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Flood Investigation Report Section 19, Flood & Water Management Act (2010)

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Flood Investigation Report Section 19, Flood & Water Management Act (2010) Upper Calder Valley 29 th July 2013 Flooding Incident Control Sheet Project Title:
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Flood Investigation Report Section 19, Flood & Water Management Act (2010) Upper Calder Valley 29 th July 2013 Flooding Incident Control Sheet Project Title: Flood and Water Management (2010) Act Section 19 Flood Investigation Document Title: Upper Calder Valley 29 th July 2013 Flood Investigation Report Document No: 1 Revision: Final Issue Control Name Signature Date Written Paul Lambert Checked Howard Glenn Approved David Turner Authorised for Issue Issue Status David Turner Final Issue History Rev. Issue Author Date Checked Date Approved Date Authorised Date 1 Draft PL HG DT - DT - 2 Draft v2 PL HG RJ Final PL HG - Highways & Engineering December 2013 This page has been left blank intentionally Executive Summary On the 29 th July 2013, large storm cells brought heavy rainfall to the Pennine region. In Calderdale, the upper valley area was badly affected by flooding from a variety of sources. The communities and infrastructure worst affected by the flooding were principally those located in the Upper Calder Valley immediately adjacent to the Walsden Water and River Calder. The towns and villages impacted the most were Walsden, Todmorden and Hebden Bridge. The key infrastructure affected was Caldervale line at Walsden Station, a culvert on a subcatchment watercourse on the Walsden Water and highway and drainage infrastructure on the Rochdale (A6033) and Burnley Road (A646). In response to the flood event this Section 19 - flood investigation report has been completed by Calderdale Metropolitan Borough Council (CMBC) as the Lead Local Flood Authority (LLFA), under the duties set out in Section 19 of the Flood & Water Management Act (2010). It was deemed necessary to complete an investigation as properties and infrastructure were badly affected during this storm event. A large data collection exercise was undertaken between key stakeholders, CMBC and third parties to gain understanding of the flood mechanisms, extent of flooding, damage assessment and flooding response. Approximately 151 properties have been directly affected by the flood event. The report has identified the key areas that were mainly affected and the mechanisms that caused the flooding in those areas. The main flood mechanisms have been identified as; The two watercourses Fir Wood Clough and Fir Wood Drain located on the hillside above Kershaw Road, Walsden were unable to convey flood flows and suffered severe erosion, overloading and blocking the land drainage system, Excess surface water from the damaged culverts on Kershaw Road, Walsden spilled onto the Caldervale line at Walsden Station and onto Rochdale Road damaging infrastructure and flooding properties, Excess surface water from hillside runoff and sub-catchment watercourses causing damage along Bacup Road and flooded property and infrastructure along Rochdale Road, A partially blocked culvert on the Walsden Water, as the result of the collapse of temporary works during the flood event, flooded property and infrastructure on the Walsden Water, Overtopping of Birks Clough, Walsden flooding Rochdale Road, Excess runoff from sub-catchment watercourses and hillside runoff flooding properties along Burnley Road and adjacent streets, Rainfall and surface water overwhelmed the design capacity (1 in 30 year event) of the sewers and highway drainage (1 in 2 year event), although the sewerage infrastructure suffered little damage, A hydrological analysis was undertaken by the Environment Agency (EA) for this storm event. This has identified the key hydrological evidence, which is included in this report. i This report has identified the relevant risk management authorities and their roles and responsibilities for flooding in accordance with the Flood & Water Management Act (2010). The report summarises the activities risk management authorities have undertaken according to their roles and responsibilities. The report recognises the roles of riparian and property owners which assign a certain level of responsibility to those owners to anticipate flooding where risk has been identified and to take appropriate measures. This is also recognised by Government through the partnership funding system and various acts of parliament. For this flood event risk management authorities have responsibilities for ; EA general overview of Flood Risk Management and partnership with other RMAs. Works taking place on the Walsden Water as part of Phase 3 of the Todmorden and Lower Walsden Flood Alleviation Scheme. LLFA (CMBC) - compliance with Flood and Water Management Act 2010 in particular preparing this report. Bringing forward FRM proposals to be included in the EA Medium Term Plan and reacting to urgent situations requiring capital solutions in partnership with other RMAs. Highway Authority (CMBC) maintaining adequate highway drainage and acting as riparian owner of culverts crossing the highway. Yorkshire Water maintaining the sewer network in serviceable condition and bringing forward improvement schemes as found necessary in partnership with other RMAs. Network Rail ensuring integrity and serviceability of the railway network and working in partnership with other RMAs to reduce risk. Riparian owners maintaining their assets to the standard required by the Land Drainage Act 1991 and cooperating with the LLFA as necessary to facilitate progress of revenue and capital proposals brought forward in the community interest. Property owners making their property as resistant and resilient to flood risk as possible. Flood events provide the opportunity to introduce resilience measures in conjunction with their insurers who are now beginning to recognise the value of doing more than replacing like with like. Insurance companies fulfilling the terms of their insured s policies. It is the conclusion of this report that all these responsibilities have been or are in the process of being discharged to a greater or lesser extent. All flood risk management authorities, strategic partners and community groups have undertaken activities to restore the Upper Calder Valley to a working order. All mitigation measures have been implemented. Capital works or investigations have been identified and are subject to the availability of resources. This report shows the significant contribution each risk management authority, volunteer groups, community groups and local businesses has made during and post-flood event. Sub-catchment watercourses, Main River and the sewer network have played a pivotal role in this flood event. The EA, CMBC and Network Rail are developing options to mitigate the flood risk in areas affected by the flooding identified in this report. Many of the areas of concern have been identified on the long term Calder ii Valley Flood Investment Plan, which CMBC and partners are developing and implementing. iii iv Acknowledgements The Council would like to thank Yorkshire Water Services Ltd, the Environment Agency, Network Rail and the Canal & River Trust for their assistance in this investigation. The Council would also like to thank members of the Calderdale community, businesses and community groups for their on-going assistance and support in the aftermath of the flooding on the 29 th July. v This page has been left blank intentionally vi Table of Contents 1. Introduction Background Flooding Location History of Flooding Flooding Incident Flood Warnings and Alerts Risk Management Authorities Immediate Response Data Collected Areas Affected Walsden Todmorden Rainfall Analysis River Levels and Flows Roles, Responsibilities and Post Flood Event Activities Environment Agency Lead Local Flood Authority Water and Sewerage Company Riparian and Property Owners Network Rail Canal & River Trust Property Owners Conclusions References 1. Introduction 1.1. Background An investigation into the flood event on the 29 th July 2013 is required as approximately 151 properties were affected by the flooding in the Calderdale area. The main affected areas of the event were Walsden and Todmorden. There was significant disruption and damage to properties and key infrastructure including highway and drainage infrastructure and the Caldervale Line. Calderdale Metropolitan Borough Council (CMBC) as the Lead Local Flood Authority (LLFA) has a responsibility to record and report flood incidents in accordance with Section 19 of the Flood and Water Management Act (2010): (1) On becoming aware of a flood in its area, a LLFA 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 (a) Publish the results of its investigation, and (b) Notify any relevant risk management authorities. This report summarises the flood mechanisms, extent of flooding, damage assessment and flooding response in Walsden, Todmorden and outlying areas that were affected. This report outlines the basic responsibilities of the risk management authorities involved, outlines their response to the flood event and identifies any potential future actions. 2 1.2. Flooding Location The communities and infrastructure worst affected by the flooding were principally those located in Walsden Shade and Salford areas of Todmorden adjacent to the Walsden Water (see Figure 1). The key infrastructure affected was the culverted watercourses (Fir Wood Clough and Fir Wood Drain) at Kershaw and Clough Road in Walsden, Caldervale line at Walsden Station and highway drainage infrastructure on the Rochdale (A6033) and Burnley Road (A646).. N Todmorden Main affected areas Walsden Figure 1 Location of the communities affected by July flooding 1.3. History of Flooding Calderdale has a long history of flooding from a variety of sources including surface water flooding (pluvial), river (fluvial) or a combination of these. Significant fluvial and pluvial flooding has occurred in the recent past particularly 3 2000, 2006, 2007, 2009, 2011and Due to the nature of the topography in the Upper Calder and Walsden Valleys, surface water collects quickly in the valley bottom because of steep valley sides and rapid runoff from thinly vegetated and impermeable surfaces. The majority of the historical pluvial and fluvial flooding has occurred in the winter and has been the result of a period of prolonged heavy rainfall. However, more frequent annual surface water and fluvial flooding has occurred in the summer months as a result of short duration, high intensity storm events. The most recent example being the two flood events that occurred in the summer of The main areas affected by flooding in this event have been affected by similar flooding in previous events. In 2006 Kershaw Road suffered a major rainfall event, which resulted in damage and subsequent significant repair to the Kershaw Road culvert in Walsden station and surrounding properties were greatly affected by fluvial and surface water flooding in the flood events during the summer of Birks Clough overtopped the river channel adjacent to the Rochdale Road on two occasions in the summer of Scott Street and adjoining streets have a history of flooding from hillside runoff. There is currently a land drainage system that is not sufficient to convey excess surface water runoff from the hillside in this location. The Shade and Salford areas of Todmorden have also been badly affected by severe flooding in the summer of Burnley Road has flooded on several occasions in the past and particularly in the locations identified in this report. 4 2. Flooding Incident 2.1. Flood Warnings and Alerts A number of flood warning communications were received by CMBC and the local community prior to the 29 th July flood event. The key communications are summarised below: 27 th July 10:30hrs The Meteorological Office (MO) and EA (Flood Forecasting Centre) issued a Flood Guidance Statement (FGS) indicating the overall river flood risk and surface water flood risk is Low for England. There is potential for intense, thundery downpours, which may move north overnight into Sunday 28 th July. 27 th July 16:00hrs The MO and EA (Flood Forecasting Centre) issued a FGS indicating an overall Medium flood risk for Durham, Tyne and Wear and Northumberland for surface water and river flooding. A Low flood risk remains for the rest of England and Wales. 28 th July 10:00hrs - The MO and EA (Flood Forecasting Centre) issued a FGS indicating the overall flood risk was Low to Very Low for the whole country. 29 th July 14:30hrs The MO and EA (Flood Forecasting Centre) issued a FGS indicating there was an overall Low flood risk from river and surface water flooding. However, there is a Medium flood risk of river and surface water flooding in the Yorkshire region. Showers currently affecting England and Wales are locally heavier than expected and therefore expect some minor disruption. 30 th July 10:30hrs The MO and EA (Flood Forecasting Centre) issued a FGS indicating there was a Medium risk of minor disruption due to surface water flooding in the Yorkshire region. The EA issued a Flood Alert for the Upper Calder at 17:44hrs on the 29 th July. A flood warning was issued for the Walsden Water at Walsden. A Flood Warning was issued again at 18:31hrs for the Walsden Water and this triggered the flood warning sirens. A Flood Warning update was issued at 21:30hrs. The all clear was issued at 08:31hrs the following morning of the 30 th July. 5 EA flood warnings are available on the Calderdale Website, please use the following link; Risk Management Authorities Immediate Response A summary of the activities risk management authorities undertook during and immediately after the 29 th July Flood Event is given below:- Calderdale Metropolitan Borough Council On the advice of the Flood Forecasting Centre CMBC teams were on standby throughout the weekend prior to the flood event on the 29 th July. CMBC implemented relevant emergency plans during and after the flood event. Representatives from all emergency services, Stakeholders and CMBC teams were present to coordinate a proactive response to the flooding. Additional Council resources were retained throughout the week to support the post clean up operation. The Calderdale Community Recovery Framework was activated immediately following the floods. Drainage contractors were deployed across the borough during and immediately after the peak of the flood event to assist in the clean up operation. Following the flood event Council Services were dealing with an exceptionally high volume of flooding issues ranging from collapsed and blocked culverts to internal flooding to gully defects. Drainage gangs worked to unblock drainage infrastructure across the borough. However the main focus of activity was concentrated in the worst affected communities of Walsden and Todmorden. Network Rail The rail network was significantly disrupted by flood water between Summit Tunnel and Walsden Station. Train services were cancelled for the duration of the emergency works to the track. A replacement bus service was put into operation during the repair works. Yorkshire Water Yorkshire Water operational staff was on alert following the weather warnings throughout the weekend and on the 29 th July. YW engineers implemented 6 appropriate measures in preparation for heavy, thundery showers. YW contractors worked to remove silt / debris from sewer systems and maintain sewer capacity. Environment Agency The main river network was mainly unaffected in the 29 th July flood event. The EA provided support and resources to help coordinate the emergency response and recovery plan during and after the flood event. The EA provided immediate additional resources to support the other risk management authorities. Note: Canal & Rivers Trust is not identified as a risk management authority under the Flood & Water Management Act (2010) but it is a significant stakeholder and an essential contributor to any multi-agency response. However, the canal network was unaffected by this rainfall event Data Collected A data collection exercise was carried out after the flood event by the following partners:- The Environment Agency, CMBC, Emergency Services, Network Rail, Canal & River Trust, Yorkshire Water Services, The Meteorological Office Flood Forecasting Centre. The data provided includes: Flood warning and guidance information, Hydrological data including rainfall totals and river flows and levels, Reports from officers and operatives of what happened during the flood event, Reports logged at CMBC customer contact centre, 7 Photographs and video footage from CMBC, network rail and the EA including CCTV and footage from the internet, Surveyed data of the flood damage taken by the EA and CMBC, Online news reports, Flood extent outlines plotted from observed flood levels and local knowledge. 8 3. Areas Affected A high intensity, localised storm fell on the 29 th July in the Upper Calder Valley. The greatest impact was felt in Walsden at Walsden Station and the Shade and Salford areas of Todmorden. Approximately 151 residential and business properties were flooded, surface water overwhelmed drainage and sewerage systems, a major culvert collapsed in Walsden and excess surface water runoff and a significant blockage at a culvert entrance on the Walsden Water in Shade, caused flooding to parts of Todmorden. The impacts of the rainfall are examined in more detail below and illustrated in Appendix A for the Kershaw Road area in Walsden and Appendix B for Shade, Todmorden area Walsden Kershaw, Clough Road and Walsden Station High intensity, localised rainfall fell in the Upper Calder Valley between Walsden and Todmorden. Two rainfall events occurred during Monday 29 th July at 10:15 to 11:20 and 16:00 to 17:00. The peak rainfall fell within a few minutes, which caused a surge of surface water runoff into the valley generating hillside runoff and overloading watercourses. In Walsden, Walsden Station and residents on Kershaw Road and adjoining streets were greatly affected by the high intensity rainfall. Two watercourses Fir Wood Clough and Fir Wood Drain, take water directly from the upland moorland area of Oatley Hill and Burnt Hills above Walsden. The two watercourses flow into separate culverts, which converge to a single culvert under properties along Kershaw Road. The culvert then transports flows under Clough Road, through a short section of open channel, which then passes under the railway line and the A6033 into the Walsden Water. Refer to Appendix A for more details. Large boulder material blocked the culvert under Kershaw Road resulted in the culvert surcharging immediately behind 1 and 3 Melbourne Road. This resulted in a collapse of the main culvert in Kershaw Road adjacent to 1 Calf Hey Terrace. Excess surface water and debris from the collapsed structures overflowed onto Clough Road and adjoining streets, causing significant damage to the highway and nearby properties. 9 Figure 2 Debris from the collapsed culverts onto adjacent property Figure 3 Kershaw and Clough Road, road surface severely damaged as a result of the excess surface water on Clough Road. At the lower end of Clough Road the excess surface water could not flow back into the watercourse and therefore spilled onto the railway track, flooding the rail 10 track at Walsden Station. Similar to the summer 2012 events the excess surface water spilled onto Rochdale Road and flooded the highway and adjacent properties. The track at Walsden station suffered significant damage. Several properties were flooded and Rochdale Road was closed temporarily until the following morning, while the authorities made safe the area and cleaned the highway. The sewer and gullies along Rochdale Road were cleaned immediately after the event. F
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