29 January 2019

A report has been published into the flooding which happened in St Leonard’s Road, Northampton, earlier this year to find out how it happened and what can be learnt.

The report – which was carried out independently by David Smith Associates – was commissioned by Northamptonshire County Council as the lead local flood authority (LLFA).

The surface water flooding on 27 May, 2018 was caused by intense heavy rainfall, which was experienced throughout south Northampton and also in Buckinghamshire and the West Midlands.

Rainfall data for the incident indicates that up to 93mm of rain may have fallen in just one hour in Wootton, compared to the monthly May average of 54mm.

The report states that the rainfall was beyond the design capacity of drainage systems across the St Leonard’s Road catchment area. This combined with the geography of the St Leonard’s Road area, which is situated in a localised bowl, led to excess surface water – up to 90cm deep in some places. The investigation identified that 70 properties on St Leonard’s Road were flooded internally and many more affected by the flooding.

It was reported that bags of refuse and loose litter, left outside properties for collection the following day, were moved by flood water to cover some road gullies and prevent them from draining flood water. Once these were removed water receded more quickly.

The investigation also revealed that whilst some drainage systems were reported to need maintenance and cleansing prior to the flooding incident, this was not the difference between the flood event occurring or not occurring.

Cllr Ian Morris, county council cabinet member for transport, highways and environment, said:

 

“Whenever there is an incident of this severity and impact it’s essential that a full investigation is carried out to find out exactly how it happened.

“This is important so that lessons can be learned to try and minimise the risk of this sort of thing happening again.

“What we have discovered here though is that this was a freak storm that deposited up to twice the monthly rainfall over the period of one hour and very little, if anything, could have been done to prevent it.

“However we will take heed of any recommendations as I’m sure our fellow partners will and work collaboratively to minimise the risk of flooding.”

The Met Office issued an amber warning for thunderstorms on Sunday night, however Northamptonshire was only on the extremities of the warning area, and it did not extend to Northampton itself. Additionally there were no community or property level resilience measures in place that could have been deployed.

There was a co-ordinated recovery response from emergency services, local authorities and other flood risk management authorities, including the Environment Agency and Anglian Water.

Flood investigation reports for other affected areas in Northampton will be published in the coming weeks.

Key Recommendations from the report

The suggestion that the LLFA coordinate with other flood risk management authorities to extend publicity of the existing information available in relation to flood risk on the Flood Toolkit website and consider further means to publicise this information to specific communities at risk of flooding.

That the LLFA should work with the community and risk management authorities to assess the viability of options for engineering schemes to reduce flood risk. This might include community level flood resilience measures, improving drainage to accommodate extreme rainfall events, providing attenuation storage areas and creating formal overland flood flow routes.

That local authorities, emergency services and other relevant response groups should continue to work together, and review their immediate and follow up response to the emergency.

Further recommendations include that owners of affected properties should consider preparing a household emergency plan or business continuity plan, and implementing property level resilience.

And that with support from flood risk management authorities, the community should make efforts to:

  • Appoint community flood wardens
  • Prepare a community emergency plan
  • Explore options for funding and contributions for schemes to manage surface water and flood risk.