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Flood Investigation Report process

As the Lead Local Flood Authority (LLFA), we are required to investigate significant flood incidents and produce Flood Investigation Reports under Section 19 of the Flood and Water Management Act 2010.  

We investigate flood incidents which meet Flood Investigation Thresholds.

Flood Investigation Thresholds

When a completed 'Report a Flood’ is received by us, the details will be reviewed to see if a formal investigation is needed. 

A formal flood investigation will generally be carried out if one or more of the following occurs:  

  • flooding has affected critical infrastructure* for a period in excess of three hours from the onset of flooding
  • internal flooding** of a building has been experienced on more than one occasion in the last five years
  • internal flooding of five buildings in close proximity*** has been experienced during one single flood incident

* Those infrastructure assets (physical or electronic) that are vital to the continued delivery and integrity of essential national services, the loss or compromise of which would lead to severe economic or social consequences, or to loss of life.  

** A situation in which a building (commercial or residential) has been flooded internally, i.e. water has crossed the threshold and entered the building. 

This includes:

  • basements and ground level floors of the building
  • garages/outbuildings if they are integral to the main occupied building - garages adjacent or separate from the main occupied building are not included  
  • occupied static caravans and park homes - tents are not included

*** Where it is reasonable to assume that the affected properties were flooded from the same source, or interaction of sources, of flooding.

Who the investigations are undertaken by

David Smith Associates, DSA, is a specialist engineering and construction company in the Northampton area. DSA is contracted by us to undertake the investigations.

What the investigation will cover 

The investigation includes an overview of the flooding incident and its impact, the drainage infrastructure in the wider catchment, any history of flooding, a rainfall analysis, and the roles and responsibilities of all involved. 

The report will also highlight a series of recommendations for all those involved, including residents and businesses.  

The investigation will:  

  • identify and explain the likely cause(s) of flooding
  • identify which authorities, communities and individuals have relevant flood risk management powers and responsibilities
  • provide recommendations for each of those authorities, communities and individuals
  • outline whether those authorities, communities or individuals have or will exercise their powers or responsibilities in response to the flooding incident

The investigation will not:  

  • resolve the flooding issues or provide designed solutions
  • force Risk Management Authorities (The Environment Agency, the LLFA, the relevant water company and highways authorities) to undertake any of the recommended actions
  • investigate incidents of structural dampness or where basements are affected by groundwater entering through cracks in the basement walls or floors
  • investigate an incident if it is reported after nine months of the flood event occurring

What happens if the cause of a flood incident is well understood

In the event that the cause of, and the responsibility for addressing the flooding is well understood, no formal investigation will be undertaken.  

The formal investigation process

Upon learning of a flood event within West Northamptonshire, the Investigating Officer (DSA) will follow the established ‘Flood Investigations Protocol’. Six steps will be used to determine whether an investigation should be carried out.

  1. 'Report a Flood’ form received.
  2. A review of the information provided to determine if the incident meets the threshold for formal investigation. If the incident does not meet the threshold, then advice and guidance is provided. 
  3. If the incident does meet the threshold, then a site meeting is arranged with the affected community and a data collection process is undertaken. This will include any photos, video footage and eyewitness statements.
  4. A draft Flood Investigation Report (FIR) is written and shared with all relevant Flood Risk Management Authorities (RMAs) for comment and review.
  5. Any necessary revisions are made to the FIR and the report is published online.
  6. All RMAs and the affected community are notified of the publication of the Flood Investigation Report.

Potential actions taken following an investigation

It is important to note that this is a technical assessment. It is for the relevant responsible body or persons to assess any recommendations in terms of their legal obligation, resource implications, priority and cost/benefit analysis of undertaking such recommendations.  

How long it will take

We will endeavour to undertake and complete a flood investigation report within six months of receipt of a flood incident report form. However, this may not be possible following extensive flooding when significant numbers of flooding are received.

Following significant widespread flooding in the county, where a number of incidents meet the thresholds for investigation, these will be undertaken on a priority basis based on:  

  • the type of flooding
  • the impact
  • what was affected  
  • the duration of flooding
  • whether or not major roads were impassable
  • whether the flood water was contaminated
  • the depth of the flood water
  • the number of times the flooding has occurred

Last updated 08 March 2024