The dynamics of turbidity zones intidal estuaries

Hans Burchard

�

and Manuel Ruiz Villarreal

�

hans.burchard@io-warnemuende.de.

1. Baltic Sea Research Institute Warnemunde, Germany2. Institute for Oceanography, University of Hamburg,

Germany

GHAMES-Seminar in Liege, June 13, 2002 – p.1/19

Program of the talk

� Phenomenology

� Conceptual models

� Numerical simulations (historical)

� Numerical simulations (recent)

� Conclusions

GHAMES-Seminar in Liege, June 13, 2002 – p.2/19

Map of the tidal Elbe

9°00' 10' 20' 30' 40' 50' 50' 40' 30' 10°00'

54°00'

53°30' 0 10km

53°40'

53°50'

20' 8°10'

54°10'

Scharhörn

Gr. Knechtsand

Neuwerk

Cuxhaven

Friedrichskoog

Oste

Nord-

Ost

see-

Kana

l

Stör

Wischh. Süderelbe

Schwinge

Krückau

Pinnau

Este

Lühe

Med

em

Brunsbüttel

Glückstadt

Stade

Hamburg 630

640 650

660

670

680

690

700

710 720

730

740

Strom-km 700

Trischen

Watt

WGE Be 10.96

Mühlen- berger Loch

Pagensand

Medemgrund

Neufelder Sand

Großer Vogelsand

Medemsand

Gelbsand

GHAMES-Seminar in Liege, June 13, 2002 – p.3/19

PhenomenologySPM observations in the tidal Elbe

Pers. comm. Jens Kappenberg

GHAMES-Seminar in Liege, June 13, 2002 – p.4/19

PhenomenologySPM observations in the tidal Elbe

Pers. comm. Jens Kappenberg

GHAMES-Seminar in Liege, June 13, 2002 – p.5/19

PhenomenologySPM observations in Columbia River

Salinity

SPM

Pers. comm. David Jay, Phillip Orton

GHAMES-Seminar in Liege, June 13, 2002 – p.6/19

Classical conceptual models

� Flocculation of riverine colloids due to the ioncontent of the saline sea water (Lucht [1953]).

� "The peculiar process of mixing between riverineand marine water in the tidal zone works as aSPM trap." (Postma und Kalle [1955]).

Schoellhamer & Burau, 1998

GHAMES-Seminar in Liege, June 13, 2002 – p.7/19

Classical conceptual modelsDensity currents from numerical lock exchange

� � �

h

-15

-10

-5

10 20 30 40 50 600

1

2

3

4

5

x / km

z / m

PSfrag replacements

��� / kg m � �

GHAMES-Seminar in Liege, June 13, 2002 – p.8/19

Conceptual model

Jay & Musiak, 1994

GHAMES-Seminar in Liege, June 13, 2002 – p.9/19

Computer simulations

Burchard & Baumert, 1998

GHAMES-Seminar in Liege, June 13, 2002 – p.10/19

Computer simulations

Burchard & Baumert, 1998

GHAMES-Seminar in Liege, June 13, 2002 – p.11/19

Computer simulations

Burchard & Baumert, 1998

GHAMES-Seminar in Liege, June 13, 2002 – p.12/19

GETM

� Three dimensional, hydrostatic, free surface, baroclinic

� Mode-splitting, Arakawa-C grid

� Horizontal coord.: Cartesian, spherical or orthogonal

� Vertical coord.: Sigma, z-levels or generalized

� Turbulence closures from GOTM (http://www.gotm.net)

� Various advection schemes for momentum and tracers

� Stable drying and flooding algorithm

Burchard & Bolding, 2002

GHAMES-Seminar in Liege, June 13, 2002 – p.13/19

Suspended matter moduleTransport equation:

��

� � ��� ��� � � � �� �� � � � ��� � ��� � � � � � �� ��� ��

��� � � � �

(1)

Bottom boundary condition:

� � � � ��

�� � � ��� � � (2)

Erosion & sedimentation flux:

��� � � ����

���� �� � � � � �! � � � � � � �� � �

���� �� � � � �#" (3)

Bottom SPM pool: ��

�$ � � � � �%� (4)

GHAMES-Seminar in Liege, June 13, 2002 – p.14/19

Two-dimensional experiments

� Salinity and SPM (click for animation), noadvection of turbulence

�

Salinity and eddy diffusivity (click for animation),no advection of turbulence

�

Salinity and eddy diffusivity (click for animation),with advection of turbulence

GHAMES-Seminar in Liege, June 13, 2002 – p.15/19

Idealised bathymetry

GHAMES-Seminar in Liege, June 13, 2002 – p.16/19

Three-dimensional experiment

� Salinity and SPM, longitudinal section (click foranimation)

� Salinity, SPM and velocity, surface view (clickfor animation)

� Salinity and velocity, cross-sectional view (clickfor animation)

GHAMES-Seminar in Liege, June 13, 2002 – p.17/19

Conclusions

� In many estuaries, turbidity maxima (ETMs) areobserved at the tip of the salt intrusion.

� These types of ETMs have been numericallysimulated with different 2D- and 3D-models.

� Two major ETM generation mechanisms havebeen pinpointed, residual gravitational circulationand tidal velocity asymmetry.

� Even in idealised 3D cases, complex secondaryflows occur and strongly influence the ETMdynamics.

GHAMES-Seminar in Liege, June 13, 2002 – p.18/19

Future work

� Detailed numerical analysis of ETM dynamics inthree dimensions.

� Numerical analysis of turbulence advection.

� Application of the model to process studies in thetidal Elbe by using a curvi-linear orthogonal grid.

GHAMES-Seminar in Liege, June 13, 2002 – p.19/19