Expert Witness, Richard Allitt BSc FICE CEng CEnv of Richard Allitt Associates explains the importance of a methodical approach in identifying the root causes of flooding in the latest issue of Expert Witness Magazine
With heavy rainfall and storms seen across the UK at the end of May, there will no doubt be a spate of flooding damage claims coming through in the near future.
In most flooding cases I am involved with, my instructions are to investigate the cause of the flood damage, considering all possible causes and where potential causes are excluded and to provide reasons why.
In many cases, what is initially perceived to be the cause of flooding is proven not to be the case upon detailed investigation.
It’s imperative to approach each case in a methodical and analytical way, with a site inspection being one of the first steps in data collection.
I often spend time with residents to discuss their experiences of how the flooding occurred, walking around the properties involved, the adjacent land and taking photographs. I also use RAA’s GPS survey equipment to take site measurements and levels. On larger sites and harder to access areas I make use of RAA’s own specialist Remote Aerial Survey service which uses UAV’s (Drones) to carry out a range of surveys and inspections of flooded and other hard to reach areas. The advantages of using drones over regular survey equipment is that they are extremely useful in being able to identify things such as ‘urban creep’ where hard landscaping has prevented water soaking away leading to flooding, or identifying ditches and embankments which are not observable from ground level.
There is also a wealth of hydrology and rainfall data that is readily accessible which I am able to draw on. For example, each month the “Centre for Ecology and Hydrology” (CEH) in conjunction with the “British Geological Survey” (BGS) publish a 12 page Hydrological Summary which details what has happened in the preceding month in respect of rainfall, river flows, groundwater levels, reservoir levels and water resources generally and compares them to long term averages. I am also able to access storm analysis reports from the Met Office which can provide valuable insight into specific flooding events.
In some cases where the cause of flooding is not immediately obvious from initial investigations, hydraulic models can be used to test certain hypotheses.
Hydraulic Models look 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 explore a variety of ‘what if’ scenarios. 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 in depth knowledge of the industry and hydraulic modelling techniques, I am able to provide the legal team with objective scientific information that can clearly determine what has occurred and who is responsible.