Sediment transport modelling in Thermaikos Gulf

and 1-way coupling with a high resolution circulation

model Kombiadou Katerina(a), Yannis Krestenitis(a), Margarita Tzali(b),

Sarantis Sofianos(b)

(a) Aristotle University of Thessaloniki, Laboratory of Maritime Engineering(b) University of Athens, Division of Environmental Physics

Aim

High Resolution Circulation

ModelNASMONASMO

3-D Sediment 3-D Sediment Transport ModelTransport Model

Atmospheric Model

SKIRON/EtaSKIRON/Eta

Dust loads

Hydrodynamic - physical

parameters data

Sediment Transport Modelling Platform

Input data:Input data: Particle inflow (rivers, atmosphere etc) Hydrodynamic data (U,V) Physical properties (S,T)

Simulated processes:Simulated processes: Transport-dispersion (random walk method) Flocculation-deflocculation Flock density evolution Effects of stratification to vertical propagation Settling Near-bed processes:

Deposition Consolidation Resuspension Erosion

Model output (potential):Model output (potential): Particle location (x,y,z) Alterations in characteristics (mass, diameter, state) SPM concentrations Sedimentation rates Traces of specific particles Transport patterns investigation

Application in Application in the Thermaikos the Thermaikos GulfGulf

Typical one-year simulation

Simulation dataSimulation data

Simulation period: one year

Source-rivers: Axios – Loudias - Aliakmonas - Pinios

Daily-averaged hydrodynamic-physical parameters input data

6-hour hydrological data

Particle mass: 4320kg

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

13

/41

5/4

17

/41

9/4

21

/42

3/4

25

/42

7/4

29

/41

/53

/55

/57

/59

/511

/51

3/5

15

/51

7/5

19

/52

1/5

23

/52

5/5

27

/52

9/5

31

/52

/64

/66

/68

/61

0/6

12

/6

Mo

f d

us

t e

nte

rin

g t

he

do

ma

in [

t]a

ss

Input data from the UOA atmospheric dust cycle model, based on the SKIRON/Eta modeling system and the Eta/NCEP regional atmospheric model*

* Nickovic, S., Kallos, G., Papadopoulos, A. and Kakaliagou, O., 2001. A model for the prediction of desert dust cycle in the atmosphere. Journal of Geophysical Research, 106: 18113-18129

Available time-series of matter introduced to Thermaikos from the atmosphere from 13/04/05 to 13/06/05 were employed in the simulation

Time-series of aeolian inflowTime-series of aeolian inflow

Application for aeolian-transported matter

Simulation of aeolian-transported matter

TThe he North North AegeanAegean Sea MOdel Sea MOdel (NASMO)(NASMO)

High resolution circulation modelPrinceton Ocean ModelArea:

38.7 – 41.1°Ν

22.5 – 27.1°E

Resolution:

1/60° 1/60° (277x145)

25 vertical sigma-levels

Bathymetry:

U.S. Navy Digital

Bathymetric Data Base I

(1/60° 1/60°)

Atmospheric Forcing:

LAM (SKIRON/Eta):

(0.1° , 1 hour)

Initial & Boundary Conditions :

ALERMO Forecast System

MED-OGCM

ALERMO

NASMO

http://www.bo.ingv.it/mfsDaily 7-day forecast

http://www.oc.phys.uoa.gr/mfstep/bulnaeg/Daily 4-day forecast

http://www.oc.phys.uoa.gr/oceanf.html Daily 5-day forecast

http://www.oc.phys.uoa.gr/mfstep/bulnaeg/Daily 4-day forecast

http://www.oc.phys.uoa.gr/mfstep/bulnaeg/Daily 4-day forecast

SKIRON/Eta SKIRON/Eta atmospheriatmospheric modelc modeldust masses

22.5 22.7 22.9 23.1 23.3 23.5 23.7

39.5

39.7

39.9

40.1

40.3

40.5

40.7

NASMONASMO Hydrodynamic (U,V)

and physical parameters (S,T)

data

2 3 2 4 2 5 2 6 2 7

3 9

3 9 . 5

4 0

4 0 . 5

4 1Thermaikos Sediment Thermaikos Sediment

Transport ModelTransport Model

Area: 39.5-40.8°N & 22.5-23.8°EHorizontal discretization from NASMO [dx=dy=1/60°]Fixed vertical step dz=2m

1-way coupling with circulation model

Preliminary results from a 2day simulation

Simulation dataSimulation data

Simulation period:22/11/07 13:00 – 24/11/07 12:00

Source-rivers:Axios – Aliakmonas - Pinios

Hourly hydrodynamic-physical-hydrological input data

Particle mass: 300kg

Future planning for ECOOP

Development of an operational system able to provide short-term forecasts of sediment loads in the Thermaikos Gulf from atmospheric and/or riverine origin

Utilization of any available data for the validation of the system

Application in the North Aegean?

Sediment Transport Model equations(1)

,, ,i i ii i i i i s i i

dx dy dzu u v v w w w

dt dt dt 3dimensional

displacements

61,1H

i iK

u v rnddt

61,1V

iK

w rnddt

Stochastic displacements

Horizontal diffusion coefficient

Vertical diffusion coefficient

2 221

2Hu v u v

K c dx dyx x y y

2

V Hdz

K Kdx dy

32 22agA ag B ag ag p

dDk C G D k G D D D

dt Particle characteristic diameter

(coagulation-flock break-up)

1ag o we e Particle density

2

18

ag ws ag

w

gw D

Settling velocity

Sediment Transport Model equations(2)

0,91 10

1 0,18 10w

for RpF

Rp for Rp

1 10

Κ exp 0,03 10KvV

for RpF

Rp for Rp

* tU

u F zz

131 100tF Ri

where

5

5 4,

5

0.008 5 10

0.008 0.02 log( ) 4.3 5 10 5 10

0.028 5 10

s

cr dep s s

s

for w m s

u w for w m s

for w m s

,

,

b cr er

cr er

, , , , 1 n tcr res cr dep cr er cr dep e

Deterministic and stochastic displacement damping functions for the parameterization of the stability of the stratification of the water column

Shear stress velocity

Critical shear velocity for particle deposition

Erosion rate

Critical shear stress for particle resuspension (shelf-weight consolidation)

Effect of the stratification of the water column

where: α is the thermal expansion rate β the haline contraction rate

The density ratio Rp, expresses the influence of temperature and salinity to the stability of the water column, and is defined as the ratio of the contribution to the ambient density of the stabilizing parameters to the contribution of the destabilizing parameters.

Rp is defined as:

Double diffusive processes occur for 1 Rp 10 Thus a threshold value of the density ratio, above which the stratification can be considered as stable is Rp10 Density ratios that have been defined from the physical parameters one-year input data present largest values of the ratio in the surface waters in the vicinity of the river estuaries

SzR

Tz

0,91 10

1 0,18 10w

for RpF

Rp for Rp

1 10

Κ exp 0,03 10KvV

for RpF

Rp for Rp

Stochastic vertical velocity damping function

Deterministic vertical velocity damping function

The proposed damping functions (1)

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1 10 19 28 37 46 55 64 Rp

Fw

Deterministic and settling velocity damping function: the experiments of Green (1987) and Parsons and Garcia (2000) were put to use. Figure presents the dimensionless finger settling velocity with relation to the value of the density ratio, whereas the fitted curve represents the damping function of the non-fluctuating components of the vertical velocity Fw.

0,91 10

1 0,18 10w

for RpF

Rp for Rp

The proposed damping functions (2)

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1 10 19 28 37 Rp

F Kv

Stochastic vertical velocity: the simplified parameterization of Zhurbas et al. (1987) for the vertical diffusivity of salt and temperature following exponential decrease of the density ratio has been applied. Figure presents values of the corresponding stochastic velocity damping function FKv along with experimental data by Hoyal et al. (1999) for the double diffusive flux coefficient, manipulated to express the ratio of the flux to the diffusion coefficient of the fastest diffusing substance.

1 10

Κ exp 0,03 10KvV

for RpF

Rp for Rp

Stability ratios defined by hydrodynamic input data

The animation presents the regions in which the density ratio takes values of Rp>10

Thus it depicts the areas the stratification is strong enough to trap sediments

Consolidation

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38

consolidation days

exp(-nt)

0.1

0.11

0.12

0.13

0.14

0.15

0.16

0.17

0.18

0.19

0.2

τ cr,res

e(-nt)τcr,res

min minn t

oe e e e e

, , , , 1 n tcr res cr dep cr er cr dep e

Porosity and critical shear stress threshold for resuspension evolution with consolidation time (for n=1,5·10-5s-1)

Accepting: full consolidation in 38 days

critical shear stress for deposition 0.1Pa

critical shear stress for erosion 0.2Pa

*http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=16887

Application for aeolian-transported matter

Powerful winds pulled a thick band of desert dust from Egypt and Libya over the Mediterranean Sea on April 17, 2005. The dust is so thick that Crete is completely obscured from view, and the ground of Greece is barely visible. African dust frequently blows over the Mediterranean in the spring, carrying tons of dust into Greece. The winds that produced this dust storm blew at an average of 75-89 kilometers per hour (47-55 mph) near the sea’s surface, and stronger winds prevailed higher in the atmosphere. The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite captured this photo-like image of the storm.*

The image is a property of NASA

ReferencesBurd, A., Jackson, G. A.: Prediction particle coagulation and sedimentation rates for a pulsed input, Journal of Geophysical Research, 102 C5, 10545-10610, 1997Green, Th.: The importance of double diffusion to the settling of suspended material, Sedimentology, 34, 319-331, 1987Hoyal, D.C.J.D., Bursik, M.I. and Atkinson, J.F.: Settling driven convection, a mechanism of sedimentation from stratified fluids, Journal of Geophysical Research, 104 (C4), 7953-7966, in press, 1999 Huthnance, J. M. et al.: PROFILE – Processes in Regions of freshwater Influence, Final Report, POL Internal Document No 102 – Thermaikos Bay, 1997Mellor, G. L.: Introduction to Physical Oceanography, Princeton University, New Jersey, 1996Metha, A.J.: Hydraulic Behaviour of fine sediment, Coastal, Estuarial and harbour engineer's reference book, Abott & Price, Chapman & Hall (Pubs.), London, 577-585, 1993O’ Brien, J.J. (ed.): Advanced Physical Oceanographic Numerical Modelling, NATO ASI Series, 1985-86Parsons, J.D. and Garcia, M.H.: Enhanced sediment scavenging due to double-diffusive convection, Journal of Sedimentary Research, 70(1), 47-52, 2000Toorman, E.A., Bruens, A.W., Kranenburg, C. and Winterwerp, J.C.: Interaction of Suspended Cohesive Sediment and Turbulence, Proc. INTERCOH, 2000Winterwerp, J. C.: On the dynamics of high-concentrated mud suspensions, Judels Brinkman & Ammerlaan, Delft, 1999Zhurbas, V. M., Kuzmina, N. P., and Kulsha, Y.: Step-like stratification of the ocean thermocline from transformations associated with thermohaline salt finger intrusions (numerical experiment), Oceanology, 27, 277–281 English translation, 1987