Methods to determine sand dune migration benefiting engineering and hydrocarbon companies
Submitting Institutions
University College London,
Birkbeck CollegeUnit of Assessment
Earth Systems and Environmental SciencesSummary Impact Type
EnvironmentalResearch Subject Area(s)
Earth Sciences: Geology, Physical Geography and Environmental Geoscience
Engineering: Geomatic Engineering
Summary of the impact
Research conducted within Birkbeck's Department of Earth and Planetary
Sciences led to the
development of remote sensing and geophysical/geochronological methods to
determine the
movements of sand dunes. These techniques are now used by engineering and
petroleum
companies to plan pipeline routes and infrastructure in deserts, where
migrating sand dunes are a
problem because they can bury or damage infrastructure. For example, ARUP
Consulting have
already used the new methods to inform recommended alignments of pipelines
in two multi-million
pound engineering projects, and have changed their business practice to
include the techniques in
their tender documents for infrastructure projects in desert regions.
Underpinning research
The use of ground-penetrating radar (GPR) to study sand dune stratigraphy
was pioneered by
Birkbeck's Charlie Bristow (Lecturer 1989-2008; Reader 2008-12; Professor
of Sedimentology
2012-present) [1]. This geophysical technique is effective at imaging the
large-scale sedimentary
structures in sand dunes, and can also be used to identify buried objects
within a dune and to
locate the base of a dune so that its thickness can be estimated.
Bristow's first GPR study of sand dune stratigraphy, conducted in 1996,
imaged sedimentary
structures within dunes in Abu Dhabi, and included a comparison of the
radar images with
trenched sections to provide ground truth and to check the accuracy of the
radar interpretation [1].
This work was followed by an investigation of the structure of linear
dunes in Namibia, which found
clear evidence that this type of dune can migrate laterally [2]. Further
investigation of the migration
of sand dunes was then conducted using a novel combination of GPR with
optically stimulated
luminescence (OSL), a technique that enables dune sands to be dated. GPR
profiles were used to
deduce a relative chronology of the sands within a dune, and then this
data was used to design an
efficient strategy for dune dating using OSL [3], enabling the longer-term
rates of dune migration to
be determined. This new methodology was then used to document long-term
(greater than 1,000
years) dune aggradation and to test models of dune stratigraphy [4]. This
work was conducted in
collaboration with Geoff Duller at the University of Wales, who conducted
the OSL dating, and Nick
Lancaster at the Desert Research Institute in the US, who participated in
the fieldwork.
Whilst the migration of sand dunes over long timescales can be
effectively quantified using
Bristow's GPR technique, their short-term dynamics have traditionally been
monitored through
detailed field surveys or long-term surveillance of stakes planted in dune
fields. Recognising that
short-term surveys are labour and time intensive, Birkbeck's Pieter
Vermeesch (RCUK Academic
Fellow 2007-2011; Senior Lecturer 2012) developed a new and more
convenient approach to
monitor the speed and sand flux of migrating dunes, building on the
hand-based methods
employed by King's College's Nick Drake, who introduced the then-current
methodology to
Vermeesch [5]. The approach uses a change detection algorithm, known as
COSI-Corr (Co-registration
of Optically Sensed Images and Correlation), that extracts displacement
fields from
pairs of optical satellite imagery. COSI-Corr was developed in 2007 by
Caltech geophysicists
Sebastien Leprince and Francois Ayoub, and has been applied in various
fields of geomorphology,
the most important of which are studies of earthquakes, glaciers and
slow-moving landslides.
By applying the COSI-Corr change detection algorithm to pairs of
high-resolution optical satellite
images taken at different times, Vermeesch was able to monitor the
migration of dunes in the
Bodélé Depression of northern Chad over time intervals of one month to 6.5
years [5]. The
displacement maps generated from each pair of satellite images were then
used to automatically
distinguish dunes from interdunes. By interpolating a surface between the
interdune areas and
subtracting it from the surface observed by the satellite images, dune
heights and volumes were
then obtained over fine spatial and temporal scales. From this,
pixel-by-pixel estimates of sand flux
were generated, confirming that the Bodélé contains some of the world's
fastest moving dunes [5].
Dune migration rates are a sensitive proxy for the `effective windiness'
of desert areas because
sand flux scales with the cube of wind speed. To take advantage of this
proxy, Vermeesch
extended the COSI-Corr algorithm to compare several satellite images
sequentially. In
collaboration with Caltech's Sebastien Leprince, who provided access to
COSI-Corr's source code,
the new technique was then applied to a 26-year long sequence of archival
satellite imagery from
the Bodélé Depression [6]. The results showed for the first time that dune
velocity, and therefore
wind speed, have remained remarkably constant in this region since 1984.
References to the research
[1] Internal structure of aeolian dunes in Abu Dhabi determined using
ground penetrating radar, C.
S. Bristow, J. Pugh and T. Goodall, Sedimentology, 43, 995-1003
(1996) doi:10.1111/j.1365-3091.1996.tb01515.x
[2] The sedimentary structure of linear sand dunes, C. S. Bristow, S. D.
Bailey and N. Lancaster,
Nature, 406, 56-59 (2000) doi:10.1038/35017536
[3] Combining ground penetrating radar surveys and optical dating to
determine dune migration in
Namibia, C. S. Bristow, N. Lancaster and G. A. T. Duller, Journal of
the Geological Society, 162,
315-322 (2005) doi:10.1144/0016-764903-120
[4] Age and dynamics of linear dunes in the Namib desert, C. S. Bristow,
G. A. T. Duller and N.
Lancaster, Geology, 35, 555-558 (2007) doi:10.1130/G23369A.1
[5] Remotely sensed dune celerity and sand flux measurements of the
world's fastest barchans
(Bodélé, Chad), P. Vermeesch and N. Drake, Geophysical Research
Letters, 35, L24404 (2008)
doi:10.1029/2008GL035921
[6] A 45-year time series of dune mobility indicating constant windiness
over the central Sahara, P.
Vermeesch and S. Leprince, Geophysical Research Letters, 39,
L14401 (2012)
doi:10.1029/2012GL052592
References [2], [4] and [5] best indicate the quality of the
underpinning research.
Relevant research grants:
(i) NERC small grant to Bristow GR9/04055 (£13,250), The structure of
linear dunes: A GPR
survey in the Namib sand sea (1999-2000)
(ii) American Chemical Society Petroleum Research Fund, GLRW2 grant to
Bristow and Lancaster
(US $160,000), Internal Sedimentary Structure of Linear Sand Dunes
(2001-2004).
Details of the impact
The migration of sand dunes can be a huge problem for the construction of
pipelines through
desert terrain. This is because a dune could migrate on to a pipeline and
bury it, or migrate away
from a pipeline and leave it suspended (`free-spanning'), which could
result in a fracture and a
damaging leak of oil or gas. Wind-blown sand is also a hazard to pipelines
as it causes abrasion
and blocks filters. In addition, safety regulations in the countries
concerned often demand that
pipelines be buried to a specific depth (e.g. 2m in Algeria), which is
difficult to achieve in a mobile
dune field.
The method developed by Birkbeck's Vermeesch allows hydrocarbon companies
to use COSI-Corr
to identify desert areas with the greatest sand flux (where dunes are most
active) and areas with
low sand flux (where dunes are least active). They can then use this
information to plan the
location of pipelines and other desert infrastructure to militate against
damage from wind-blown
sand.
The determination of the thickness of active dunes using GPR, as first
demonstrated in Birkbeck
research, is also useful to the hydrocarbon industry. It helps to
constrain pipeline construction cost
estimates, which depend on the volume of sand that has to be moved during
construction, and also
helps determine the safe burial depth for a pipeline. Past practice was to
route pipelines around
dune fields, but this is not possible in parts of Arabia and the Sahara
where oil and gas fields are
directly overlain by dune fields. Given typical construction costs of
$1-$5 million per kilometre,
deviating pipelines is inherently expensive, so it is critical to know the
safest, most direct route.
Following publication of the underpinning research and presentations at
conferences, links were
formed in 2009 with a geomorphology consultancy, Ebor Geoscience Ltd.,
which advises the
hydrocarbon industry on the natural hazards posed by migrating sand dunes.
This led to a number
of pilot studies being commissioned by leading hydrocarbon companies to
evaluate the commercial
benefits of the new methodologies.
In 2010, BG commissioned and invested £68,818 in a study (through
Birkbeck's research office) of
sand dunes in the Grand Erg Occidental using the GPR method. The aim of
the study was to
determine the thickness of active sand dunes within a sand sea where dune
migration is identified
as a hazard for oil and gas pipelines and the construction of processing
facilities. Within the Grand
Erg Occidental, GPR was used to determine if dune sands were thick enough
for pipeline
construction, to test models of dune stratigraphy and to determine if
there is a layer of mobile
dunes migrating over older stabilised dunes, as well as to pick sample
points for OSL dating to
determine longer-term rates of sand dune migration. The results provided a
demonstration that the
methodology is suitable for identifying areas that are most prone to
wind-blown erosion and sand
accumulation (i.e. where dunes are most active), as well as for locating
stable areas that are better
suited to construction. Companies also commissioned and invested money in
pilot studies using
the COSI-Corr method in Algeria and Libya in 2010-11: £13,000 by BP,
£5,000 by ARUP
Consulting and £3,500 by Pipeline Routing Ltd.
The Director of Ebor Geoscience, which served as an intermediary between
the companies (BP,
BG, ARUP and Pipeline) and the Birkbeck researchers who conducted the
pilot studies, reports
that these studies "confirmed that GPR and COSI-Corr represent a
cost-effective way to quantify
the mobility of sand dunes over annual to millennial time scales,
providing key constraints on the
assessment of geo-hazards in arid areas." [A]
Although recent political instability in North Africa has set back many
new infrastructure projects,
with some companies withdrawing from the area, companies have recognised
from the pilot
studies that these new methods provide an advantage over competitors, and
have therefore
adopted the technology. ARUP has used the new techniques on two separate,
very large multi-million
pound pipeline engineering projects in the Algerian desert in 2010 (In
Salah Gas for BP [B]
and Hassi Ba Hamou for BG [B, C]). Both methodologies were used to inform
the recommended
alignment of the route for construction of the pipelines [B]. The work has
also informed decisions
that will result in long-term maintenance cost savings, estimated by ARUP
to be in the order of
several millions of US dollars. The feedback from their clients (BP and
BG) on the results of these
techniques has been very favourable [B]. The Associate Director of ARUP
reported: "Our clients
benefit from application of these techniques through the better informed
decisions and subsequent
cost savings that are made by refining the alignment of major
infrastructure." [B]
Furthermore, as a result of these initial studies and the recognition
that these methods provide an
advantage over competitors, companies have changed their practices to
include assessment of
future damage by wind-blown sand in their tender documents for
infrastructure projects in desert
regions.
For example, Pipeline Routing Ltd. has changed their business model and
will include the COSI-Corr
methodology in future tender documents. In addition, they are developing
an asset
management model based on constant modelling of sand dune migration [D].
The company's
Director said: "COSI-Corr has had a tangible impact on our work because we
can now quantify the
movement of the `terrain', enabling a classification process to feed in to
a Geo-Hazard risk register"
[D]. Pipeline Ltd. produces maps of natural hazards for engineers to use
when picking optimal
routes for new pipelines that minimise the risk at an affordable cost; the
company sees COSI-Corr
as an important tool to quantify the risk posed by migrating sand dunes.
In 2012, ARUP also changed their practice to include assessment of future
damage by wind-blown
sand in their tender documents for infrastructure projects in desert
regions. Their Associate
Director said: "Working with Professor Bristow and Dr Vermeesch, and
application of these new
techniques, has resulted in a step change in our practice for this type of
work." [B] ARUP has
tendered for multi-million pound projects using the new methodologies,
including a railway in the
Emirates (2013) and two projects for which contracts had been won by the
end of July 2013: a BG
pipeline, and a pipeline and gathering station for Petroceltic, all in
Algeria [E].
ARUP has also benefited from the enhanced reputation brought about by the
success of their
COSI-Corr and GPR work. The Associate Director said: "ARUP benefits by
gaining technical
advantage that helps us win future work. We cannot estimate the amount of
commercial work that
has been won directly as a result but we do feel our work with UCL has
enhanced our reputation
and this does protect existing workload and lead to future work with our
clients." [B]
Sources to corroborate the impact
[A] Supporting statement from the Director of Ebor Geoscience Ltd. —
corroborates that the pilot
studies with BP, BG, ARUP and Pipeline confirmed that GPR and COSI-Corr
represent a cost-effective
way to quantify the mobility of sand dunes. Available on request.
[B] Supporting statement from the Associate Director of ARUP Consulting —
corroborates the use
of the techniques to inform recommended pipeline routes and decisions that
will result in long-term
maintenance cost savings. Also corroborates the favourable client
feedback, the change in
practices at ARUP and the impact on ARUP's reputation and workload.
Available on request.
[C] Hassi Ba Hamou Algeria Project, Preliminary Engineering Geological
and Geotechnical
Reconnaissance Interpretative Report (for BG North Sea Holdings Ltd.),
ARUP (2011) —
corroborates ARUP's use of the GRP technique on the Hassi Ba Hamou project
for BG and that
this informed the recommended pipeline route (e.g. see the Executive
Summary, pages i-v).
Available on request.
[D] Supporting statement from the Director of Pipeline Routing Ltd. —
corroborates that the
research has had an impact on the work of Pipeline. Available on request.
[E] The Associate Director of ARUP Consulting can be contacted to
corroborate the use of the new
methodologies in three tenders by ARUP in 2013. Contact details provided
separately.