Global Journal of Engineering Sciences (GJES)
Overlooked
impacts of climate change on groundwater
Authored by Helen Rutter
Opinion
Climate change is a current
area of huge concern. City, district and regional councils are grappling with
climate change implications for their respective areas and what advice they
should provide to stakeholders about housing, infrastructure and land use into
the future. There are many specific issues, including impacts of extreme
events, long-term changes in rainfall or weather patterns that might affect the
ability to grow crops, and coastal inundation from sea level rise. However,
there are also some more subtle, but still important, aspects of climate change
that are often overlooked, for example:
• Changing drinking water
source reliability, for example due to increased flood flows in rivers and
increased sediment loading, restricting the ability to take water, or decreased
recharge to aquifers resulting in lower groundwater levels and less available
allocation. In deep groundwater, effects of reduced recharge may not be seen
for many years: and in contrast, the response to increased recharge may be prolonged,
making planning for climate change effects difficult.
• Impacts from shallow
groundwater in urban areas, including increased inundation of infrastructure,
contribution to surface water flooding, and increased liquefaction risk.
Shallow groundwater levels usually respond rapidly to rainfall events, and may
cause surface inundation and/or reduce infiltration capacity in response to
rainfall. Shallow groundwater in coastal areas, in addition, will be impacted
by rising sea levels, further reducing the available “headroom”. Horizontal
infrastructure will be negatively impacted, with the potential for increased
infiltration into waste water pipe systems, and derogation of infrastructure in
areas where groundwater levels are impacted by tidal effects and intrusion of
saline water. Shallow groundwater also impacts on the ability to carry out
excavation work (see Figure 1), and may even have an impact on types of
vegetation to plant.
• Impacts of shallow
groundwater or SLR on land treatment of effluent and land drainage. In many
areas of the world, application of treated effluent to the land is a necessary
part of effluent treatment, but relies on there being sufficient unsaturated
thickness to work. Control of shallow groundwater levels is sometimes facilitated
by land drainage. In coastal areas, again shallow groundwater will respond to
rainfall and sea level rise, and the combination of both increased extreme
events and general SLR-induced groundwater levels may result in systems being
unworkable.
Groundwater is often
out-of-sight, out-of-mind, but consideration of these less obvious impacts of
climate change is essential in order to be fully prepared for the future. In
New Zealand, there are questions being asked including ones around land
development decisions, controlling shallow groundwater infiltration into
services to minimise volumes arriving at treatment centres, life-expectancy of
existing infrastructure, and questions around sustainability of water supply
sources.
However, groundwater
is a 4-dimensional problem: it varies in space, with depth, and with time. It
can’t be dammed, and stop banks can’t keep it out. It is on continuity with
surface water, with flows going either way, depending on relative levels.
Currently, in New
Zealand, central and local government are addressing many of the obvious
climate change impacts. However, attention to the “overlooked impacts” is less
coordinated. Individual councils, sometimes through research projects, but more
often through their own funding, have identified specific issues within their
own areas, and are investigating them at varying levels of detail.
In order to be able to
understand, and predict, how groundwater levels will respond to future climate
change, we need to be designing appropriate monitoring now, aiming to be able
to understand the current scenario, and model future impacts. Unless we are
proactive about this, there will be a huge lost opportunity cost, and we will
be counting this for many years to come.
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