It has been the wettest winter on record and
one when the expertise of British Geological Survey staff was in high demand as
flooding extended across much of southern England. At the same time we feel
very sorry for those who have been and continue to be materially affected by
the flooding and the impacts of the extremely wet ground.
The British Isles are located on the edge of
the European tectonic plate system and this location has underpinned a number
of our geographic and geological attributes. The one in play over the past few
months is that we face the Atlantic Ocean and in particular, we are subject to
the position of major geographical fluxes such as the atmospheric Jet Stream
and also the Atlantic Gulf Stream. The long
term research that is ongoing and needed is to be able to better predict the
weather patterns and in a given year, to allow people and government, to
prepare for them. I note that at almost exactly the same period two years ago,
BGS staff were advising government on the risks of a severe drought as we had
not received enough rain over the two previous winters.
Some might feel that the British climate is
just too difficult to forecast. I think we are making strides and there are
indications that we know what triggers the trajectory of the Jet stream and
observations on the Gulf Stream show some significant changes in warm water
ocean flux that must link to our weather patterns (NERC Rapid Watch). How these fluxes are
being affected by climate change is also an important line of research, as we
know that the Earth is absorbing more heat, but we do not yet know how this
links to climate change. We do know, for example, that the fluctuations
associated with the El Niño/Southern Oscillation (ENSO) have favoured a cool La
Niña phase in the past few years and when this shifts the planet will most
likely accelerate into a warmer climate.
When the rain falls, it either evaporates, is
taken up by vegetation, runs off or soaks into the ground. It is this underground flow that is the
research realm of our BGS groundwater scientists. A large amount
of the flooding in the Thames valley and across southern England is related to groundwater flooding, where the ground is
completely saturated, the underground aquifers are full and the gradients in
topography result in groundwater emerging at the surface in places where it has
never, or very infrequently, appeared before. Some streams in the chalk of
southern England are flowing for the first time in living memory.
Interestingly, even in a normal flow regime ~ 65% of the water in the Thames in
London is sourced from groundwater and not surface water and it is groundwater
that keeps many of our rivers flowing during the summer months.
What can we do to help the people who are
struggling and inform the government? We can provide estimates of how long
flooding will continue, based on the predicted rainfall patterns and or
knowledge of how our aquifers respond, and we can model where groundwater
flooding will be the most serious, although that is of little help to those
who's homes are already flooded. We can also help provide information on
protecting important infrastructure and future planning. Because groundwater
flooding has only relatively recently been recognised as a serious issue, there
is only limited information on historical events and so it is as just as
important that we invest in the research needed to improve our understanding of
groundwater flooding and develop resilience as it is to be able to predict the
weather.
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| Oxford Floods 2014 BGS (c) NERC |
High rainfall amounts and ground saturation and
shallow groundwater flow also result in increased landslides and sinkhole risk. These commonly form in areas where
clays or sand-rich sediments overly soluble rocks such as the Chalk or Gypsum.
BGS has maps of areas most likely to be susceptible to landslides, underground
solution features (sinkholes) or mobility of rocks. These help inform
insurance and construction companies, but prediction of where an event might
happen is extremely difficult especially in urbanised areas. In mountain ranges
and rural areas it is possible to use ground measuring satellites coupled to
systems in the ground to measure movement and indeed some of the
most threatening landslides and subsidence areas on the planet are monitored
constantly.
BGS staff have worked hard in providing
information to the public and government and also worked with the press in
helping explain to the public how exceptional this particular flooding crisis
is. We must however continue to better prepare for the next crisis
whether is from too much or too little rainfall input into our catchments.
