Flooding Update

The Parish Council has been liaising with Anglian Water and other agencies following the flooding in the village at the Start of the year. Below are the questions raised so far and the answers given.

Response to follow up questions following meeting – received 12th May 2021

Drainage System – Please confirm that the Willingham drainage system is a combined system, ie, the foul wastewater and surface water are conveyed by the same pipes.

 The map we have shared indicates which parts of the network are foul only and combined. In some areas there are separate foul and surface water sewers. In the other areas where we only have a foul sewer system, there may be private surface water drainage systems or highway drainage systems which we do not own.  It is likely in the older of these areas, that over the years surface water sewer connections have been made to the local private or transferred drainage systems and hence into our main sewers.  This has the effect of turning the main sewer into a combined drainage system.

Overflows – What overflow provision has been incorporated within the combined sewer system to prevent the system from being overwhelmed during periods of exceptionally heavy and prolonged rainfall?

 There are no known overflows in the system.

Drainage improvements –  What major works have been undertaken by Anglian Water since adoption of the Willingham sewer system to maintain reliability, increase capacity and improve efficiency? Please provide scope of works and dates completed.

We have completed work at the local pump station including installing new/more efficient pumps, installing variable speed drives, new electrical panels and new airlines installed. As discussed in our meeting, we are continuing investigation to understand what mitigations need to be put in place in the network.

Infiltration –  Can Anglian Water give any details on the extent of infiltration within the Willingham catchment? If it is considered to be appreciable, can you give details on how it can be removed.

Our investigations will show the extent of the infiltration. Removal will depend on how it is getting into our system. For example an open joint or hole which is allowing ground water to infiltrate into the sewer can be lined with a structural liner. Where land drainage may be connected this can be stoppered off and disconnected as the connection of land drainage to our system is illegal.  Where surface water is ingressing into our system via flooded areas manholes can be changed to sealed types or where road drainage gullies are connected they may be reconnected to a suitable surface water system.

Pumping Stations –  Can Anglian Water provide details on all the pumping stations  within the catchment, including the number of pumps in each station, any overflow facilities and the pumping capacity of each pump?

This is slightly more complex question, so we can ensure we provide the right information, please let me know what are you are hoping to gain from getting this information?  

Bourneys Manor/Covent Garden – Would it be possible for the Council to attend site when the ongoing work/inspections is carried out at the Bourneys Manor/Covent Garden locations. If so please notify us of the dates/times the work is scheduled.

We completed some tracing of the surface water system that isn’t owned by Anglian Water in Bourneys Manor Close and we plan to check if there are any illegal or cross connections into the Anglian Water owned foul system. This work is yet to be planned and will be based on resource availability. Please note that this work will be subject to change depending on emergency work so it will be difficult to confirm a date. If the council wish to carry their own survey out on the surface water system then they are free to do so as this is not Anglian Water owned.

Survey work – Please confirm the survey work that is being planned for Willingham, the timescale and your proposals for undertaking the work.

We have completed a survey and cleaned the High Street sewer from the junction of Bourneys Manor down to the cross roads and then down Over End to the pumping station. No structural faults were found. Infiltration surveys will take place in future months and will be prioritised against other communities impacted by flooding

Response to question as to what work was being done on the High Street 21st April 2021

We asked IWJS to investigate the sewers on Anglian Water’s behalf. The purpose of this operation is to clean the sewer (remove any unflushables/fats, oils grease etc) and to CCTV the sewer.

 IWJS will also be surveying the surface water drains in Bourneys Manor Close in the coming weeks. Please note, these drains are not owned by Anglian Water. We are surveying them to check if they are connected to our sewers and could be contributing to increased rainwater and surface water flow in the system.

Response to initial questions received on the 26th March 2021

Is it correct that mains drainage was first installed in Willingham in about 1965 using nine-inch (225 mm) pipes for the main foul and surface water sewers?

We are not aware of any old records that we have which date the sewerage system. The pumping station land registry shows that the pumping station was registered as Anglian Water 1974 but may have been in place before this date. Our records were provided by the local authority and at that time would have been paper but have since been transferred to electronic mapping around 1995.  The best estimate of the system install is mid to late 60’s.  The main sewers vary in size across the catchment from 150mm to 300mm.  We have a very limited number of surface water sewers in the catchment and those we have are linked to newer developments. Any systems which carry surface water are likely to be either highway drainage systems or private sewers and culverts.

What was the design capacity of the system as installed in 1965 in terms of population?

We would not have the design criteria for the system as it was designed, the design of drainage systems has changed significantly over the decades. They would have followed standard design guidance and would have made an assessment of the current / future population to be served. However as water consumption and use has changed over the years, any assumptions made in the 1960’s would not apply today.

Has this drainage system been upgraded since Anglia Water adopted the system in 1973 and if so, what changes have been made?

The drainage system was under ownership of the local authority until 1989, we would not have any details prior to this date. After 1989, we have completed a number of upgrades, although sadly the paper records are not easily searchable. Anglian Water own approximately 74,000km of sewers and over 6,500 pumping stations. Two significant projects that we undertook were pumping station upgrades in 1998 and 1999 totalling £86,000.

What is the current maximum flow capacity of the foul drainage system in terms of population based on current design criteria (not multiples of dry weather flow) and what spare capacity (if any) is available?

Unfortunately we wouldn’t be able to comment on this; the flow capacity is calculated based on predictive modelling tools which is based on a number of variables including depth, pipe gradient and diameter and velocity of flow. Other factors include domestic flow populations (e.g. number of people per property, amount of water that goes down their drain).

What proportion of properties have a separate sewer and surface water drainage system, and how many AW authorised surface water connections into the foul drainage system are there?

We wouldn’t have a record of this information, as, quite often, builders connect surface water pipes to the foul water system. However,  a search of our systems has indicated no applications to connect surface water into the public sewerage system, and we would not normally approve this if we were approached. We don’t own many surface water sewers in the area, and until 2011 were only responsible for the main sewers. Property owners and builders may have connected surface water to their own private foul sewer without our knowledge.

What is the impact of these connections on the flow capacity of the current foul drainage system in times of heavy rain or local flooding, which are likely to be more frequent?

Without knowing the extent of direct surface water connections into the foul sewerage network, it is difficult to assess the impact of any connections. However, we are confident that the system does have capacity for all known new connections.

How many properties currently have a Surface Water Drainage discount?

Unfortunately we are not able to find this out for the whole village, as individual customers can apply for this discount for their properties and is therefore a private billing matter.

Does the current system have storm overflows?


Are drainage flow rates flows monitored either manually or remotely and records kept?

Drainage flows are not monitored through remote sensors in the network. We do monitor flow into local pumping stations.

Are there any ‘pinch points’ or locations where the flow is being restricted? If so, what are your plans to permanently rectify these?

There are no locations in the sewer network where flows are being restricted.

Could the Parish Council be provided with an up to date copy of the layout plans showing the complete drainage system in the village including where surface water is allowed to enter the foul sewer system and storm overflows?

We will look into obtaining some maps of Anglian Water’s assets in the village, and share in due course.

Is there a planned maintenance programme for pumps, valves and pipework installed in the Willingham drainage system and if so when was the last inspection undertaken and can AW provide an overview of the recommendations?

The local pumping station is on a predictive dynamic maintenance service program. The pumping station service was carried out in April 2018 when it was on a 18 monthly routine. In predictive dynamic maintenance service programs, live data from pumps will identify any insufficiencies for service and maintenance or repair. We carried out work at the station in August and September 2020 where we inspected the pumps, installed airlines and reviewed the control panel with adjustments. We also performed a wet well clean and are aiming to undertake an Infiltration Reduction Plan over the coming months and can share the findings when complete, as laid out in the points mentioned in the next question response below.

Are there any plans to upgrade the current foul drainage infrastructure and if so, what changes are proposed and when are these planned to be funded and implemented?

We will be completing investigations as a result of the wet weather incident, please see our methodology below:

The first stage is to understand the root causes that have led to these flooding events. In some cases asset maintenance or condition may have contributed to flooding (such as a defect in a sewer leading to infiltration, a blockage of highway drainage or a reduced capacity of a watercourse) whereas in other cases the inundation caused by the extreme wet weather event will have simply been beyond the capacity that the drainage system was designed to cope with. Whilst much of the evidence to support these investigations was gathered during the flooding event; we expect to begin thorough analysis of this information in the next few months. This will be used to inform our ongoing investment prioritisation process.

If evidence suggests that below-ground infiltration into an Anglian Water sewer contributed to the flooding, these assets can be examined using CCTV and flow monitoring to determine the location of any defects. These investigations can only be completed when water levels within the system have receded. If a defect is identified, this work would then need to be prioritised alongside other maintenance activities across Anglian Water, hopefully to be delivered later this year.

If evidence suggests flooding is the result of a capacity issue of an Anglian Water asset, then opportunities to increase the resilience of that asset would be reviewed. Initially we would investigate mitigation options (for example non return valves to protect properties) before investigating and prioritising enhancements to existing systems, such as SuDs solution, re-routing sewers, or installing additional capacity.

If evidence suggests that flooding is the result of a third party asset (either fully or partially) then Anglian Water would seek to work with those parties to resolve the issue. Often surface water related flooding is best addressed with a multi-agency response, and Anglian Water very much supports this approach and we are always willing to work with other stakeholders to address flooding issues. It is a complex problem, as there is no one agency responsible for surface water management, so real action can only succeed with multiple parties working together.

What is the depreciation policy for fixed assets such as pumps, valves and pipework and is replacement planned against life expectancy?

We do have a capital depreciation policy for new assets, however, our replacement schedule is based on performance, any failures and measured against other assets in the network. Our funding is very carefully controlled through the independent economic regulator, OfWat, and as such there is a very robust process for all capital investment.

We have reports of poor response to complaints. Are there any plans to improve response times and customer relations?

Sadly, we had to manage complaints and call-out differently due to the widespread wet weather incident and the increased contact this caused. Our team handled unprecedented volumes of contacts from people affected, often looking for advice and guidance on where to turn – more than 30,000 jobs raised in direct response to flooding with 80,000 incoming calls; around 5 months’ worth of incoming work in just seven weeks.

Would Anglian Water put a system in place whereby the Parish Council are kept informed of both maintenance and infrastructure improvements as well as notifying us of issues that arise that may affect multiple dwellings?

We will keep the community informed where we complete work which would affect them or might result in disruption. Additionally, individuals can sign up to alerts from In Your Area: https://inyourarea.digdat.co.uk/anglianwater

Initial response from Anglian Water on the 8th February 2021 following complaint

The initial problem at Church Street was the result of a blockage which was cleared, but I’m sorry to hear about further problems in the village.

 The current situation is unfortunately down to the extreme rainfall we’ve had since Christmas and the very high water table and rivers and streams overtopping.  This results in our systems becoming inundated with surface water.  Whilst we can use tankers and direct pumping to remove some of this flooding, in some locations it is simply not viable due to the sheer volume of water we are dealing with and we look to other agencies for support, particularly the Local Resilience Forum.

 I’m told that we are continuing to deploy tankers at Bourneys Close to help customers and are considering further options to provide assistance if we can, including direct pumping if this is feasible.

 With regards to the flooding on the Green, our area supervisor attended on 3rd February and reported that the area is clear – if this is not the case, then do please let me know.

 I am sorry that there are still residents who are experiencing loss of facilities.  As the system continues to drain down from flood water and as the water table continues to reduce, this will improve.  In the meantime, we encourage residents to continue reporting loss of facilities directly to us so we can track these and continue reporting to the Tactical Coordination Group and the Local Resilience Forum.

 Once the water recedes we will be in a position to carry out detailed investigation, along with other flood risk partners, to understand the cause of flooding and what can be done to alleviate the impact on residents, which we will be happy to share with you.  This will include full CCTV survey of our sewers to check for blockages, and further assessment and any necessary work at our pumping station.  Once this is complete we can see if any further engineering work is required on our network.