and their target dates will be included in the minutes.

METHODOLOGY The objectives of the group will be approached as follows:  A long term infiltration reduction plan will be agreed and maintained. The level of detail in this plan is likely to increase as investigations are carried out and a better understanding is gained of the sources of inflow. The plan will be prepared and maintained by Southern Water by agreement with the group and copies of all updates will be distributed to the group.  Inflows will be addressed on the basis of their magnitude irrespective of their nature and location.

 Responsibility for actions and target dates will be included in the plan and all organisations will assist and support one another in carrying out these actions.  The residents of St Mary Bourne and Stoke will be consulted for their understanding of the problem and their agreement to the plan and will be provided with feedback on the progress of the plan. The method of consultation and feedback will be agreed by the group.  Releases to the press and general public will only be made with the agreement of all members of the group.  Data will be shared by the group on a reciprocal and best endeavours basis. However, in recognition of the potential impact of publication of this data on the interests of the residents and group members, sharing will be subject to the terms of a formal protocol agreed by the group.