Section 19 Investigation Report Metropolitan Borough Council

June 2016 Flood Events

D01 | V01 October 2016 131251

June 2016 Fl ood Events Stockport Metr opolitan Borough Council

June 2016 Flood Events

Section 19 Investigation Report

Project No: B2278700 Document Title: June 2016 Flood Events Document No.: D01 Revision: V01 Date: October 2016 Client Name: Stockport Metropolitan Borough Council Client No: 131251 Project Manager: Chris Isherwood Author: Tim Diesner File Name: 2016-10-19_B2278700_S19InvestigationReport_D01.docx

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Document history and status

Revision Date Description By Review Approved

D01 19/10/2016 Draft report issued to client for comment T Diesner C Isherwood C Isherwood

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Contents 1. Introduction ...... 1 1.1 Summary of Events ...... 1 1.2 Purpose & Scope of this Report ...... 1 1.3 Legislative Background ...... 1 1.4 Risk Management Authorities ...... 2 2. Overview of Flooding Events ...... 4 2.1 Property Impacts ...... 4 2.2 Conditions during June 2016 ...... 5 2.3 EA Flood Alerts ...... 8 3. ...... 9 3.1 Site Overview & Flooding Impacts ...... 9 3.2 Flooding Analysis ...... 9 3.3 RMA Responses ...... 12 3.4 Recommended Actions ...... 13 4. Hazel Grove ...... 14 4.1 Site Overview & Flooding Impacts ...... 14 4.2 Flooding Analysis ...... 15 4.3 RMA Responses ...... 17 4.4 Recommended Actions ...... 18 5. Offerton Green ...... 19 5.1 Site Overview & Flooding Impacts ...... 19 5.2 Flooding Analysis ...... 20 5.3 RMA Responses ...... 22 5.4 Recommended Actions ...... 23 6. Edgeley ...... 24 6.1 Site Overview & Flooding Impacts ...... 24 6.2 Flooding Analysis ...... 24 6.3 RMA Responses ...... 26 6.4 Recommended Actions ...... 26 7. Other Incidents ...... 27 7.1 High Lane ...... 27 7.2 Infrastructure Impacts ...... 27 8. Conclusion ...... 28

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1. Introduction

1.1 Summary of Events

Localised flooding occurred across many areas of Stockport during June 2016 following periods of heavy downpours. As a result, numerous properties suffered internal and external flooding, many roads became impassable and were closed, and a landslip caused significant disruption to the local railway network.

Three key flooding events have been identified and took place on:  8 June 2016 – impacting Offerton Green  11 June 2016 – impacting Bramhall, Hazel Grove, Offerton Green, High Lane  16 June 2016 – impacting Edgeley

High river levels and overwhelmed surface water drainage systems as a result of prolonged and heavy rainfall saw the flooding of 141 properties across Stockport on 11 June, 86 of which suffered internal flooding. Heavy rainfall also overwhelmed local drainage systems on both 8 June and 16 June, however, the flooding impacts were much less severe with 17 properties on 8 June and 3 properties on 16 June suffered internal flooding.

1.2 Purpose & Scope of this Report

Given that the flooding events across June 2016 affected a large number of residential properties and critical infrastructure such as rail links, bridges and ‘A’ roads, it is classified as a ‘significant’ event under Stockport’s Local Flood Risk Management Strategy (LFRMS)1 and therefore a full investigation is required.

The aim of this investigation is to identify all the communities that were affected by the June 2016 flooding events and to determine the source, cause and impact of the events (in accordance with Section 19 of the Flood and Water Management Act 2010 (the Act)).

The study will also seek to investigate certain issues of local concern regarding flood risk, such as the impact of development outside of Stockport on flood risk within the borough and the impact of the A6 to Manchester Airport Relief Road (A6MARR), which is currently under construction. Recommendations arising from the investigation will be made to Stockport Metropolitan Borough Council (SMBC) and the other Risk Management Authorities (RMAs) within the borough.

1.3 Legislative Background

1.3.1 Section 19 Investigations

The Act places a number of duties on Lead Local Flood Authorities (LLFAs) in relation to local flood risk management. One of the principal duties of the LLFAs, as laid out in the Act, is the responsibility to record and investigate flooding incidents within their area (known as Section 19 Investigations).

Section 19 of the Act states: 1) 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 the flood. 2) Where an authority carries out an investigation under subsection (1) it must -

1 Local Flood Risk Management Strategy for Stockport (2016). Available online at http://www.stockport.gov.uk/2013/3006/540775/lfrm

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a) Publish the results of its investigation, and b) Notify any relevant risk management authorities.

1.3.2 Stockport Local Flood Risk Management Strategy

The LFRMS for Stockport sets out how SMBC intends to manage risk from local sources of flooding. This includes how the Council will implement the number of legal duties and responsibilities placed upon them under the Act, including the duty to investigate and report on flooding incidents that occur in their area.

The LFRMS states that flood events within Stockport must be recorded and investigated according to the procedures set out in the Association of Authorities (AGMA) policy document “Recording and Investigation of Flood Events”. This policy requires that a full investigation is carried out if a flooding event is deemed to be a ‘significant’ incident.

Based on the number of properties which suffered internal flooding and the impact on critical infrastructure (e.g. A roads, rail links, bridges), the flooding events in Stockport of June 2016 are classified as ‘significant’ under local policy and require a full investigation.

1.4 Risk Management Authorities

The Following organisations are defined as RMAs under the Act and have the following flood risk management functions. Table 1.1 lists each RMA and the source of flooding in which they are responsible for.

Table 1.1 : RMAs within Stockport and their areas of responsibility

Highway Lead Local Water District Authority Environment Flood Companies Flood Source Council (SMBC & Agency Authority (United Highways (SMBC) (SMBC) Utilities) ) Main River*  Ordinary Watercourse*  

Surface water from  highway

Surface water from other  sources Sewer flooding  The Sea 

Groundwater flooding  Water supply  infrastructure

*Main Rivers have been designated as such by the Environment Agency. These tend to be major rivers or rivers with a high flood risk. Ordinary watercourses are all other rivers and streams not classified as main rivers.

1.4.1 Environment Agency

The Environment Agency (EA) has a strategic overview of all sources of flooding and coastal erosion (as defined in the Act). It is also responsible for flood and coastal erosion risk management activities on main rivers and the coast, regulating reservoir safety, and working in partnership with the Met Office to provide flood forecasts and warnings.

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1.4.2 Stockport Metropolitan Borough Council SMBC has a joint risk management role in its capacity as district council, highway authority and LLFA. The Council as a highway authority has a duty under the Highways Act 1980 to maintain highways that are maintainable at public expense. This requires attention to the drainage requirements of the public highway. As LLFA, SMBC has a number of duties and powers as laid out under the Act, in addition to the duty to investigate flooding set out above. The LFRMS describes these in more detail. SMBC also take an overseeing role to ensure that RMAs and landowners are fulfilling their responsibilities adequately.

1.4.3 Highways England

Highways England has responsibility as a highway authority for the motorways in Stockport. It shares the same duties to flood risk management as SMBC as a highway authority.

1.4.4 Water Companies

Water companies have a duty under Section 94 of the Water Industry Act 1991 to provide and maintain sewers for the drainage of buildings and associated paved areas within property boundaries. They are also now responsible for private sewers and lateral drains, which communicate with the public sewers.

United Utilities (UU) are the local water company within the borough of Stockport. With regards to local flood risk management, they are responsible for any flooding which is directly caused by its assets – i.e. its water or sewerage pipes, and must maintain a register of properties that have flooded due to hydraulic incapacity of the sewerage network, and have a duty to cooperate with other relevant authorities.

1.4.5 Other Stakeholders

Riparian landowners are those who own land adjoining or containing a watercourse. They have certain rights and responsibilities, including the maintenance of watercourses and assets within their ownership to ensure flood risks are not increased upstream or downstream of their land.

Residents who are concerned they may be at risk of flooding should take appropriate action to protect themselves and their property. These actions include registering to receive flood warnings, obtaining a personal supply of sandbags, and moving valuable items to higher ground. They also include more resilient and permanent property protection measures including water resistant doors, air brick covers, floodgates, raised electrical sockets and the fitting of non-return valves on pipes.

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2. Overview of Flooding Events

2.1 Property Impacts

Three storm events occurred during the month of June 2016, which resulted in property flooding within Stockport. The most significant flooding event occurred on 11 June; 141 properties across Stockport were reported to be affected by flooding, of which 86 properties suffering internal flooding. Other storm events occurred on 8 June and 16 June, but caused a much lower degree of flooding.

This report will focus primarily on the flooding event of the 11 June, which affected not only properties but also local infrastructure and required a significant response from the local emergency services and local council.

Four areas within Stockport suffered property flooding during this event: 1) Offerton Green; 2) Hazel Grove; 3) Bramhall; and 4) High Lane.

Figure 2.1 identifies the general location and the scale of property flooding in Stockport on the 11 June.

Figure 2.1 : Location of property flooding on 11 June 2016

Table 2.1 provides the number of properties flooded by location within Stockport on 11 June 2016; this shows that Offerton Green and Hazel Grove were the areas most affected, Bramhall suffered to a lesser degree and

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High Lane suffered relatively little impacts. These numbers were confirmed by the EA following the event by questioning residents door-to-door; however the numbers may be higher given locations where residents were unavailable or flooding was not reported.

Property flooding also occurred on 8 June in Offerton Green and on 16 June in Edgeley but to a much lesser degree. The flooding impacts through the month of June 2016 and the causes of flooding are investigated further in the following sections of the report on a site-by-site basis. The following sub-section of the report, Section 2.2, provides an analysis of the conditions that may have led to the flooding during June 2016.

Table 2.1 : EA confirmed property flooding on 11 June 2016

Location Number of properties Number of properties only Total number of properties internally flooded externally flooded affected

Offerton Green 65 2 67 Hazel Grove 9 43 52 Bramhall 12 6 18 High Lane 0 4 4 Total 86 55 141

The locations of individual properties reported to have flooded during June 2016 event have not been identified in this report for reasons of confidentiality; instead, the total number of properties affected are provided on a road-by-road basis.

2.2 Conditions during June 2016

2.2.1 Overview

The following information has been used to help provide an overall picture of the conditions that led to the flooding events in Stockport over June 2016:  EA Water Situation Reports - The EA issues monthly water situation reports for England2, which provide an overview of various hydrological information including rainfall, soil moisture and river flows for the month.  CEH Hydrological Summary reports – The Centre for Ecology and Hydrology (CEH) issues reports for the United Kingdom3, which, similar to the EA Water Situation Reports, provide analysis of various hydrological records for the month.

The CEH states that the first week of June 2016 was dry and settled, but showers and storms dominated the rest of the month, bringing substantial rainfall. According to CEH gridded rainfall data for the UK, the June 2016 rainfall in Stockport was equal to or above 200% of the 1971 to 2000 long-term average rainfall.

The Soil Moisture Deficit (SMD) is a measure of how saturated the ground is; low values reflect more saturated ground conditions, high values reflect less saturated ground conditions. The EA Water Situation Reports provide a measure of SMD on a 40 x 40 km grid of the UK. For the grid square that the Stockport borough falls within, the SMD was below the 1961 to 1990 long term average at the end of May 2016 (by 25 to 6 mm) and even further below the long term average at the end of June 2016 (by 50 to 26 mm). The EA also classes the absolute value of the SMD in seven bands as a relative indication of soil moisture. The SMD fell from the second lowest band (11 to 40 mm) to the lowest band (<=10 mm) from the end of May to the end of June 2016.

In summary, the available data indicates that the ground conditions were heavily saturated and more saturated than average in June 2016 in the Stockport area. These saturated ground conditions mean that more surface

2 https://www.gov.uk/government/collections/water-situation-reports-for-england 3 http://nrfa.ceh.ac.uk/monthly-hydrological-summary-uk

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water runoff than typical for the time of year would have been generated for any given rainfall event, with a greater potential for rapid surface water flooding and prompt increases in river levels.

2.2.2 Rainfall Records

One EA rain gauge is located within the Stockport borough at Meadowbank School in Cheadle, shown in Figure 2.2. The rain gauge is a tipping bucket rain gauge recording at 15 minute intervals. Figure 2.3 presents the daily rainfall totals recorded during the month of June 2016.

Figure 2.2 : Meadowbank School rain gauge location

The graph shows that no rainfall was recorded at the gauge at the start of the month, and that the rain started on 07 June and built to a peak on 11 June. Following 11 June, rainfall is shown generally to decrease day on day until 16 June, which is shown to be a standalone day of heavy rainfall. The total daily rainfall recorded on 16 June at the gauge exceeded that of 11 June. Rain is shown to fall on most days during the rest of the month, but the daily rainfall totals generally don’t exceed those recorded in the first half of the month.

Four days of increasing amounts of rainfall leading to 11 June would suggest that the ground conditions in Stockport could have been quite saturated before the flooding incident on 11 June, meaning a lot of the rain that fell on 11 June was converted into runoff and entered into the local watercourses.

More rainfall was recorded on 16 June than any other day during the month, yet only six properties in Edgeley were flooded on this day; this highlights the spatial variation of rainfall, that whilst Meadowbank School at Cheadle and also Edgeley may have received significant amounts of rainfall, other areas of Stockport did not. This could also indicate that the duration over which rain fell on each day was important to the flooding that occurred.

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Figure 2.3 : Daily rainfall totals recorded during June 2016 at Meadowbank School rain gauge

Closer inspection of the detailed rainfall record on the key flooding dates of 8, 11 and 16 June shows that:  On 8 June, the rainfall was high in intensity and short in duration: the rainfall event began at 15:00 and ended at 16:30, with a peak intensity of 20 mm/hr.  On 11 June, the rainfall was lower in intensity but much longer in duration: the rainfall event began at 10:00 and ended at 18:00, with a peak intensity of 11 mm/hr.  On 16 June, the rainfall was very high in intensity and short in duration: the rainfall event began at 17:00 and ended at 19:15, with a peak intensity of 38 mm/hr.

Without analysing the sources of flooding that occurred on these dates, from these conditions one might expect:  Predominantly surface water flooding on 8 June: urban drainage systems are often overwhelmed by short duration and high intensity rainfall events.  Predominantly fluvial flooding on 11 June: water levels on rivers often take a while to respond to rainfall falling on the river catchment, a lower intensity but longer period of rainfall would allow river levels to build. Urban drainage systems are better at coping with lower intensity rainfall.  Predominantly surface water flooding on 16 June: urban drainage systems are often overwhelmed by short duration and high intensity rainfall events.

The EA also provided radar imaging of the storms on 8 June and 11 June for use in this study. Whilst these images help provide an understanding of where and when the storms were most intense, they do not necessarily provide a good overall picture of the event and as such have not been used in this section of the report. These images are used in the site specific analysis of the flooding events in the following sections of the report.

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2.2.3 River Level Records

Of the river catchments where fluvial flooding occurred during June 2016 in Stockport, Poise Brook is the only gauged watercourse for which a record is available for the event. This gauge is located on the outlet debris screen of the reservoir on Poise Brook at head of Cooper Street in Hazel Grove, and is primarily used by the EA to determine if the screen requires clearing of debris, but also is also used to provide Flood Warnings to properties located in vulnerable areas along this watercourse.

During the month of June 2016 the station record shows a clear peak on 11 June followed by slightly elevated levels on 12 June. The gauging station became operational during October 2014 and consequently the historic record is short, however the peak level recorded on 11 June 2016 was the highest level recorded in the station’s history. A peak level of 2.04 m was recorded on 11 June; the average level recorded in this period was approximately 0.06 m.

Further analysis of the impacts of raised levels on Poise Brook is made with respect to the flooding in the Hazel Grove and Offerton Green areas in the following sections of the report.

2.3 EA Flood Alerts

The EA use three flood warning codes depending on the severity of flooding expected (see Table 2.2); these are also issued at different intervals in advance of flooding. Flood Alert areas generally cover a large area, whilst Flood Warning areas are usually more detailed and broken down into specific locations. Locations within a Flood Alert area are also not necessarily within a Flood Warning area.

Flood Alerts, but no Flood Warnings, were issued at key locations of flooding during the June 2016 flood events in Stockport. Further detail regarding the alerts issued at the key flooding locations is provided within the following sections of the report.

Table 2.2 : EA Flood Warning Codes

Flood warning codes What it means When it’s used

Flood Alert Flooding is possible. Be prepared. Two hours to two days in advance of flooding. Flood Warning Flooding is expected. Immediate Half an hour to one day in advance action required. of flooding. Severe Flood Warning Severe flooding. Danger to life. When flooding poses a significant threat to life.

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3. Bramhall

3.1 Site Overview & Flooding Impacts

Bramhall is a suburb of Stockport and is located between to the west and Hazel Grove to the east. Lady Brook is an EA main river, which flows from east to west through the area; there are also several smaller tributaries of Lady Brook that drain through the area.

A total of 18 properties located on Bridge Lane (residential and commercial) suffered flooding on 11 June 2016, of which 12 properties suffered internal flooding. The Bramhall roundabout and Bridge Lane were flooded and subsequently closed to traffic. The flooding led to the evacuation of some of the local residents.

Figure 3.1 : Bramhall site overview

3.2 Flooding Analysis

It is reported that Bridge Lane on 11 June was flooded by a combination of surface water flooding, sewer flooding and fluvial flooding. In the early to late afternoon, heavy rainfall resulted in the surface water sewers on Bridge Lane becoming overwhelmed; consequently rainfall pooled on Bridge Lane and at the Bramhall Roundabout, encroaching on the front of the properties. Residents also reported water flooding out of the local drains. In the early evening steadily rising levels on Lady Brook then overtopped into the rear of the properties on Bridge Lane and flooded towards the road.

The rainfall radar snapshot at 14:00 on 11 June, presented in Figure 3.2, would indicate that the Bridge Lane area of Bramhall received some intense rainfall during the day (at least, for a period). It is understood that the volume of rainfall overwhelmed many of the highway drains in the Bramhall area, and it is understood that runoff flowed along Bramhall Lane South and contributed to the flooding on Bridge Lane. The EA surface water flood

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maps confirm that surface water runoff from certain areas to the south of Bridge Lane naturally drain towards Bridge Lane via Bramhall Lane South.

Figure 3.2 : Radar rainfall intensities at 14:00 on 11 June 2016 at Bramhall

Bramhall – Bridge Lane

(Source: Environment Agency)

Comparing the catchment of Lady Brook (in the left of Figure 3.2) with the rainfall radar snapshot (to the right), it can be seen that a significant proportion of the catchment was located within the most intense part of the storm and a significant amount of rain would have fallen on the catchment of Lady Brook.

Given that the ground conditions were already highly saturated before the storm hit, it is likely that a significant proportion of the rain that fell on the Lady Brook catchment would have been converted into runoff. Based on the Meadowbank School rain gauge record (Section 2.2.2); the storm on 11 June lasted for approximately eight hours. This means that runoff into Lady Brook would have been generated over a long period, allowing the water levels to climb.

No water level gauges are located on Lady Brook, but based on reports of the flooding it took approximately 4 to 4.5 hours from the time of the rainfall radar snapshot above for water levels to rise significantly enough in Lady Brook to overtop the banks at Bridge Lane. A Flood Alert was issued by the EA for this area at 19:42 on 11 June; river flooding had already occurred by this time.

Analysis of the local topography shows that Bridge Lane is low-lying when compared to the surrounding area, which would explain why it is more prone to flooding from the river. There are two single span access bridges which cross Lady Brook between Bramhall Bridge and the Bridge Lane crossing; it is understood that these bridges did not block during the flood event. Because water levels rose above the soffit level at the upstream face of Bramhall Bridge it is possible that this structure may be the key control on water levels in this reach of the river. The EA are in the process of developing a detailed hydraulic model of Lady Brook to better understand the flooding mechanisms; the results should show what impact the bridge has on flooding along this reach.

The flooding on 11 June 2016 in the Bridge Lane area of Bramhall was not unprecedented. The BBC’s Domesday Project (1986) has an entry regarding flooding in Bramhall in July 19734; this entry records that Bridge Lane is prone to flooding, and in July 1973 a violent thunderstorm resulted in spilling from the drainage

4 Domesday Reloaded, 1986 ‘The Flood’ http://www.bbc.co.uk/history/domesday/dblock/GB-388000-384000/page/19 (Accessed 22/08/2016)

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sewers and Lady Brook bursting its banks in places. Shops and houses were reportedly under water to a depth of three feet. The Manchester Evening News5 also reports that Lady Brook flooded the gardens of properties on Bridge Lane more recently, in April 2010.

Figure 3.3 : Lady Brook flood flow routes

Regarding the impact of new development within the area on local flood risk, construction of the A6 Manchester Airport Relief Road (A6MARR) was ongoing at the time of the June 2016 flooding events. The scheme follows a route adjacent to Norbury Brook and crosses Lady Brook near Norbury Moor; however, the scheme in construction is considered to have had a negligible impact on the flood risk at Bramhall from Lady Brook.

Earthworks for this section of the new road were being undertaken during June 2016 and are unlikely to have contributed a significantly greater volume or rate of runoff to either Norbury Brook or Lady Brook compared to a pre-construction case. The area being developed for the road is small in relation to the total catchment area of Lady Brook.

It is also worth highlighting that as a planning condition the completed highway must not increase the runoff received by any of the local watercourses; the road drainage systems must mimic the existing drainage mechanisms of the area developed. As such, local flood risk should not be increased as a result of this scheme.

It is also noted that the majority of the catchment area of Lady Brook lies beyond the Stockport borough within Poynton. Similar to development of the A6MARR, national planning policy requires that new development must not increase the flood risk beyond the development site, and as such there should be no recent development outside of Stockport borough that has impacted the flood risk within Stockport.

5 MEN article from 19/04/2010 - http://www.manchestereveningnews.co.uk/news/local-news/flooding-misery---and-theres-more-966675 (accessed 22/08/2016)

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Over 5 km of the Macclesfield Canal passes through the catchment of Lady Brook; it is not understood how the canal responded to the 11 June storm event, nor if overflows or discharges from the canal contributed to the flows on Lady Brook.

3.3 RMA Responses

The following information has been collected regarding the RMA responses both during and following the 11 June 2016 flooding event in Bramhall. The lists are not necessarily comprehensive and may not cover all actions taken by the RMAs.

During the flooding event:  Solutions SK (SMBC’s environmental services provider) carried out road closures of Bridge Lane and the Bramhall roundabout during the event at the request of the police and put in place diversions.  SMBC delivered sandbags to Bridge Lane and Carrwood Road (period 17:00 on 11 June to 01:30 on 12 June).  SMBC established an evacuation centre at Hazel Grove Life Centre (later closed as all residents who evacuated had accommodation).  The Bridge Lane area in Bramhall is located within the Middle River Mersey catchment Flood Alert Area. A Flood Alert was issued at 19:42 on 11 June and cancelled at 08:44 on 16 June. Flood Warnings are not issued for this area. Following the flooding event:  SMBC clean-up operation (including highway surface and drainage clearance).  SMBC provided skips for residents’ clean-up.  SMBC site inspection at Bramhall Park, Bramhall roundabout and along Lady Brook.  SMBC liaised with EA and UU with respect to flooding.  SMBC commissioned this S19 report.  SMBC engineer inspected Bramhall Bridge and confirmed safe to re-open.  SMBC set up a Recovery Coordination Group which helped support affected residents and businesses.  UU surveyed the local sewer network but found no evidence of any blockages within the system that could have contributed to the flooding.  EA door-to-door survey of flood impacts.

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3.4 Recommended Actions

Based on the analysis of the June 2016 flooding events in Hazel Grove, the following actions are recommended to the local RMAs:

Table 3.1 : Recommended actions for Bramhall

RMA Recommended Action

SMBC Highways Department Maintain efficient operation of highway drains. SMBC as LLFA Consider provision of Property Level Protection for properties at risk Maintain efficient operation of surface water and combined sewers

United Utilities Review capacity of local surface water sewers (particularly with respect to sewer flooding on Bridge Lane) and consider options to reduce risk of sewer flooding Review borough-wide flood management and consider options to reduce fluvial flood risk on Lady Brook. Environment Agency Ensure watercourses are suitably maintained Review trigger levels for Flood Alerts in this area Property Owners Consider installation of Property Level Protection SMBC as LLFA Continue to manage flood risk from new development. Seek flood risk Environment Agency benefits from new development where possible.

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4. Hazel Grove

4.1 Site Overview & Flooding Impacts

Hazel Grove is a suburb of Stockport and is located between Norbury Moor to the south and Offerton Green to the north. Hazel Grove Brook, an EA main river, flows in a northerly direction through Torkington Park and Hazel Grove. It becomes Poise Brook downstream of Bosdenfold Road, where it receives flow from the Poise Brook reservoir located at the head of Cooper Street. For clarity, Hazel Grove Brook is often referred to as Poise Brook through this part of Hazel Grove; this report uses the EA naming conventions for the local watercourses – this is less misleading when referring to river gauge locations.

Offerton Green is located approximately 500 m downstream of Hazel Grove on Poise Brook; the flooding here is discussed in Section 5 of the report.

A total of 52 residential properties were reported to suffer flooding in Hazel Grove on 11 June; the majority of this flooding was only to the outside of properties and caused no internal damage. External flooding was reported at 23 properties on Nelson Street, at 15 properties on Hazelwood Road and at five properties on Wellington Street. Internal property flooding was suffered by two properties on Torkington Road, five properties on Hazelwood Road and two properties on Kintore Avenue.

Torkington Park was also flooded and both Torkington Road and Hazelwood Road were closed to traffic as a result of flooding on the highway.

Figure 4.1 : Hazel Grove site overview

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4.2 Flooding Analysis

The rainfall radar snapshot at 14:00 on 11 June, presented in Figure 4.2, shows that Hazel Grove was located within a large area of extremely intense rainfall within the storm. Reports suggest that by and large Hazel Grove was not significantly impacted by the amount of rain that fell on the area during the storm event. The exception to this is Kintore Avenue, where the highway flooded and water is reported to have entered two properties. EA surface water flood mapping indicates that Kintore Avenue would suffer highway flooding in an extreme storm event.

Figure 4.2 : Radar rainfall intensities at 14:00 on 11 June 2016 at Hazel Grove

Hazel Grove

(Source: Environment Agency)

Whilst the rain that fell directly over Hazel Grove resulted in relatively little impact in terms of surface water flooding, the impact of the rain that fell on the catchment of Poise Brook and drained to the river was much more detrimental.

From the local rain gauge record, Section 2.2.2, it is possible that rain fell continuously on the Poise Brook catchment for up to eight hours on 11 June. Comparing the catchment of Poise Brook (in the left of Figure 4.2) with the rainfall radar snapshot (to the right), it can be seen that the entirety of the catchment area draining to Poise Brook (and Hazel Grove Brook) was also located within the most intense part of the storm at one time. These rainfall conditions, combined with already saturated ground conditions (which would have converted more of the rainfall directly into runoff) would have allowed the levels on Poise Brook (and Hazel Grove Brook) to build and stay high for long enough for significant volumes of water to spill out of bank, resulting in the flooding observed.

Data from the water level gauge at the Poise Brook reservoir would suggest that the river took a couple of hours to fully respond to the rain that fell on the catchment; water levels were shown to rise sharply starting from around 13:30 until they reached their peak at 16:00. It is likely that Hazel Grove Brook responded in a similar manner.

Starting upstream, Hazel Grove Brook burst its banks within Torkington Park and flooded the park. The wall between Torkington Park and Torkington Road was overtopped, flooding the road and two properties internally. This flood water passed onto and flowed north along Hazelwood Road; it is understood that this flood water caused only highway or driveway flooding. This flooding mechanism is illustrated in Figure 4.3.

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Figure 4.3 : Hazel Grove Poise Brook flood flow routes

Hazel Grove Brook is culverted under Torkington Road from the downstream end of Torkington Park. The debris screen located at the culvert inlet became blocked during the flood event; it is possible that the material causing the blockage originated from the trees along the river bank within the park, although this is not confirmed. The EA were alerted to the presence of a blockage by the remote alarm fitted to the screen and operatives were sent out to clear the screen during the event. The blockage may have contributed to the elevated levels of Hazel Grove Brook within Torkington Park during the flood event, before it was cleared. (It is noted that with forecasts of the storm event, the EA cleaned the Torkington Park debris screen a few days before 11 June in preparation for a flood event on Poise Brook. It is therefore likely that the blockage occurred during the event and was not present at the start of the event).

Downstream of the Torkington Road culvert, Hazel Grove Brook spilled out of bank and directly flooded the gardens of several properties on Hazelwood Road and five properties internally. The rear of 23 properties on Nelson Street (See Figure 4.1) were also flooded directly from Poise Brook.

Regarding the impact of new development within the area on local flood risk, the catchment of Poise Brook does not extend outside of the Stockport borough, so only development within the borough could potentially impact the flood risk on this watercourse. Construction of the A6 Manchester Airport Relief Road (A6MARR) was ongoing at the time of the June flooding events. A section of this road is being constructed within the runoff catchment of Poise Brook, further upstream from Torkington Park. Earthworks for this section of the new road were being undertaken during June 2016 and included some earthworks drainage to Ox Hey Brook (upstream of Hazel Grove Brook) via an attenuation pond. It is considered unlikely that the construction works contributed a significantly greater volume or rate of runoff to Ox Hey Brook compared to a pre-construction case, and thus had a negligible impact on the flooding from Hazel Grove Brook. As per the earlier comment regarding the impact of the A6MARR on the flooding at Bramhall, it is a planning condition that the scheme must not increase the local risk of flooding.

D01 16 June 2016 Flood Events

Approximately 1 km of the Macclesfield Canal passes through the catchment of Hazel Grove Brook; it is not understood how the canal responded to the 11 June storm event, nor if overflows or discharges from the canal contributed to the flows on Poise Brook.

4.3 RMA Responses

The following information has been collected regarding the RMA responses both during and following the 11 June 2016 flooding event in Hazel Grove. The lists are not necessarily comprehensive and may not cover all actions taken by the RMAs.

During the flooding event:  Solutions SK (SMBC’s environmental services provider) carried out road closures of Torkington Road and Hazelwood Road during the event at the request of the police and put in place diversions.  SMBC delivered sandbags to Torkington Road and Torkington Park (period 17:00 on 11 June to 01:30 on 12 June).  SMBC established an evacuation centre at Hazel Grove Life Centre (later closed as all residents who evacuated had accommodation).  The flooded area in Hazel Grove is covered by the River Mersey Uplands catchment Flood Alert area; the EA put in place a Flood Alert at 19:42 on 11 June and was cancelled at 08:28 on 16 June. This area is also covered by the Flood Warning Area for Poise Brook, however no Flood Warning was issued for the 11 June flooding event.  EA attended site to clear the Torkington Park debris screen. Following the flooding event:  SMBC clean-up operation (including highway surface and drainage clearance, and clean-up of Torkington Park).  SMBC investigating impact of materials washed away from A6MARR construction sites on local watercourses.  SMBC provided skips for residents clean-up.  SMBC site inspection at Bramhall Park, Bramhall roundabout and along Lady Brook.  SMBC commissioned this S19 report.  SMBC set up a Recovery Coordination Group which helped support affected residents and businesses.  EA door-to-door survey of flood impacts  UU surveyed the local sewer network but found no evidence of any blockages within the system that could have contributed to the flooding.

D01 17 June 2016 Flood Events

4.4 Recommended Actions

Based on the analysis of the June 2016 flooding events in Hazel Grove, the following actions are recommended to the local RMAs:

Table 4.1 : Recommended actions for Hazel Grove

RMA Recommended Action

Maintain efficient operation of highway drains. SMBC Highways Department Consider options to provide additional highway drainage in the Kintore Avenue area Consider provision of Property Level Protection for properties at risk Consider maintenance regime within Torkington Park (specifically SMBC as LLFA clearance of debris on watercourse banks) A6MARR – review approach to flood risk during construction and whether appropriate mitigation measures were in place Maintain efficient operation of surface water and combined sewers United Utilities Review options to provide additional capacity in local surface water sewers Consider options to reduce fluvial flood risk on Hazel Grove Brook. Review Flood Warnings and trigger levels for the Poise Brook flood Environment Agency warning area Review performance of Torkington Park debris screen during event (e.g. was bypassing of the blockage possible?) Property Owners Consider installation of Property Level Protection SMBC as LLFA Continue to manage flood risk from new development. Seek flood risk Environment Agency benefits from new development where possible.

D01 18 June 2016 Flood Events

5. Offerton Green

5.1 Site Overview & Flooding Impacts

Offerton Green is a suburb of Stockport and is located between Marple to the east and Hazel Grove to the south. Poise Brook, an EA main river, flows in a northerly direction through the area. The river flows adjacent to Minsmere Walks, flows under and then follows Bean Leach Road for approximately 300 m before meandering away from Bean Leach Road and onwards towards its confluence with the River Goyt. Hazel Grove is located approximately 500 metres upstream of Offerton Green.

Two separate flooding events occurred in Offerton Green during June 2016: one event on 8 June and one three days later on 11 June. 44 residential properties were affected by flooding on 8 June, 17 of which suffered internal flooding; the properties impacted were located on Shearwater Road and Fulmar Drive.

Figure 5.1 : Offerton Green site overview

67 residential properties suffered flooding on 11 June in Offerton Green, nearly all of which (65) suffered internal flooding, leading to the evacuation of some of the local residents. Flooding was concentrated in two areas: around Shearwater Road and Fulmar Drive, where 23 and 25 properties respectively flooded internally, and at Minsmere Walks where 12 properties flooded internally. Internal property flooding was also reported at three properties on Bean Leach Road and at two properties on Teal Close.

The Greater Manchester Fire Service attended the scene and was supported by the North West Ambulance Service Hazard Area Response Team (HART) and also by Mountain Rescue. As a result of the flooding, several local roads including Shearwater Road, Bean Leach Road and Fulmar Drive were closed to traffic.

D01 19 June 2016 Flood Events

5.2 Flooding Analysis

5.2.1 8 June 2016

Reports from UU indicate that on 8 June 2016 the surface water sewers in the Offerton Green area were overwhelmed by the intensity and duration of rain that fell on the suburb. As a result rainfall pooled and caused external and internal flooding to properties in the area. Offerton Green has been highlighted on the snapshot of the rainfall radar at its peak during this storm event in Figure 5.2; this confirms that the area received particularly intense rainfall during this event

UU reports that levels in Poise Brook were also high during this event; this may have affected the outfall of the local surface water sewer, reducing the capacity of the sewer and contributing to the observed flooding. Levels were not elevated at the Poise Brook reservoir on 8 June; as this gauge is not situated directly on the river itself it neither confirms nor refutes UU’s statement on levels at the outfall.

Figure 5.2 : Radar rainfall intensities at 15:05 on 8 June 2016 at Offerton Green

Offerton Green

(Source: Environment Agency)

5.2.2 11 June 2016

Three days later on 11 June Offerton Green was hit again by flooding, however this time from both surface water flooding and fluvial flooding from Poise Brook. The information available on the timeline of events suggests that the area was first impacted by surface water flooding, then later by river flooding.

Similar to the flooding event of 8 June, the UU surface water sewer was overwhelmed following prolonged intense rainfall, resulting in surface water flooding and sewer flooding. The rainfall radar snapshot at 14:00 on 11 June, presented in Figure 5.3, shows that Offerton Green was located within a large area of extremely intense rainfall within the storm; up to 78 mm/hour was recorded at the most intense area of rainfall.

Figure 5.3 also indicates that the entirety of the Poise Brook catchment was subject to the worst impacts of the storm at this time. Data from the water level gauge at the Poise Brook reservoir suggests that the river took a couple of hours to fully respond to the rain that fell on the catchment; water levels were shown to rise sharply starting from around 13:30 until they reached their peak at 16:00. This would correlate with reports from the residents of surface water and sewer flooding first in the day, followed by river flooding later.

D01 20 June 2016 Flood Events

The rise in water levels on Poise Brook is likely to have further impeded the local surface water sewer outfall, impacting the capability of the sewer to drain effectively.

Figure 5.3 : Radar rainfall intensities at 14:00 on 11 June 2016 at Offerton Green

Offerton Green

(Source: Environment Agency)

The flood flow routes from Poise Brook into the housing estate are presented in Figure 5.1. The figure shows that an embankment is found adjacent to Minsmere Walks; this is currently classed as a flood defence by the EA, but recent discussions with the EA indicate that this is a misclassification. It is understood that the embankment is a spoil mound created during construction of the housing estate a few decades ago. The embankment is not a formal flood defence and neither is it effective as a defence; on 11 June Poise Brook spilled out of bank upstream of the Bean Leach Road crossing, flood water was directed onto Bean Leach Road by the embankment, following which flood water bypassed the embankment and flowed onto the housing estate located behind.

Inspection of the topography of Offerton Green reveals that Shearwater Road, Fulmar Drive and Teal Close (where the majority of properties were flooded) are located in the lowest area of Offerton Green. The EA Risk of Flooding from Surface Water map shows that runoff from the Offerton Green area naturally flows towards this area and collects. Bean Leach Road also lies at a higher elevation than the adjacent area of the housing estate, so consequently if Poise Brook floods onto Bean Leach Road, flood water will naturally flow towards the lower lying areas of housing.

As Hazel Grove Brook becomes Poise Brook upstream of Offerton Green, the same comments made regarding the impact of development in the area and the construction of the A6MARR on the risk of flooding in Hazel Grove also apply to Offerton Green. Construction of the A6MARR is considered to have had a negligible impact on the flooding from Poise Brook in Offerton Green on 11 June 2016.

D01 21 June 2016 Flood Events

Figure 5.4 : Poise Brook flood flow routes – 11 June 2016

UU attended site in response to the 8 June and 11 June flood events and surveyed the local sewer network but found no evidence of any blockages within the system that could have contributed to the flooding. UU confirmed that the local surface water sewers were overwhelmed in response to the rainfall events.

A visit to site on 06 September 2016 found that the outfall for the surface water sewer draining this area was submerged to approximately half the bore of the pipe. Given that a period of dry weather was being experienced at the time of the site visit, this would indicate that the sewer would not be able to discharge effectively during a storm event, meaning that the system would not perform at maximum efficiency.

5.3 RMA Responses

The following information has been collected regarding the RMA responses both during and following the 11 June 2016 flooding event in Offerton Green. The lists are not necessarily comprehensive and may not cover all actions taken by the RMAs.

During the flooding event:  Solutions SK (SMBC’s environmental services provider) carried out road closures of Fulmar Drive, Carrwood Road, Bean Leach Road, Poise Brook Road, Minsmere Walks, Dunnock Close and Shearwater Road during the event at the request of the police and put in place diversions.  SMBC delivered sandbags to Fulmar Drive, Bean Leach Road, Shearwater Road, Minsmere Walks, Dunnock Close, Poise Brook Road (period 17:00 on 11 June to 01:30 on 12 June).  SMBC established an evacuation centre at Hazel Grove Life Centre (later closed as all residents who evacuated had accommodation).  SMBC attended site – individual properties visited and residents assisted.

D01 22 June 2016 Flood Events

 The flooded area in Offerton Green is covered by the River Mersey Uplands catchment Flood Alert area; a Flood Alert was put in place at 19:42 on 11 June and was cancelled at 08:28 on 16 June. This area is also covered by the Flood Warning Area for Poise Brook, however no Flood Warning was issued on either 8 June or 11 June.  Pumping of Minsmere Walks (fire service). Following the flooding event:  SMBC clean-up operation (including highway surface and drainage clearance).  SMBC provided skips for residents clean-up.  SMBC liaising with EA and UU with respect to flooding.  UU provided clean-up service to residents.  UU surveyed and cleaned the local sewers.  SMBC, UU and EA attended site at Shearwater Road to establish engineering works required (5 July).  SMBC commissioned this S19 report.  UU planning to undertake sewer modelling exercise to understand flooding mechanism.  SMBC set up a Recovery Coordination Group which helped support affected residents and businesses.  EA door-to-door survey of flood impacts

5.4 Recommended Actions

Based on the analysis of the June 2016 flooding events in Offerton Green, the following actions are recommended to the local RMAs:

Table 5.1 : Recommended actions for Offerton Green

RMA Recommended Action

Ensure necessary maintenance is carried out to local highway drains SMBC Highways Department following flood events Maintain efficient operation of highway drains. SMBC as LLFA Consider provision of Property Level Protection for properties at risk Maintain efficient operation of surface water and combined sewers Review options to provide extra capacity in the surface water sewer United Utilities (particularly in relation to surface water sewer outfall) Ensure effective communication with SMBC regarding flooding events/ potential flood issues Consider options to reduce fluvial flood risk on Poise Brook. Review Flood Warnings and trigger levels for the Poise Brook flood Environment Agency warning area Review Flood Zones following reclassification of ‘flood defence’ Property Owners Consider installation of Property Level Protection SMBC as LLFA Continue to manage flood risk from new development. Seek flood risk Environment Agency benefits from new development where possible.

D01 23 June 2016 Flood Events

6. Edgeley

6.1 Site Overview & Flooding Impacts

During the evening of 16 June 2016 six properties on Oak Street, Edgeley, suffered surface water flooding; three flooded internally. Highway, pavement and driveway flooding occurred at the eastern end of Laburnum Way, and the junction of Myrtle Street and A560 Brinksway was also impacted by the pooling of surface water. As a surface water only flooding event, the EA was not required to respond to this event.

Figure 6.1 : Edgeley site overview

6.2 Flooding Analysis

Radar data of this rainfall event is not available to the study; however, the Meadowbank School rain gauge is located approximately 2 km from this area of Edgeley and should provide a good representation of the storm at this location. The rain gauge data shows that rain fell for approximately two hours starting at 17:00 and that the peak rainfall intensity reached nearly twice that of 8 June and over three times that of 11 June. The timing of the storm correlates with accounts from residents of the flooding occurring in the evening.

The main source of rainfall runoff understood to have contributed to the flooding at these locations is understood to be Bonar Park (labelled Recreation Ground in Figure 6.2). Heavily saturated ground conditions are likely to have converted a significant proportion of the rain that fell on the park into runoff. This area slopes quite steeply (generally) to the north west, towards the River Mersey. The runoff from the park is reported to have flowed directly onto Myrtle Street and through the alleyways behind Laburnum Way and onto Laburnum Way itself, as illustrated in Figure 6.2.

D01 24 June 2016 Flood Events

A blockage was present at the time of the event in the main surface water sewer flowing north-west along Myrtle Street. As a result of the blockage, the highway drainage on Myrtle Street would have been ineffective at the time of the storm event. Surface water is reported to have flowed down Myrtle Street and onto Oak Street, resulting in property flooding, and also onwards to the junction with Brinksway, where it pooled and caused highway flooding.

30 or 40 metres from the junction of Laburnum Way and Myrtle Street, Laburnum Way slopes towards the termination of the road to the east. The surface water drainage on Laburnum Way connects into the sewer on Myrtle Street, and due to the blockage the highway drainage would have been ineffective in removing the runoff from the park, causing it to pool at the low end of Laburnum Way.

UU attended site during the flooding event and removed the blockage from the Myrtle Street sewer to allow flood waters to drain down. In the days following the flood event UU also inspected the local sewers and undertook root removal. The requirement for remedial work on the Myrtle Street sewer has been identified and options are currently being reviewed by UU. SMBC is also aware that many of the gullies on the paths in Bonar Park and alleyways behind Laburnum Road are blocked, and that the land drainage within the park itself requires maintenance.

SMBC has on record a history of flooding to Laburnum Way and to the rear gardens of the properties on Oak Street; however, the extent and severity of the 11 June 2016 was unprecedented.

Figure 6.2 : Edgeley rainfall runoff flow routes

D01 25 June 2016 Flood Events

6.3 RMA Responses

The following information has been collected regarding the RMA responses both during and following the 11 June 2016 flooding event in Offerton Green. The lists are not necessarily comprehensive and may not cover all actions taken by the RMAs.

During the flooding event:  SMBC contractor attended site.  UU attended site and cleared blockage from Myrtle Street sewer, allowing flood water to drain. Following the flooding event:  UU attended site and removed tree roots from the surface water sewer.  SMBC investigation of flooding issues.  Blocked gullies and land drainage issues on Bonar Park reported to SMBC Greenspace Team.

6.4 Recommended Actions

Based on the analysis of the June 2016 flooding events in Edgeley, the following actions are recommended to the local RMAs

Table 6.1 : Recommended actions for Edgeley

RMA Recommended Action

Ensure necessary maintenance is carried out to local highway drains SMBC Highways Department following flood event Maintain efficient operation of highway drains. Consider options to improve drainage of Bonar Park and surrounding pavement drainage Consider options to increase highway drainage capacity (e.g. additional SMBC as LLFA gullies or combined kerb and drainage solutions) Consider options to direct runoff safely away from properties (e.g. raised kerbs on Myrtle and Ash Street) Consider provision of Property Level Protection for properties at risk Maintain efficient operation of surface water and combined sewers Review options to provide extra capacity in the surface water sewer (currently being undertaken) United Utilities Review cause of blockage and how to prevent in the future Ensure effective communication with SMBC regarding flooding events/ potential flood issues Property Owners Consider installation of Property Level Protection SMBC as LLFA Continue to manage flood risk from new development. Seek flood risk Environment Agency benefits from new development where possible.

D01 26 June 2016 Flood Events

7. Other Incidents

7.1 High Lane

Four properties in High Lane are reported to have suffered external flooding on 11 June 2016. High Lane Brook flows east to west through High Lane. A blockage at the inlet of the culvert carrying High Lane Brook under Windlehurst Road caused the watercourse to spill out of bank, across Windlehurst Road and return back to channel, flooding the gardens of three properties in the process. The blockage has since been cleared from the culvert inlet by the EA. One further property on Windlehurst Road is also understood to have suffered external flooding as a result of sewer flooding during this event.

7.2 Infrastructure Impacts

The storm event of 11 June caused significant disruption to the local highway network within the Stockport borough. Table 7.1 lists the roads that were closed during the event. Other roads, not listed, were affected by flooding but not closed.

Table 7.1 : Road closures on 11 June 2016

Road closure Reason

Torkington Road Fluvial flooding Hazelwood Road Fluvial flooding Bridge Lane & Bridge Lane Roundabout Surface water flooding and fluvial flooding Shearwater Road Surface water flooding and fluvial flooding Fulmar Drive Surface water flooding and fluvial flooding Carrwood Road Presumed surface water flooding Bean Leach Road Fluvial flooding Minsmere Walks Surface water flooding and fluvial flooding Dunnock Close Presumed surface water flooding Macclesfield Road Norbury Bridge deemed unsafe Road Presumed surface water flooding

Significant disruption was also caused on the Stockport to Disley railway line following a landslip at Middlewood Station on 11 June 2016; according to Network Rail 6000 tonnes of earth was displaced from the track6. This resulted in the closure of the line for two weeks from 11 June 2016 till 25 June 2016, when it was reopened following repairs.

6 Network Rail website news article: https://www.networkrail.co.uk/news/2016/jun/railway-buxton-manchester-reopens-after-landslip/ (accessed 22/08/2016)

D01 27 June 2016 Flood Events

8. Conclusion

This report has been produced to document the findings of the Section 19 Investigation into the June 2016 floods in Stockport, undertaken on behalf of SMBC under Section 19 of the Act. Its main aim was to identify those communities affected, to determine why they were affected, and to recommend actions for each RMA.

Severe storms during June 2016 resulted in flooding across the borough of Stockport. The most widespread flooding occurred on 11 June when prolonged heavy rainfall caused local watercourses to spill out of bank and surface water drainage systems to become overwhelmed. 141 properties across Bramhall, Hazel Grove, Offerton Green and High Lane were affected by flooding, many roads were closed and services on railway lines disrupted due to line damage. Flooding events also occurred on 8 June and 16 June, however these incidents were more localised and caused only by surface water and sewer flooding.

The key drivers to the 11 June flooding event are considered to be:  Heavy rainfall in the days leading up to 11 June creating highly saturated ground conditions, meaning that a significant proportion of the rainfall on 11 June was converted into runoff and entered local watercourses;  Prolonged rainfall on 11 June, which gave the local watercourses time to respond and allowed water levels to rise significantly, with consequent fluvial flooding of properties  Intense rainfall rates on 11 June which overwhelmed local surface water drainage systems, with consequent surface water flooding of properties

The storm events of 8 June and 16 June are shown to be much shorter in duration than 11 June, however the intensity of rainfall was much greater. Property flooding was caused on 8 June in Offerton Green as a result of the local surface water sewers being unable to drain the sheer volume of rainfall runoff. In Edgeley on 16 June, property flooding resulted from a combination of blockages in the local drainage network and significant volumes of runoff generated from the saturated ground of Bonar Park.

Based on the analysis of the flooding events made in this report, actions have been recommended to each RMA on a site-specific basis; these are found under the relevant section of the report. The delivery of these actions will be heavily dependent on funding availability and other RMA priorities. Some work has already been carried out or is already planned by the RMAs in response to the flooding events.

D01 28