slide1
Download
Skip this Video
Download Presentation
Luc Lebbe , Sarah Jonckheere & Alexander Vandenbohede Department of Geology and Soil Science,

Loading in 2 Seconds...

play fullscreen
1 / 27

Luc Lebbe , Sarah Jonckheere & Alexander Vandenbohede Department of Geology and Soil Science, - PowerPoint PPT Presentation


  • 144 Views
  • Uploaded on

Modeling of Historical Evolution of Salt Water Distribution in the Phreatic Aquifer in and around the silted up Zwin Estuary Mouth (Flanders, Belgium). Luc Lebbe , Sarah Jonckheere & Alexander Vandenbohede Department of Geology and Soil Science, Ghent University, Gent, Belgium.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' Luc Lebbe , Sarah Jonckheere & Alexander Vandenbohede Department of Geology and Soil Science, ' - dixie


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Modeling of Historical Evolution of Salt Water Distribution in the Phreatic Aquifer in and around the silted up Zwin Estuary Mouth (Flanders, Belgium)

Luc Lebbe, Sarah Jonckheere& Alexander Vandenbohede

Department of Geology and Soil Science,

Ghent University, Gent, Belgium

location of studied area
LOCATION OF STUDIED AREA

Map of Belgium

Studied area

is located

between

Zeebrugge

and

the

Dutch-Belgian

border

slide3
Evolution of Fresh-SaltDiSTRIBUTIOnaround Zwin estuary mouth is modeled for a period of C. five centuries

The Zwin Estuary is the former waterway to

Flemish medieval seaports of

Sluis, Damme and Brugge (Bruges)

During the considered modeling period this estuary silted up and the modeled area changes

from an area around an estuary mouth

over a tidal flat

to a rather complex polder dune area.

slide4
MODELING OF HistoricALevolutiONOF SALT WATER dISTRIBUTIONin and around the silted up Zwin Estuary Mouth
  • Applied software MOCDENS3D (Oude Essink, 1998) and VisualMOCDENS3D (Vandenbohede, 2007)
  • Applied finite-difference grid:

- 70 rows (width of all row = 50 m)

- 88 columns (width of all columns = 50 m)

- 12 layers (thickness of each layer = 2 m)

- angle between north and row direction

is 75° turning to the east

modeled area 4400 m on 3500 m and finite difference grid
Modeled AREA (4400 m on 3500 m) AND FINITE DIFFERENCE GRID

Row direction is parallel to present day low water line

hydraulic parameters
Hydraulic Parameters

Phreatic aquifer is formed by sandy deposits.

Heterogeneity is important.

Horizontal and vertical conductivities are deduced by the performance and the interpretation of three pumping tests (range Kh = 1.5 - 45 m/d, Kh/Kv = 25).

Hydrogeological data base (VMM) is used

to generate the transmissivity matrix

and the vertical leakance matrix.

parameters of solute transport
PARAMETERS OF SOLUTE TRANSPORT
  • Water conductive porosity is 0.38
  • Longitudinal dispersivity is 0.2 m
  • Transversal dispersivity for hor. flow is 0.02 m
  • Transversal dispersivity for vert. flow is 0.01 m
  • Density dependent flow
  • Density of salt water = 1020 Kg/m³
  • Density of fresh water = 1000 Kg/m³
boundary conditions
Boundary CONDITIONS

Boundary conditions on shore and banks of estuary in

uppermost layer depend strongly on the surface elevation.

Therefore the reconstruction of the historical evolution of the surface elevation is very important.

Rech. dunes=280 mm/y

Rech. polders= 28mm/y

W. & E. boundary coincide with flow lines  Impervious boundaries

N. & S. boundary are constant head boundaries

slide9

historiCAL EVOLUTION OF LoCATION AND ELEVATION OF THE SHORE, The ESTUARY BANKS AND THE TIDAL FLATS ARE DEDUCED FROM ONE PAINTING, FOUR OLD MAPS AND THE PRESENT DAY MAP

Basedonwork of Historian Johan Termote (2004) of the

TouristDevelopmentAgency‘Westtoer

Digital Terrain Model (DTM or DEM) is deducedfrom

the abovementioneddocuments

First document is

painting of POURBUS (1571) of the region ‘Brugse Vrije’

Following are fouroldmaps :

Wilschut (1737-1740), Lammeire (1784),

Van der Maelen (1846), De Mey (1880)

and the present day map

Eight stress periods are consideredwith a duration of c. 60 y

purposes of the selected results
PuRposes OF The SeLECTED RESULTS
  • To demonstrate the occurrence of

inverse density distributions under the shores and

the banks of estuaries

  • To demonstrate that the shapes of these distributions

are strongly depended of the slope of the estuary bank

and of the heterogeneity of the phreatic aquifer

  • To demonstrate how these distributions evolve

when entrapped under an area with a small

hydraulic gradient ( e.g. a tidal flat)

slide13
Fresh water head (WHITE contour LinEs) andsalt water percentage (colors) OF Layer 2 During SECOND HALF OF 16th CENTURY
slide14

Fresh water head (WHITE contour LinEs) andsalt water percentage (colors) IN N-S CrOSS SECTION (CoLumn 85, EAST BOUNDARY) During SECOND HALF OF 16th CENTURY

deduced dtm of modeled area first half of 17th century
DEDUCED DTM of MODELED AREA FIRST HALF OF 17th CenTURY

East ward movement of estuary with smaller draft for ships

Decrease slop left estuary bank ; increase slop right estuary bank .

slide16
Fresh water head (WHITE contour LinEs) and salt water percentage (colors) IN Layer 2 AROUND MIDDLE OF 17th CENTURY
slide17

Fresh water head (WHITE contour LinEs) andsalt water percentage (colors) IN N-S CrOSS SECTION (CoLumn 85, EAST M. B.) AROUND MIDDLE OF 17th CENTURY

reconstructed dtm of modeled area in the second half of the 17th century
RECONSTRUCTED DTM of MODELED AREA IN THE SeCOND HALF OF THE 17th CenTURY

East ward movement of estuary which is almost completely silted up

Erosion of eastern dunes

slide19
Fresh water head (WHITE contour LinEs) and salt water percentage (colors) IN Layer 2 AT THE END OF THE 17th CENTURY
slide20

Fresh water head (WHITE contour LinEs) andsalt water percentage (colors) IN N-S CrOSS SECTION (CoLumn 85) AT THE END OF THE 17th CENTURY

deduced dtm of modeled area based on wilschut map 1737 1740
DEDUCED DTM of MODELED AREA BASED ON WILSCHUT MAP (1737-1740)

Eastern dunes fade away and the estuary is changed into a tidal flat

Enlargement of polders by the construction of the Saint Paul’s Dyke

slide22
Fresh water head (WHITE contour LinEs) and salt water percentage (colors) IN Layer 2 During SECOND HALF OF 18th CENTURY
slide23

Fresh water head (WHITE contour LinEs) andsalt water percentage (colors) IN N-S CrOSS SECTION (CoLumn 85) IN THE SECOND HALF OF THE 18th CENTURY

deduced dtm of modeled area based on lammeire map 1784
DEDUCED DTM of MODELED AREA BASED ON LAMMEIRE MAP (1784)

Landward movement of high water line

Western dunes are eroded and shore has a rather large slope .

slide25
Fresh water head (WHITE contour LinEs) and salt water percentage (colors) IN Layer 2 AT THE BEGINNING OF THE 19th CENTURY
slide26

Fresh water head (WHITE contour LinEs) andsalt water percentage (colors) IN N-S CrOSS SECTION (CoLumn 85) IN THE BEGINNING OF THE 19th CENTURY

conclusions
CONCLUSIONS

Tidal fluctuations on the shore and on the banks of the

estuary result in inverse density distributions

Shapes of these inverse density distributions depend on slope

of shore or bank and on the heterogeneity of phreatic aquifer

During silting up of estuaries these inverse distributions became entrapped under the tidal flat area with a very slow GW flow (principally induced by density differences)

Results show very interesting evolutions of inverse density distributions which need more detailled modeling

These evolutions should be modelled more in detail in the future:

– changes from one landscape into another

(in sedimentologically well-founded events)

- influence of discretization of space-time grid on evolutions of inverse density distributions

ad