Flood investigation reports

1.0 Introduction

1.1 Instructions

1.1.1 Martin Andrews Consulting Ltd (MAC) have been appointed by North Northamptonshire Council (NNC) to undertake a survey of properties located along the route of the East Brook Culvert (as understood) to establish the extent of any flooding along this culvert along with basic details of the incident.

1.2 What is the East Brook Culvert?

1.2.1 The East Brook Culvert is a buried watercourse which runs through Kettering beginning near Brambleside to the north of Kettering and continuing southwards until it becomes an open watercourse again at the allotments accessed off Spring Rise.

1.2.2 The route of the culvert, as best understood, is shown in Appendix A.

1.2.3 From a review of historical OS mapping the culverting of East Brook Culvert began between 1884 and 1899 and will have continued as Kettering expanded.

1.3 Survey methodology

1.3.1 NNC provided MAC with a plan which showed the route of the culvert, as they have been able to identify it, within Kettering. From this MAC identified 607 properties which are in some way adjacent to the culvert and may have been affected by flooding as a result. Drawings showing the houses which were included within the survey are enclosed in Appendix B.

1.3.2 A questionnaire was produced which was mostly hand delivered (others were posted) to all of the houses identified. This provided the resident with an opportunity to complete a paper survey to be returned by post or complete the form electronically. A copy of the questionnaire is included in Appendix C. We understand some residents may not have received a copy of the survey, however, best endeavours were undertaken to include all possibly affected properties across a large area with an unknown scope of impact. It is also noted that the local press published an article which included a link to the online survey.

1.3.3 The purpose of the survey was to identify where flooding had occurred and the approximate number of properties which had been flooded and the extent of this flooding.

1.3.4 The results of the survey will be used to inform any further work and to support bids for additional funding which may be need.

1.4 Mapped flood risk

1.4.1 The route of the culvert is located within Flood Zone 1 as per the Environment Agency’s Flood Map for Planning (Rivers and Sea). Extracts from the Environment Agency’s surface water flood risk map are shown below, see Figure 1.1 and Figure 1.2. This shows that the route of the culvert (indicated in red) is located predominantly in an area of high-risk surface water flooding. The high-risk category would fit with what is a local valley running through this area of Kettering, hence, the historical watercourse which has now been
buried.

Figure 1.1: Surface water flood risk map - extract 1

Figure 1.1: Surface water flood risk map - extract 2

2.0 Results of the Survey

2.1 How many responded?

2.1.1 Of the 607 surveys which were distributed 89 (15%) were returned of which 45 (7%) reported they had been flooded and 44 (7%) reported no flooding.

2.1.2 Of the 45 responses which responded yes to flooding, 25 reported internal and external flooding and 20 reported external flooding only.

2.1.3 Whilst the flooding is impactful based on the results of the survey a relatively small number of properties of those adjacent to the East Brook Culvert have been affected although of those affected some have been affected multiple times.

2.1.4 It is possible that not all flood incidents have been recorded for a number of reasons including a change of homeowner, however, the results included within this report represent the entirety of the survey responses received.

2.1.5 A summary table of all responses is included in Appendix D, this has been anonymised to remove house numbers and contact details.

2.2 Where did the flooding occur?

2.2.1 Of those that responded yes, the flood incidents occurred on the streets set out in Table 2.1:

Table 2.1: Location of flood incident

2.2.2 For anonymity purposes we have not provided a map to show the location of all respondents, however, whilst there have been flood incidents along the length of the culvert’s route the majority fall into three broad locations.

• Location 1: Kipling Road / Browing Avenue
  Whilst also affecting other streets this area at the head of the culvert in the north of Kettering reported 17 flood incidents or 38% of the total returned responses.
• Location 2: Byron Road
  Slightly south of location 1 there is a small cluster of 4 properties which flooded
• Location 3: Waverley Road / Boddington Road
  Whilst also affecting other streets this area at the downstream end of the culvert reported 11 flood incidents or 24% of the total returned responses. Waverley Road has been subjected to a previous S19 investigation by North Northamptonshire Council

2.2.3 The three locations are indicated in Appendix D and Figure 2.1, Figure 2.2, and Figure 2.3. Figure 2.2 below.

Figure 2.1: Location 1

Figure 2.2: Location 2

Figure 2.3: Location 2

2.3 When did the flooding occur?

2.3.1 Not all respondents to the survey provided date information or dates for all of the floods, however, a summary of the date details with the number of properties affected during each date window is summarised below in Table

2.2. Due to the historical nature of this assessment, dates of flood incidents are summarised by month or year only. On some occasions more than one significant rainfall event has occurred in any one month, hence, there will be a small amount of double counting of properties affecting by a single rainfall
event in some time periods.

Table 2.2 Date and number of incidents

2.3.2 Based on the survey responses the majority of flood incidents affected only a single dwelling although the further back in time the less accuracy there will be in this data as people move houses etc.

2.3.3 During 2022 and the first 8 months of 2023 there were 63 flood incidents with two particularly significant events affecting multiple properties in August 2022 (17 reports) and June 2023 (31 reports). For ease of reference the responses which include reference to flooding in either of these events are summarised in Appendices E and F respectively.

2.4 What might have caused the flooding?

2.4.1 The purpose of this survey was not to try and understand the full mechanisms behind each flood or even how they flooded, however, the survey did include a question to ascertain what the residents’ thought was behind the flooding. The responses are summarised below in Table 2.3.

Table 2.3: Residents reasons for flooding

2.4.2 The main reason cited for the flooding by residents affected was a lack of drainage capacity / maintenance of the drainage system.

2.4.3 At this stage further investigations into drainage capacity have not been undertaken.

2.5 How deep was the flooding?

2.5.1 The survey asked residents to estimate the depth of flooding during the worst event both internally and externally. They were asked to provide an estimate based on one one of four depth bands. The results of the survey are summarised below in Table 2.4.

Table 2.4: Estimate of flooding depth

2.5.2 Internally typical flood water depths were typically up to 150mm whilst external flooding depths tended to range from 150mm to 600mm.

3.0 Other Reports of Flooding

3.1.1 In addition to the survey we have reviewed information available within the public domain and reported directly to the LLFA to identify any other locations of flooding. The following addresses also have historical reports of flooding.

• Bath Road
• Cedar Road
• Willow Road

5.0 Conclusion

5.1 A survey of 607 properties located along the route of the East Brook Culvert was completed in August 2023. Of these 45 responded to say that they had experienced historical flooding of their property. Many of those affected by the flooding have been flooded multiple times.

5.2 The route of the East Brook Culvert lies in a natural valley as such is the located in an area with a high risk of surface water flooding.

5.3 Properties along the route have experienced flooding, however, there are three broad clusters around Kipling Road / Browing Avenue, Byron Road, and Waverley Road / Boddington Road.

5.4 From the responses we received flooding seems to have always occurred in some locations along the route of the culvert although there were two significant events which occurred in August 2022 and June 2023 with 16 and 31 reports of flooding.

Appendix A - Route of East Brook Culvert

Extend of Survey - Page 1 of 4

Appendix B - Extend of Residents Survey

Extend of Survey - page 2 of 4

Extend of Survey - page 3 of 4

Extend of Survey - page 4 of 4

Appendix C - Residents questionnaire

1. Address
2. Name (not mandatory)
3. Contact details (not mandatory)
   • Phone
4. Contact details (not mandatory)
   • Email
5. Has your property flooded from external sources? i.e not because of an internal plumbing failure
   • Yes
     • If yes please complete the below questions
   • No
   • If no please return the form. No further questions need to be provided.
6. How many times has your property flooded internally?
7. How many times has your property only flooded externally?
8. Can you provide approximate dates for the flooding?
9. What do you think caused the flooding?
10. Where did your property flood from? i.e front or back, if different each time please provide details.
11. How much of your property was affected?
12. Did you have to leave the house for more than 24 hours due to the flood incident(s)?
13. In the worst event approximately how deep was the flooding externally?
    • 0-150mm (0-6 inches)
    • 150-300mm (6-12 inches)
    • 300-600mm (12-24 inches)
    • greater than 600mm
14. In the worst event approximately how deep was the flooding internally?
    • 0-150mm (0-6 inches)
    • 150-300mm (6-12 inches)
    • 300-600mm (12-24 inches)
    • greater than 600mm

Appendix D - Summary of all survey responses

Appendix E - Summary of all August 2022 survey responses

Appendix F - Summary of all June 2023 survey responses

1.0 Introduction

1.1.1 Martin Andrews Consulting Ltd (MAC) have been appointed to undertake this Section 19 Flood Investigation on behalf of North Northamptonshire Council (NNC) for a flood incident which occurred on Rockingham Paddocks, Kettering. The properties had flooded more than once in the specified period so warranted an investigation.

1.1.2 This investigation was undertaken following an incident which occurred on 23 October 2022, with the previous and subsequent events occurring in June 2021, 20 October 2022, June 2023 and September 2023.

1.2 This document comprises an anonymised summary of the full Section 19 Flood Investigation for the publication.

2.0 Description of Investigation Area Catchment

2.1.1 The description below describes the catchment as understood to be relevant to the investigation.

2.1.2 Rockingham Paddocks comprises a metalled surface serving a number of residential dwellings. The carriageway falls from east to west towards Rockingham Road. The properties which flooded are downstream and to the north of Rockingham Paddocks. They are served off a shared driveway area where the carriageway edge of Rockingham Paddocks is defined by dished and bullnosed kerbs with the aim of directing water away from the two properties.

2.1.3 Rockingham Paddocks has two road gullies upstream of the flood incident. Both were observed to be blocked to some degree.

2.1.4 Ground levels on the shared driveways fall towards the two properties.   

3.0 Description of Flood Event

3.1.1 The flooding is based on descriptions taken from those affected during our site visit. All depths mentioned are an approximation based on the descriptions provided.

3.1.2 Upstream of the affected properties a rainfall event exceeded the capacity of the highway drainage. During the 2023 site visit two road gullies were found to be blocked to some degree and in their current state of maintenance would not have been operating at their expected performance level. As a result, surface water flowed down Rockingham Paddocks bypassing the dished kerb and followed natural flow routes towards Property 1 and Property 2 rather than continuing down Rockingham Paddocks towards Rockingham Road.

3.1.3 At Property 1 water entered the small courtyard area which has two doors and watered entered the property via these openings. Water reached depths of around 125mm externally and caused internal flooding.

3.1.4 Property 2 has an external stepped access into a basement. Water flowed down the steps and into the basement. External flooding reached depths of around 300mm deep outside the below ground access into the basement and then enters.

3.1.5 Residents did not leave either dwelling.

3.1.6 A plan of the flood incident showing the approximate location of the event and flow routes is enclosed in Appendix A.

4.0 Suspected Causes of the Flooding Event

4.1.1 In any flood incident there can be numerous factors which could have resulted in the flooded witnessed. From the information we have received these are the key factors:

• Poorly maintained private drainage caused overland flows along Rockingham Paddocks and ultimately into both properties. 

5.0 Recommendations

5.1.1 The road gullies are cleaned of all silt. An inspection of the drain (sewer) which serves the highway drainage may be required to confirm it is not blocked and operating effectively.

1.0 Introduction

1.1.1 Martin Andrews Consulting Ltd (MAC) have been appointed to undertake a Section 19 Flood Investigation on behalf of North Northamptonshire council (NNC) for a flood incident which occurred on Benefield Road, Oundle. The property had flooded twice in 2 years so warranted an investigation.

1.1.2 This investigation was undertaken following an incident which occurred on 18th June 2023, with the previous event occurring in July 2020.

1.2 This document comprises an ammonised summary of the full Section 19 Flood Investigation for the publication.

2.0 Description of investigation area catchment

2.1.1 From visual observation and videos of flooding Benefield Road in front of the properties appears to be broadly flat but has a fall from west to east. On the southern side of Benefield Road there is a footway which at its maximum is approximately 500-750mm lower than the carriageway. Although the depth varies from west to east with the maximum depth broadly by the affected property(ies). South of the footway is a row of terrace houses which include the flooded property which itself is approximately 150mm lower than the footway.

2.1.2 To the north the footway is of a standard arrangement. North of this and opposite the property is the Drill Hall car park which is managed by Oundle Town council. The car park is relatively steep falling from north to south towards Benefield Road and also but to a lesser extent falls from east to west towards the access point. On its southern boundary the car park is accessed via a crossover with a stonewall along the rest of the boundary.

3.0 Description of flood event

3.1.1 This section is based on descriptions taken from those affected during our site visit. All depths mentioned are an approximation based on the descriptions provided.

3.1.2 A similar flood occurred in July 2020 with broadly identical mechanisms. The event in 2020 caused more extensive damage than the 2023 event.

3.1.3 A significant rainfall event occurred during both events. During the event, rainwater ponds on Benefield Road in front on the impacted dwellings. The ponded water then overtops the retaining wall upstand either due its depth or due to cars splashing the water over the upstand. This water then ponds on the lower footway entering the affected property through the door and wall. Additionally, water is also seen flowing from the west along the existing fall in the footway towards the dwelling.

3.1.4 There are road gullies on Benefield Road in this location, however, these were unable to cope with the volume of water. There is also a linear drainage channel on the lower footway, this was also unable to cope with the water during this incident.

3.1.5 Video evidence seen during the investigation provided by the residents shows that there is water flowing off the Drill Hall car park on to the highway. As the Drill Hall car park is served by isolated gullies rather than a linear drain it is possible that this is a normal occurrence during an extreme rainfall event. Based on our observation and knowledge of drainage design we would expect water to flow off the car park during significant rainfall events regardless of the maintenance schedule of the Drill Hall car park drainage.

3.1.6 Whilst it was not mentioned by the resident it is noted that rainwater pipes from the terraced houses discharge directly onto the lowered footway. The significant rainfall event would have led to additional volumes of water, compared to a typical event, draining onto the footway which may have exceeded the capacity of the linear drainage without the addition of any water overtopping the upstand of the retaining wall.

3.1.7 Flooding has occurred as the highway drainage was unable to cope with the rainfall which was generated during the event. Additional water from the Drill Hall car park has increased the volume of the water on the highway but based on the historical drainage design used on the car park this would be expected to occur.

3.1.8 Since the 2023 event, the residents have installed a flood barrier to both external doors and use sandbags to prevent water flowing along the footway.

3.1.9 A plan showing the approximate extent of flooding and flow routes is enclosed in Appendix A.

4.0 Suspected cause(s) of the flooding event

4.1.1 In any flood incident there can be numerous factors which could have resulted in the flooded witnessed. From the information we have received these are the key factors:

• Excess rainfall exceeded the capacity of the drainage infrastructure resulting in flooding.
• Possible blockage of surface water drainage– although with the exception of possibly one Drill Hall car park gully there were no obvious signs of blocked inlets during the visit. The highway drainage is also maintained annually.
• Drainage arrangement on Drill Hall car park allows water to flow onto the highway. This will have increased the volume of water on the highway and exacerbated the inundation of the highway drainage beyond its designed capacity. It should be noted that the car park will have existed for many years and the drainage arrangement has not been altered recently.
• Rainwater pipes from properties directly discharge onto the lowered footway. The rainfall event may have overloaded the linear drain without the addition of highway water.

5.0 Recommendations

5.1.1 Drill Hall car park and highway drainage should be inspected to ensure there are no blockages or damage and it is able to operate at its designed capacity.

5.1.2 Consideration should be given to whether the Drill Hall car park drainage could be improved to reduce the volume of water which is discharged onto the carriageway.

5.1.3 Highway drainage on the lower footway to be inspected to ensure it is operating as expected to ensure that it has as much capacity as possible for flows from the rain water pipes and the footway.