Ph.D. Studentship
Sediment-laden density currents
Supervised by Peter A. Allison, Matthew D. Piggott &
The presence of suspended sediment in an aquatic flow increases the density of the flow.
When such a flow enters a still water body it behaves as a density current and travels down
slope and progressively mixes with the ambient water and rains out suspended sediment.
These flows occur at a range of scales and examples include: effluent outflows, riverine
discharge into lakes and marine sediment laden currents that can run for 1000s of km. The
latter have substantial erosive power and pose a significant geohazard to submarine pipelines
and cables, and have in the past triggered fatal tsunamis. At the global scale they are also
responsible for transporting significant quantities of sand and mud into the deep ocean. The
sediments laid down by such flows, turbidites are characterized by waning flow and typically
have a lower part that is composed of clean sands. Such sands are well known as potential
hydrocarbon reservoirs and are active exploration targets.
Knowledge of the generation and propagation of these flows is clearly important but there is a
limit to the value of experimental simulations and numerical simulations have clear appeal.
However, such simulations are numerically challenging, the flows themselves are typically
turbulent and modeling the dynamics and mixing of the flow is computationally expensive.
Figure 1: A) Unstructured mesh of the Earth.
Note increased resolution in areas of
bathymetric change and complexity. B) Tidal
(lunar semi-diurnal) model of the Earth in Aptian
(Cretaceous) times using an unstructured mesh.
C) Gravity current flowing down an idealised
slope. This uses an adaptive mesh which
dynamically focuses resolution on those areas
of the simulation that require it. Note also that
this model is non-hydrostatic and thus captures
the mixing associated with the Kelvin-Helmholtz
billows at the density interface. An adaptive,
non-hydrostatic model will be crucial to model
the flow of sediment-laden density currents
down modern and ancient slopes.
The Applied Modelling and Computing Group (AMCG) at Imperial College has developed a
state-of-the-art finite element model (Fluidity-ICOM) that utilizes an adaptive mesh that
dynamically focuses computational resource on areas of evolving flow complexity (Fig. 1).
This facilitates considerable computational efficiency. The model has been used to model a
variety of flows and oceanic phenomena (Piggott et al, 2008; Mitchell et al, 2010a,b; Wells et
al, 2010) and recent developments include the capacity to model the deposition and
entrainment of sediment from dilute flows.
As a first step the student will validate recent code developments against published and
bespoke experimental data and have the opportunity of collaborating on laboratory flume
experiments generating validation data. S/he will:

Define the limitations and operation of this new model and produce an operations
manual for future users.

Develop the model to predict areas where specific sediment bedforms may develop.

Evaluate the impact of bathymetry (slope angle, bed smoothness, flow obstacles) on
flow propagation on sedimentation.
Ph.D. Studentship
The student will join a well-funded and vibrant multi-disciplinary group
(http://amcg.ese.ic.ac.uk/index.php?title=Main_Page) of around 50 scientists, engineers and
computational numericists in the Department of Earth Science and Engineering at Imperial
College London. The group provides both formal and informal training in model development
and application and works closely with geologists involved in petroleum exploration.
This project will suit a numerate graduate with a First Class degree in either physics,
geophysics, maths or an engineering subject.
References
Mitchell, A.J., Allison, P.A., Piggott, M.D., Gorman, G.J., Pain, C.C., Hampson, G.J., Numerical modelling of tsunami
propagation with implications for sedimentation in ancient epicontinental seas: the Lower Jurassic Laurasian Seaway,
Journal of Sedimentary Geology (2010a), Vol:228, Pages:81-97.
Mitchell, A.J., Ulicny, D., Hampson, G.J, Allison, P.A., Gorman, G.J., Piggott, M.D., Wells, M.R., Pain, C.C., Modelling tidal
current-induced bed shear stress and palaeocirculation in an epicontinental seaway: the Bohemian Cretaceous Basin,
Central Europe, Sedimentology, (2010b), Vol: 57, Pages:359-388.
Piggott M.D, Gorman G.J, Pain C.C., Allison P.A., Candy A.S., Martin B.T., Wells, M.R., A new computational framework
for multi-scale ocean modelling based on adapting unstructured meshes, International Journal for Numerical Methods
in Fluids, (2008), Vol:56, Pages:1003-1015.
Wells, M.R., Allison, P.A., Piggott, M.D., Hampson, G.J., Pain, C.C., Gorman G.J., Tidal modeling of an ancient tide-dominated
seaway, part 2: the Aptian Lower Greensand seaway of norwest Europe, Journal of Sedimentary Research, (2010a),
Vol:80, Pages:411-439.
Wells, M.R., Allison, P.A., Piggott, M.D., Hampson, G.J., Pain, C.C., Gorman G.J., Tidal modeling of an ancient tide-dominated
seaway, part 1: model validation and application to global early Cretaceous (Aptian) tides, Journal of Sedimentary
Research, (2010b), Vol:80, Pages: 393-410.