Post on 07-Aug-2020
Galveston (TX, USA), 10/18/2018
Impact of small bathymetric
changes on large-scale
hydrodynamics Robert Hagen, Janina Freund and Frank Kösters
PECS 2018
19F2004A
www.baw.de | www.mdi-de.baw.de/easygsh/
Modeling area
Page 2
Imag
ery
rep
rod
uced
fro
m t
he G
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_2014 G
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20150318, w
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Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
10/18/2018
Introduction Results Analysis Summary
www.baw.de | www.mdi-de.baw.de/easygsh/
Objective
Page 3 10/18/2018
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
Reference 2006
Forcing-induced differences Scenario:
Scenario:
Introduction Results Analysis Summary
Scenario: Bathymetry 2006
Forcing 2010
Scenario: Bathymetry 2010
Forcing 2006
Research with coarse, large-area coastal models implies, that changes in bathymetry result in large scale differences in
tidal dynamics (e.g. Jacob et. al., 2015)
These changes have neither been confirmed with long simulation periods, high-resolution approaches nor have they
excluded meteorological influence. Also, calibrated estuaries and high-resolution wetting and drying have been
neglected
Bathymetry-induced differences
www.baw.de | www.mdi-de.baw.de/easygsh/
Grid resolution in focus area (German Bight: 30m to 2,000m)
3D approach with focus area
Estuaries included until tidal weir
Increased accuracy with subgrid technology
Goal: 20 year hindcast (1996-2015) available for download
Model Setup
Page 4
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
10/18/2018
Introduction Results Analysis Summary
725 km
450 miles
German
Bight
Model-area:
full domain
Model-area:
Partial focus area
Elbe estuary
www.baw.de | www.mdi-de.baw.de/easygsh/
The principle behind subgrid models
Page 5
A cell is divided m times
Subedges receive depths
The cell has a depth distribution
-25
-20
-15
-10
-5
0
5
10
AREA
VOLUME
10/18/2018
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
Ba
ckg
rou
nd
s b
y B
KG
To
pP
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.bu
nd
.de
; G
rid
© E
asyG
SH
-DB
Introduction Results Analysis Summary
www.baw.de | www.mdi-de.baw.de/easygsh/
Advanced wetting and drying with subgrid
Page 6
Cells can be partially wet
Exact representation of water volume
Better representation of tidal flats
Integration of groins and training walls
These are hydraulically efficient
10/18/2018
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
Training wall
Dry area
Partially wet
Completely wet
© b
y E
asyG
SH
-DB
Introduction Results Analysis Summary
www.baw.de | www.mdi-de.baw.de/easygsh/
Bathymetry changes in the mouth of the Elbe estuary: 2010 - 2006
Page 7
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
10/18/2018
deeper shallower
Introduction Results Analysis Summary
www.baw.de | www.mdi-de.baw.de/easygsh/
Forcing
Bathymetry
Wate
r le
vel
[m]
Tid
e R
an
ge
[Th
b]
Tide Mean Water [Tmw]
Ebb Flood
- Tide High Water: Highest water level in tide cycle
- Tide Low Water: Lowest water level in tide cycle
- One tide cycle contains 1x Thw and 2x Tnw
- Tide Range: Difference between Thw and Tnw(1,2)
Tide High Water [Thw]
Tide Low Water [Tnw]
Comparing the forcing of 2006 and 2010
Page 8
Impact of small scale bathymetry changes on large scale hydrodynamics | Robert Hagen; Janina Freund; Frank Kösters
10/18/2018
Time [h]
Introduction Results Analysis Summary
www.baw.de | www.mdi-de.baw.de/easygsh/
Influence of nodal tide
Page 9
Large area variations in deep water result from nodal tide.
Nodal Tide varies around 3cm between 2010 and 2006
Meteorology suggests 2006 to be windier, therefore the tidal range
is larger in 2010 even though astronomy decreases tidal component
amplitudes at the same time.
Nodal tide ( 3cm)
10/18/2018
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
Increase
Decrease
Introduction Results Analysis Summary
www.baw.de | www.mdi-de.baw.de/easygsh/
Differences (Tidal range), scenario - reference
Page 10 10/18/2018
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
Δforcing-induced differences Δbathymetry-induced differences
Introduction Results Analysis Summary
de
cre
ase
inc
rease
Tidal range has
increased from
1 to 8 cm.
Changes affect
large-scale
hydrodynamics.
Tidal range has
increased and
decreased.
Changes affect
local
hydrodynamics.
www.baw.de | www.mdi-de.baw.de/easygsh/
Differences (Flood current velocity magnitude ), scenario - reference
Page 11 10/18/2018
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
Δforcing-induced differences Δbathymetry-induced differences
Introduction Results Analysis Summary
de
cre
ase
inc
rease
Flood current
velocity is not
affected.
Changes affect
local
hydrodynamics.
Flood velocity
has increased
and decreased.
www.baw.de | www.mdi-de.baw.de/easygsh/
Correlation between
- bathymetry
- tidal range
Correlating bathymetry differences with hydrodynamics
Page 12
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
10/18/2018
hig
her
lo
wer
shallower deeper
(Δvalue | Δdepth)
Introduction Results Analysis Summary
de
cre
ase
incre
ase
www.baw.de | www.mdi-de.baw.de/easygsh/
Correlating bathymetry differences with hydrodynamics
Page 13
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
10/18/2018
Introduction Results Analysis Summary
R = -0.10
de
cre
ase
incre
ase
www.baw.de | www.mdi-de.baw.de/easygsh/
Correlating bathymetry differences with hydrodynamics
Page 14
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
10/18/2018
Introduction Results Analysis Summary
de
cre
ase
incre
ase
R = -0.21
www.baw.de | www.mdi-de.baw.de/easygsh/
Correlating bathymetry differences with hydrodynamics
Page 15
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
10/18/2018
Introduction Results Analysis Summary
R = -0.29
de
cre
ase
incre
ase
www.baw.de | www.mdi-de.baw.de/easygsh/
Color-coding differences of bathymetry and hydrodynamics
Page 16
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
10/18/2018
Introduction Results Analysis Summary
de
cre
ase
incre
ase
www.baw.de | www.mdi-de.baw.de/easygsh/
Changes of tidal range due to deepening of bathymetry in the Elbe estuary
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Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
10/18/2018
deep
er
sh
all
ow
er
decrease
increase
Introduction Results Analysis Summary
www.baw.de | www.mdi-de.baw.de/easygsh/
Mean tidal range due to shallower bathymetry in the Elbe estuary
Page 18
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
10/18/2018
Introduction Results Analysis Summary
deep
er
sh
all
ow
er
decrease
increase
www.baw.de | www.mdi-de.baw.de/easygsh/
Mean tide velocity due to deepening of bathymetry in the Elbe estuary
Page 19
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
10/18/2018
Introduction Results Analysis Summary
deep
er
sh
all
ow
er
decrease
increase
www.baw.de | www.mdi-de.baw.de/easygsh/
Mean tidal velocity due to shallower bathymetry in the Elbe estuary
Page 20
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
10/18/2018
Introduction Results Analysis Summary
deep
er
sh
all
ow
er
decrease
increase
www.baw.de | www.mdi-de.baw.de/easygsh/
2010 2006
Bathymetry in the mouth of the Elbe estuary: 2006 and 2010
Page 21 10/18/2018
Background © by BKG TopPlusOpen www.bkg.bund.de
Introduction Results Analysis Summary
Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
www.baw.de | www.mdi-de.baw.de/easygsh/
A North-Sea model with high-resolution in shallow water has been built to reproduce hydrodynamics from 1996 to 2015
A well calibrated reference run (2006) has been varied with the forcing (scenario 1) and bathymetry (scenario 2) of 2010
Results:
The forcing produced large-scale differences in tidal dynamics (by meteorology)
Small-scale bathymetry variation produces local changes in hydrodynamics
Direct correlation of local hydrodynamics with bathymetry variation is rather weak
Outlook and future tasks
Extend the temporal space to analyze larger bathymetry differences, because large-scale implications were not found
Summary and Outlook
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Impact of small bathymetric changes on large-scale hydrodynamics| Robert Hagen; Janina Freund; Frank Kösters
1996 2006 2010 2015
Introduction Results Analysis Summary
www.baw.de | www.mdi-de.baw.de/easygsh/
References
Web references
EasyGSH-DB: http://mdi-de.baw.de/easygsh/ ; (bathymetry, sediment and hydrodynamic data available for download)
WMS: TopWebPlus (grey); www.bkg.de ; (available for everyone)
WMS: Imagery reproduced from the GEBCO_2014 Grid, version 20150318, www.gebco.net ; (available for everyone)
Other references
JACOB, B.; STANEV, E. V. and ZHANG, Y. J.: Local and remote response of the North Sea dynamics to morphodynamic
changes in the Wadden Sea. In: Ocean Dynamics, Vol. 66, 5, 671-690, doi: 10.1007/s10236-016-0949-8, 2016.
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