CBL - Campus del Baix Llobregat

Projecte llegit

Títol: Modelling the exchange of small plastics between the inner surf zone and the open sea under different beach configurations


Estudiants que han llegit aquest projecte:


Director/a: RIBAS PRATS, FRANCESCA

Departament: FIS

Títol: Modelling the exchange of small plastics between the inner surf zone and the open sea under different beach configurations

Data inici oferta: 01-11-2019     Data finalització oferta: 31-05-2020



Estudis d'assignació del projecte:
    GR ENG SIST AEROESP
Tipus: Individual
 
Lloc de realització: EETAC
 
Nom del segon director/a (UPC): Albert Falqués Serra
Departament 2n director/a:
 
Paraules clau:
Fluid mechanics, Numerical methods, Marine plastic debris
 
Descripció del contingut i pla d'activitats:
The leakage of plastic debris
into the ocean is a major
environmental problem because
the amount of plastic in the
marine ecosystems is
exponentially growing and it
could become dangerous for
animals and people (Koelmans et
al., 2017). However, the present
understanding of the marine
plastic budget and of plastic
motion through the ocean is
inadequate, prompting the EU to
make this issue a top science
priority and funding research
projects like TOPIOS
(http://topios.org/). About 60%
of the plastic emitted to the
ocean initially floats (it has a
density lower than sea water).
Also, plastic size is variable
and it is classified as
macroplastic (d > 5 mm),
microplastic (5 mm > d > 0.335
mm) and nanoplastic (d < 0.335
mm) (Koelmans et al., 2017).

One of the present open problems
is the exchange of plastic
between land and ocean through
sandy coasts, which are about
25% of the coasts on a global
scale. The swash and surf zones
of sandy beaches, where breaking
waves, currents and sediment
interact in a complex nonlinear
way, are highly variable and its
internal dynamics can strongly
affect the motion of plastics
(Castelle and Coco, 2013). This
internal dynamics include the
common formation of alongshore-
rhythmic sandy patterns like
mega-cusps, transverse bars and
crescentic bars (Garnier, 2006),
which are coupled to the
presence of seaward directed
rip-currents that can enhance
the flushing of floating
material towards the ocean
(Castelle and Coco, 2013).

The focus of this study is to
quantify how the morphological
beach configuration affects the
exchange of small plastics
between the swash zone and the
open sea. For this, an existing
nonlinear model called morfo55,
which describes the dynamics of
waves, currents, sediment and
sea bed level (Garnier, 2006),
will be run to create several
study cases with different beach
conditions. Using the wave and
water velocity fields obtained
with morfo55, an
advection/diffusion equation for
the concentration of plastics
will be applied to quantify its
evolution.

Planned activities:

Task 1: Get acquainted with: i)
the problem of marine plastic
debris, ii) the fundamentals of
beach morphodynamics and morfo55
model, iii) numerical methods
based on finite differences.
About 2 weeks.
Task 2: Construct a Matlab code
that solves numerically the
advection/diffusion equation for
the plastic concentration and
test it against an analytical
case. About 2 weeks.
Task 3: Use the Morfo 55 code to
generate the steady wave and
water velocity fields for
different study cases: e.g.,
with a shore-parallel bar (and
different wave height, period
and angle) and with a crescentic
bar (and different wave height,
period and angle). About 4
weeks.
Task 4: Read the steady wave and
velocity field of morfo55 in the
Matlab code and solve the
concentration equation for the
different study cases. Quantify
the exchange of plastic between
the swash zone and the open sea.
About 6 weeks.
Task 5: Introduce the
advection/diffusion equation for
the concentration in Morfo55 and
solve it under unsteady
conditions (for example, under
the occurrence of shear
instabilities of the longshore
current). About 6 weeks.
Task 6: Write the TFG thesis.
About 3 weeks.

References:

Castelle, B., and Coco, G.
(2013). Surf zone flushing on
embayed beaches, Geophys. Res.
Lett., vol. 40, 2206-2210,
doi:10.1002/grl.50485.
Garnier, R. (2006). Nonlinear
modelling of surf zone
morphodynamical instabilities,
PhD thesis, ed. by Universitat
Politecnica de Catalunya,
December 2006.
Koelmans, A.A., Kooi, M.,
Lavender Law, K., and van
Sebille, E. (2017). All is not
lost: deriving a top-down mass
budget of plastic at sea,
Environ. Res. Lett., vol. 12,
114028, doi:
https://doi.org/10.1088/1748-
9326/aa9500
 
Overview (resum en anglès):
This document shows the procedure carried out to model the Exchange of small plastics between the inland surfing area and the open sea under different beach configurations. The damage caused by plastics to the ocean and the fauna it has contained for years is an emerging and increasingly studied problem. To fully understand the dynamics that a plastic can have on the surface of the water you must know the morphodynamics of the beaches, where many events occur simultaneously at different scales that continuously deform the beach, is a complex and difficult to predict place. Using a model called MORFO55 developed by the Group of Nonlinear Fluid Dynamics of the UPC we managed to obtain reliable data from this morphodynamics and with this data and using Matlab software we developed an algorithm capable of showing the dynamics of a plastic under different configurations. The main objective of this project is to observe how the formation of a rhythmic sand pattern along the coast called crescent bar or crescent bar influences and therefore the formation of a system of deep currents influences the dynamics. of these plastics on the surface of the water.


© CBLTIC Campus del Baix Llobregat - UPC