Flood Investigation Report

Somerset County Council Lead Local Flood Authority

Parsonage Lane, The Street, Church Lane, Broadway and Greenditch Close, Chilcompton 17 th June 2016

Final Draft January 2017

Revision Schedule

Checked Rev Date Details Author Approved by by Draft for 1 06/10/16 stakeholder A. Lambart consultation

2 16/01/17 Final draft A. Lambart D. Martin D. Martin

Table of Contents

Executive Summary ...... 1 1. Introduction ...... 2 & 3 2. Risk Management Authority Responsibilities ...... 4 2.1. Recording Flood Incidents ...... 4 2.2. Key Responsibilities ...... 4 3. Flood Incident Summary and Impact ...... 5 3.1. Site Location ...... 5 3.2. Site characteristics and drainage ...... 6 4. Drainage and Flood History ...... 8 4.1. Previous Flood Incidents ...... 8 4.2. Flood incident of 17 th June 2016 ...... 9 4.3. Rainfall Analysis ...... 10 5. Probable Cause ...... 111 5.1. Heavy rainfall in a relatively short period of time ...... 11 5.2. Housing within the pre-existing topographical context ...... 11 6. Rights & Responsibilities ...... 12 6.1 The Lead Local Flood Authority (Somerset County Council) ...... 12 & 13 6.2 Environment Agency ...... 13 6.3 Highway Authority ...... 13 6.4 Landowners and residents ...... 13 6.5 Riparian Owner’s Responsibilities ...... 13 7. Drop-in metting 10 th November 2016 ...... 124 & 15 Conclusion ...... 146

Executive Summary

On 17 th June 2016 three residential properties, and St John the Baptist Church in Chilcompton, were internally flooded up to a depth of 80mm and the highway up to a depth of 600mm. The subsequent investigation detailed below identifies the contributory factors of this flooding event.

As the Lead Local Flood Authority (LLFA) Somerset County Council’s (SCC’s) Flood and Water Risk Management (FWRM) team have carried out site inspections and met with residents.

This document has been written after a number of additional site meetings with residents, landowners, and the review of the informative comments from submitted Flood Incident Reporting Forms.

Thank you to all those individuals who contributed to this report.

1. Introduction

Lead Local Flood Authority Duty to Investigate

Under the Flood and Water Management Act 2010, Somerset County Council (SCC) is designated as the Lead Local Flood Authority (LLFA) for Somerset. This Act sets out a number of responsibilities for the County Council with regard to flooding, including a duty to investigate flood events within its area as it deems necessary:

(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— (a) publish the results of its investigation, and (b) notify any relevant risk management authorities.

Section 19, Flood and Water Management Act 2010.

Somerset County Council deemed it necessary to complete and publish an investigation into the flood event originating at the The Street and The Pitchings, Chilcompton on the17 th June 2016 as the event affected a significant number of properties and resulted in much correspondence and local concern.

This report provides a summary of the event and probable causes. It records the actions taken and/or proposed and the organisation or individuals responsible for completing them.

A ‘Risk Management Authority (RMA)’ means:

(a) the Environment Agency (EA), (b) a lead local flood authority, (c) a district council for an area for which there is no unitary authority, (d) an internal drainage board, (e) a water company, and (f) a highway authority.

When considering if it is necessary or appropriate to investigate a flood event Somerset County Council (SCC) will review the severity of the incident, the number of properties affected and the frequency of such an occurrence, and also other areas of particular concern. This incident saw four properties internally flooded and received many concerns from the community, as such the Lead Local Flood Authority (LLFA) SCC decided to investigate the event.

This report has been produced to comply with legislation and to determine the main causes of the flooding. It should be noted that in order to progress with their flood risk management function SCC has opted to develop this report further by considering the various actions that should be considered by the relevant RMAs. SCC as the LLFA will continue to monitor the list of actions with all of the RMAs and will assist in the delivery where practical to do so.

Each affected area or group of smaller areas investigated within this report will have a number of recommended actions to be taken forward by the relevant RMAs or in some cases, by the landowner or local community action group. There are various levels of action that can be taken depending on the severity of the situation and the practical solutions available to reduce the risk of further flooding. The recommended actions will generally fall into one of the following categories:

Delivery of Quick win schemes: a solution that can be implemented quickly by the Risk Management Authorities or Local Authority at relatively low cost. Further investigation/research: Further investigations such as catchment studies and hydrological/hydraulic assessments to understand the flow rates and directional paths and evaluate the extent of flooding. These would provide evidence for future capital investment. Development of Future schemes: Where immediate action is not financially viable or a solution not readily available then a larger scale flood alleviation scheme may be required. In such cases national funding would need to be secured together with additional contributions from others, such as local levy, local authorities and other third parties. Land owner action: Members of the public who own land adjacent to watercourses have riparian responsibilities and therefore have a duty to maintain their section of watercourse to ensure there is no impediment of flow. Other works to protect their property may also need to be funded by themselves to ensure delivery within their timescales. Community action: In some cases it may be prudent for community groups to join forces and deliver and maintain their own local schemes. In some cases this may generate further contributions from local levy or the LLFA.

This investigation report will provide a starting point, with suggested actions being further refined in the light of further studies and where possible, through further dialog with the affected communities.

2. Risk Management Authority Responsibilities

2.1. Recording Flood Incidents

2.2. Key Responsibilities

Risk Management Authorities (RMAs) in Somerset all have their own roles and responsibilities. The following Table 2.2 summarises the relevant flood risk management functions for each of the RMAs and the different sources of flood risk that the SCC investigation procedure follows.

Table 2.2 Relevant flood Risk Management Authorities that will take the lead in managing the risk from various local sources of flooding.

Flood Source Environment Lead Local Flood District Council Water Highway Agency Authority Company Authority (Somerset County Council) Rivers: Main river x Ordinary x x watercourse Surface

Runoff: Surface water x Surface water origination on x the highway Other: Sewer flooding x The Sea x Groundwater x Reservoirs x

3. Flood Incident Summary and Impact

3.1. Site Location

The catchment area covered by the investigation includes consideration of the farmland surrounding Chilcompton and the highway drainage system.

Flood investigation study area

Figure 1 – Parsonage Lane, The Street, The Pitchings, and Church Lane

Figure 2 – Broadmead, Parsonage Lane, and Greenditch Close

Figure 3 – Contour lines of Chilcompton highest point 180m AMSL and the lowest point 120m AMSL

3.2. Site characteristics and drainage

Chilcompton village centre sits at approximately ( ≅) 167m AMSL (Above Mean Sea Level).1 The Street at the junction with The Pitching Path sits at ≅ 130m AMSL whilst the Broadmead/Parsonage Lane junction sits at a height of ≅180m AMSL, therefore, a drop of up to ≅ 50m over 1.2km, a gradient of ≅ 4%.2

The indicative standard of flood protection for Chilcompton in 2004 was assessed as having a return period (the chance of flooding) of 1 in 5 to 1 in 50 years. 3, 4 This can be compared with the current standard guidance for developers of new housing developments requiring exceeding a return period of 1 in 100 year + 40% flood protection.5, 6

1 http://uk.storm247.com/ 2 LLFA’s MapInfo database in conjunction with Flood Map : Water Level Elevation Map at http://www.floodmap.net/ 3 DEFRA’s Project Appraisal Guidance (PAG) 3

4 Environment Agency, (July 2004), Chilcompton Pre-Feasibility Report, para 3.1.2, page 8. 5 The additional 40% takes in to account the effects of climate change.

6 Guidance in accordance with the Environment Agency’s Standard Guidance for Developers 6

There were two focal points highlighted by received Flood Incident Report forms to the flooding event on the 17 th June 2016 in Chilcompton. The first was on Broadway and Greenditch Close to the south of the village, where only the highway flooded with no internal flooding to properties. The second was on The Street outside the property known as Shell House, The Pitching Path and Church lane, where three residential properties and St John the Baptist Church suffered internal flooding.

The River Somer’s source is located at Old Down in the Mendip Hills. The River Somer is formed from a series of springs on the western side of Chilcompton, the river flows approximately 2km through rural land before reaching Chilcompton before flowing in a north easterly direction to Midsomer Norton. The river is classed as an ordinary watercourse up to the inlet of the culvert running east to west under The Street, between the properties known as Church House and Waterloo Farm through to The Pitching Path, and on toward Church Lane. The river from this point, the culvert inlet, and downstream is categorised as a Main River.7

Chilcompton and its surrounding area have a varied soil distribution. The village itself mainly sits on slightly acid loamy and clayey soils; this type of soil impedes drainage. To the south of Chilcompton lies freely draining slightly acid loamy soil; and to the west of Chilcompton Shallow lies lime-rich soils over chalk or limestone.8

Chilcompton’s highway drainage system, like all highway drainage systems, is programmed for cleaning according to whether they are high or low risk. The frequency of planned gully cleansing will depend on location (classification of road) and the relative risk of flooding. 9

• Gullies in flood susceptible areas will be cleaned every year. • Gullies in rural non-flood susceptible areas will be cleaned every two years. • Gullies in urban non-flood susceptible areas will be cleaned every four years.

The highway drainage in Parsonage Lane and The Street are programmed for annual gully cleansing, both were last cleaned on 05/04/2016. Broadway also had its gullies cleaned on the same date. All three were also cleaned on 14/05/15.

7 Refer to Table 2.2 on page 4 Risk Management Authority Responsibilities 8 http://www.landis.org.uk/soilscapes/ 9 Based on Environment Agency 1 in 200 yr deep FMfSW maps and historic data on flooding collated from Parish reports, Parish surveys, media reports, service requests contained on the highway maintenance management system and local knowledge. 7

4. Drainage and Flood History

4.1. Previous Flood Incidents 10

The areas of The Street, The Pitching Path and Church Lane are all within the Environment Agency’s Flood Zone 3 – High probability of flooding. And Chilcompton has suffered several flooding events in the past.

Historical flooding (known):

a) June 1968 b) 1972 c) 1985 d) 1987 e) 23 rd November 2009 – no properties flooded. f) St John the Baptist Church has suffered flooding in the past, however, this flooding was due to run off from the hillside located to the west of the church.

And, the latest occurrence:

g) 17 th June 2016 four properties flooded internally were reported to the LLFA. Note- One property’s kitchen flooded to a depth of 600mm and the rest of the property flooded to a depth of 300mm. The property owners have had to move out of their home and are not expected to return for up to 7 months whilst drying out and repairs are completed.11

10 Includes information from Environment Agency, (July 2004), Chilcompton Pre-Feasibility Report, para 2.4, pg 6 & 7 11 Information supplied at Drop-in Meeting held on 10/11/16. 8

4.2. Flood incident of 17 th July 2016

4.2.1. During the flood incident surface run-off water from the catchment area, including Lynch Hill, travelled via the B3139 Emborough to Chilcompton Road, Parsonage Lane and The Street and travelled to the lowest point on The Street. 4.2.2. Rainfall of 42mm over the 6 days preceding the flood event followed by the 44.6mm rainfall between 15:00 and 17:00 on the 17 th June and the consequential high volumes of surface water run-off from the large catchment area, ultimately increased the volume of water in the River Somer to such an extent, that it breached its banks adjacent to the public footpath known as The Pitching. In addition the volume of water overwhelmed the highway drainage system. 4.2.3 . The highway drains in The Street approximately 40m north of The Street’s junction with Parsonage Lane surcharged and began to flood The Street.

4.3. Rainfall Analysis 12

Rainfall data in the days leading up to the flooding has been obtained from the Environment Agency’s Chilcompton rain gauge. a) The average rainfall for the month of June since 1961 is 72.27 mm. b) The total monthly rainfall for June 2016 was 140.7mm . This is almost 2 times above the average June rainfall (72.3mm) since 1961 . c) The Rainfall from the 10 th June 2016 to 16 th June 2016 was 42mm (30% of June 2016’s total rainfall) this would have saturated the clayey soil prior to the exceptional rainfall of 44.6mm on the 17 th June 2016. d) The Rainfall on the 17 th June 2016 was 44.6mm (31.7% of June 2016’s total rainfall) and was falling on saturated clayey soil. e) The total rainfall from the 10 th June to 17 th June 2016 = 86.6mm i.e. 61.7% of June 2016’s total rainfall fell in one week. (This equates to 119% of June’s average rainfall since 1961 in just 7 days ).

12 Data supplied by the Environment Agency 10

5. Probable Causes

The investigation into this flood event has involved a number of organisations and the cooperation of the residents of Chilcompton and has considered a number of potential causes and contributory factors. Based on the investigation the following is considered contributory to the cause of the flood event on the 17 th June 2016.

5.1. Heavy rainfall in a relatively short period of time 13 The 42mm rainfall in the period 10 th -16 th June leading up to the flooding is 9 times greater than the average daily rainfall for June, and, almost 30% of the month of June’s average rainfall since 1961.

Average rainfall for June (since 1961) = 72.27mm Average No. of days that rain fell in June = 16 (including the 6 days leading up to the flood event) Average daily rainfall for June since 1961 = 2.6mm Average daily rainfall for June 2016 = 4.6mm Daily rainfall for 17 th June 2016 = 44.6mm

The average daily rainfall for June 2016 is 1.7 times greater than the average daily rainfall for June since 1961. And, that the 44.6 rainfall on the 17 th June was: • Almost 10 times greater than the average daily rainfall for June 2016. • 17 times greater than the average daily rainfall for June since 1961.

The data collected from the Environment Agency’s rain gauge clearly shows that this flood event was exceptional.

5.2. Housing within the pre-existing topographical context The properties that have reported internal flooding are within the Environment Agency’s Flood Zone 3, or, high risk area. The area being investigated has a history of flooding. This data and information is in the public domain.

13 Figures drawn from data supplied by the Environment Agency 11

6. Rights & Responsibilities

6.1 The Lead Local Flood Authority (Somerset County Council) In accordance with the Flood & Water Management Act 2010 upon becoming aware of a flood event the Lead Local Flood Authority must, to the extent that it considers it necessary or appropriate, carry out an investigation and publish the results notifying any relevant risk management authorities of its findings. Under the Land Drainage Act 1991 SCC have permissive powers to require works for the removal of obstructions to maintain the flow of any ordinary watercourse. In particular the LLFA have responsibility for ordinary watercourses 14 , and surface water and ground water flooding.

Findings & Actions

6.1.1 Initial SCC Site Visit 20/07/16 – Met with residents from Chilcompton and Ston Easton. Initial visit was primarily an information gathering exercise including walking the affected areas. The process of the Flood and Water Management team’s Section 19 Flood Investigation was explained, as was our jurisdiction and permissive powers. Considerable time was spent explaining highway drains and gullies, in particular the gullies approximately 40m north of The Street’s junction with Parsonage Lane, and the community’s expectations of these assets in relation to their functional limits and purpose. Property Level Protection (PLP) was discussed. Expectations of the probability of scheme funding were discussed in the context of the economic climate.

Action:

• SCC’s FRM team –

o Distributed Flood Incident Report Forms to affected property owners. o Ensured owner of Eagle House arranged for large obstruction in watercourse to be removed. o Sent letter of advice regarding collapsing wall directly adjacent to watercourse to the property owner of Moorlands. o Carried out a separate site visit of Green Street, Ston Easton. o Liaison with Mendip Area Highways.

6.1.2 SCC Site Visit 18/08/16 – The site visit focused on the watercourse downstream of the watercourse downstream of the culvert flowing under The Street. 15 The property owner of Mill Cottage explained the issues of surface run off from the fields to the west of Mill Cottage, Mill Farm and St John the Baptist Church. A further visit of Ston Easton was also undertaken.

14 Ordinary watercourses include every river, stream, ditch, drain, cut, dyke, sluice, sewer (other than a public sewer) and passage through which water flows and which does not form part of a main river. 15 Note this section of the watercourse 12

Action:

• Information gathering. An assessment of the surrounding agricultural land showed no obvious signs of any agricultural practices that would have compounded the flooding on the 17 th June 2016.

6.1.3 Communications with Parish Clerk – Request for Public Meeting.

Action:

A Drop-in Meeting has been arranged for the community on Thursday 10th November 2016 from 16:00 – 19:00. The following agencies/stakeholders will be in attendance: o SCC’s Flood and Water Risk Management Team o SCC’s Mendip Area Highways o SCC’s Civil Contingencies Unit o Environment Agency

6.2 Environment Agency – The Environment Agency carries out maintenance, improvement or construction work on main rivers to manage flood risk. A main river is defined as a watercourse marked as such on a main river map, and can include any structure or appliance for controlling or regulating the flow of water in, into or out of a main river. The River Somer becomes a main river from the inlet to the culvert running under The Street.

6.3 Highway Authority - Somerset County Council, as Highway Authority, is responsible for maintaining the highway. Highway drainage is designed to manage the rainfall upon the highway. These systems are not designed to manage excessive run-off from third-party land or from watercourses. The highway drainage is maintained in accordance with risk management principles, where areas susceptible to surface water flooding are maintained on an increased frequency compared with low risk areas.

6.4 Landowners and residents – Options to further address this flood risk will be considered as detailed above, however it should be recognised that homeowners have an important responsibility in protecting their properties.

It is recommended that residents be supported in developing a Flood Action Plan for their community to mitigate the impacts and reduce the time taken to recover should further flooding occur.

In addition it is recommended that homeowners consider steps that can be taken to protect their homes and that they are offered advice on property level flood protection products, suppliers and potential sources of supplementary funding.

6.5 Riparian Owner’s Responsibilities:

• Under common law landowners are the riparian owner of any watercourse within or adjacent to the boundary of their property • Where a watercourse is sited between properties each owner may be equally responsible • Riparian owners’ (landowners whose land is crossed or bordered by a watercourse) responsibilities include the maintenance of the bank and bed of their section of watercourse to prevent any obstruction to the flow in the watercourse. • Common failings include failing to keep vegetation under control and failing to obtain consent for installing pipes or culverts or undertaking other work that may affect the watercourse. • Riparian owners also have the responsibility to protect themselves and their property from flooding.

7. Drop-in Meeting 10 th November 2016

The LLFA’s Flood & Water Risk Management Team along with SCC’s Area Highway Office, and the Environment Agency attended a Drop-in Meeting arranged by the Parish Council for the community to address their concerns and comment on this report.

The main points from the Drop-in Meeting were as follows:

1. Many attendees commented on the drains and gullies in Chilcompton in particular Fry’s Well (including under the old railway bridge), Greenditch, and Stockhill Road and the large amounts of surface water. The comments included “the gullies are blocked”, “the gullies are never cleaned”, and the drainage system does not have the capacity to deal with the surface run-off.

Action: SCC’s Area Highways Service Manager for Mendip has arranged for Highway Inspectors to visit the various sites and engage with residents on to address these issues and see if a solution can be achieved. With regard to surface water run-off and capacity the highway drainage system is only designed to take the water that falls directly on to the highway’s curtilage, it is not designed to take surface water run-off from agricultural and rural land or private properties (please see para 6.5, pg13). It was also explained that to re-size the complete drainage infrastructure system would be cost prohibitive and wholly impractical on engineering grounds.

2. Councillor Christine Foster brought up the issue of planned works on two culverts.

Action: The works will affect two structures in Church Lane; School Culvert and Manor Farm Culvert and one other, Chilcompton Wood just outside the village on The Street. The works include shotcreting 16 the masonry arch

16 Shotcrete is concrete (or sometimes mortar) conveyed through a hose and pneumatically projected at high velocity onto a surface, as a construction technique. It is reinforced by conventional steel rods, steel mesh, and/or fibers. Fiber reinforcement (steel or synthetic) is also used for stabilization in applications such as slopes or tunneling. 14

structures to repair and reinforce them as well as carrying out localised repairs to the head walls etc. each culvert is anticipated to take five days. Disruption to the residents will be kept to a minimum with the only probable road closure and diversion being at School Culvert, this may be necessary due to the restricted area and pumping equipment that will be used to over pump the River Somer and apply the shotcrete, however the Contractor carrying out the works will be encouraged to liaise with local landowners in the immediate area with a view to siting such equipment on their land. It is hoped the works will be completed before Christmas; however a Jan/Feb completion date is more likely.

3. A number of attendees commented on the issue of run-off from new housing developments.

Action: A. Lambart of the SCC’s FWRM Team explained that SCC, as the LLFA, are consulted on planning applications of ten or more properties, site areas greater than 1ha and commercial developments greater than1 Hectare. (Schedule 4 of the Town and Country Planning (development management procedures) (England) order 2015). This came into force in April 2015 and made the LLFA a statutory consultee. As a consultee the LLFA can only advise and offer responses such as ‘Request for further Information’, ‘No Objection’, ‘No Objection with requests for conditions to be applied should the application be approved’, or Objection’. (If the LLFA raises an objection it must be legally supported by fact and the LLFA must be able to support this objection with fact at an appeal should the application be refused and the applicant subsequently appeals). The LLFA has no authority to impose a directive on the Local Planning Authority (LPA) (in this instance Mendip District Council). Residents were advised to voice their concerns and approach the LPA directly and preferably via the Parish Council.

4. Strategy for future heavy rainfall events

Action: A. Lambart contacted the SCC’s Civil Contingencies Unit (CCU) to liaise with the EA and the Parish Council to put a Flood Action Plan in place.

Conclusion

The investigation and the data within this report clearly indicate that the flooding event on the 17 th June 2016 was caused by an exceptional flash flood in which heavy rain fell over a very short period of time on to previously saturated soil. Historical data and evidence of previous flooding undoubtedly identifies that the properties that suffered internal flooding are in a Flood Zone 3 area, and therefore having a high probability of flooding as identified by the Environment Agency’s Flood Map for Planning.

This investigation also concludes that the highway drainage system has been maintained appropriately; and was only a contributory factor in that the system was overwhelmed by way of a combination of increased volume of water outside the highways design capabilities and curtilage.

The LLFA, Area Highways, and the Environment Agency will hold a Drop-in Meeting for the community to come and ask questions about the flood event and the investigation’s findings. The LLFA’s Civil Contingencies Unit will work with the Parish Council and community to put in place a Flood Action Plan.

An inspection of the watercourse showed no overall issues of concern related to the maintenance of the ordinary watercourse. There was however one small section that required the removal of a build-up of stones and debris caused by the force of the flow of water on the 17 th June. The riparian owner has organised for this obstruction to be removed.

As the flood event was an unfortunate and exceptional act of nature, i.e. a flash flood, it is logical to also conclude that any achievable flood alleviation scheme would not be able to mitigate such an event.

However, there may be an opportunity for the LLFA to carry out Property Level Resilience (PLR) assessments of the properties that were flooded internally. From there the LLFA can explore avenues for any PLP solutions identified and funding for PLP in the 2017/18 financial year.