A Flood of Claims: How an Expert Witness helps determine liability


By Richard Allitt Associates- Expert Witness Services for all Flood & Drainage related issues

Flooding and its impact on property such as homes, businesses and agricultural land continues to grow in importance. Already there are an estimated five million people living in 2 million properties located within flood risk areas in England & Wales.

Why is there a rising tide of flooding claims?

The flood damage for the winter of 2013/14 has been estimated at over £500m, with insurers receiving more than 174,000 claims between 23 December 2013 and 8 January 2014 alone. Whilst historically there was little hope for recovery from flooding claims, the increased incidence and large sums involved has caused the industry to be more inclined towards recovery.  Necessarily, as the economic cost of flood events continues to rise there has been an accompanying rise in those seeking to apportion costs. These claims are both from those directly affected as well as from insurance companies and other third parties. Inevitably the legal process has to determine liability in such cases, making it increasingly important to understand how liability for flooding might arise.

 How can an expert witness help in these cases?

A legal case arises when flooding causes damage to property, land or belongings and there is considered to be fault attributable for the associated costs. The purpose of bringing in an expert witness is to provide not only a subjective opinion based on in-depth flooding specific experience but also to provide some objective science which is based on observable phenomena which can be presented factually. Indeed the credibility of an expert witness’ testimony is largely based on their ability to have a sound objective opinion.

So what scientific tools does the expert employ?

The basis of the scientific information used by an expert in flooding cases is called hydraulic modelling. It is an important software tool for any flood & drainage related expert witness work. Hydraulic modelling when used by a flooding expert witness can help determine who if anyone is liable. In essence a hydraulic model works by taking all the relevant known information about the flooding incident and using this to model predicted outcomes. Essentially the model will look at a set of circumstances incorporating factors such as:

  • Rainfall
  • Tides
  • Ground wetness
  • Infrastructure such as screens
  • Controls
  • Valves

Importantly the models can also be used to predict the pattern of flooding over time, indicating if remedial action could have minimised damage for example. It is a decidedly skilful process demanding considerable experience and training to know which variables to enter into the modelling software and determine which scenarios are the most likely.

The models can be used for looking at flooding from a variety of different sources such as ponds, rivers, reservoirs as well as from sewers and culverts. It is possible to observe the implications of blockages in outlet pipes and of screens. Whatever cause the claimant thinks is at the root of the flooding incident can be fully tested and modelled to establish whether this was the case. By using their in depth knowledge of the industry and hydraulic modelling techniques the expert witness can provide the legal team with objective scientific information that can clearly determine what has occurred and who is responsible.

Evaluating the Cost

By being able to look at a range of different scenarios the expert witness is also able to quantify the extent of the liability involved. By using hydraulic modelling it is possible to model what the situation would have been if a particular action which caused the flooding incident such as erecting railings or closing a valve had not been done. In this way it is possible to precisely measure the cost difference between what actually happened and what would have been the situation otherwise. This is an extremely useful way of quantifying the incremental costs of damage.

Do you always need an expert in flooding cases?

In straightforward cases where the cause is clearly observable it may not always be necessary to employ a hydraulic modeller. However where more data is required and cause is not clear then the modeller should be highly skilled and experienced in order to understand all the possible scenarios. The modelling software helps the expert to address a wide variety of ‘what if’ questions and can be used to test a variety of alternative hypotheses. There is no doubt that employing a skilled flooding expert will result in well-defined plans and visualisations which will enable everyone without specific knowledge of the industry to understand clearly what has occurred. The expert witness will in this case not just be a (albeit well informed) subjective opinion but be able to provide objective data to illustrate that opinion.

In flooding related matters the right expert witness can bring facts and clarity to facilitate the process of law.

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“Our aim is to resolve flooding problems in the urban environment using the latest analytical techniques”


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