Modelling the influence of the Abu Nakhla pond on the phreatic aquifer in Qatar

173 Pages·2015·9.14 MB·English

by  Joren De Tollenaere

FACULTEIT WETENSCHAPPEN
Opleiding Master of Science in de geologie

Modelling the influence of the Abu Nakhla pond
on the phreatic aquifer in Qatar:
present and future scenarios

Joren De Tollenaere
Academiejaar 2014–2015

Scriptie voorgelegd tot het behalen van de graad
Van Master of Science in de geologie

Promotor: Prof. Dr. L. Lebbe
Leescommissie: J. Claus, Prof. Dr. V. Cnudde

VOORWOORD
Eerst en vooral wil ik m’n promotor prof. dr. Lebbe bedanken voor de mogelijkheid om dit
onderwerp als masterproef te doen. Ook wil ik hem bedanken voor zijn verhelderende
uitleg over de resultaten van de modellen en over de hydrogeologie. Ik wil ook Jasper
Claus bedanken voor het gebruik van zijn python scripts om de input van de modellen te
maken alsook voor zijn inzicht en aanpassingen aan het model. Gert-Jan Devriese wil ik
bedanken voor de morele steun en voor het gebruik van zijn bureau waar we vele leuke
uren hebben doorgebracht. En als laatste wil ik Devlin Depret bedanken voor zijn rationele
benadering in het steunen bij het schrijven van deze masterproef en zijn kritisch inzicht
inzake de resultaten.

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Table of contents

1. INTRODUCTION ......................................................................................................... 1
2. STUDY AREA ............................................................................................................. 3
3. GEOLOGY .................................................................................................................. 5
3.1 Structural geology .................................................................................................. 5
3.2 Surface geology ..................................................................................................... 5
3.3 Stratigraphy ........................................................................................................... 6
3.3.1 Umm er Radhuma Formation .......................................................................... 7
3.3.2 Rus Formation ................................................................................................. 7
3.3.3 Dammam Formation ...................................................................................... 10
3.3.4 Dam Formation ............................................................................................. 11
3.3.5 Hofuf Formation ............................................................................................ 11
3.3.6 Sabkhas ........................................................................................................ 12
4. HYDROGEOLOGY ................................................................................................... 13
4.1 General hydrogeology .......................................................................................... 13
4.2 Head distribution .................................................................................................. 14
4.3 Hydrogeological parameters ................................................................................ 19
4.4 Fresh and salt water distribution .......................................................................... 20
5. CLIMATE AND HYDROLOGY .................................................................................. 23
6. MODELLING SOFTWARE ....................................................................................... 29
6.1 Evolution of the modelling software ...................................................................... 29
6.2 MODFLOW .......................................................................................................... 29
6.2.1 Code concepts .............................................................................................. 30
6.2.2 Discretisation of the groundwater reservoir .................................................... 30
6.2.3 Finite difference approximation of the groundwater flow ................................ 32
6.2.4 Iteration with the Strongly Implicit Procedure ................................................. 34
6.2.5 Cell and boundary types ................................................................................ 35
6.3 MOC3D................................................................................................................ 36
6.4 MOCDENS3D ...................................................................................................... 37
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6.5 Packages............................................................................................................. 38
6.5.1 MODFLOW packages ................................................................................... 38
6.5.1.1 Basic package (.bas-file) ........................................................................................ 38
6.5.1.2 Block-Centred-Flow package (.bcf-file) .................................................................. 39
6.5.1.3 Well package (.wel-file) .......................................................................................... 40
6.5.1.4 Evapotranspiration package (.evt-file) ................................................................... 41
6.5.1.5 Strongly Implicit Procedure package (.sip-file)....................................................... 41
6.5.1.6 Name file (Infile.nam) ............................................................................................. 41
6.5.2 MOCDENS3D packages ............................................................................... 42
6.5.2.1 MOC package (.moc-file) ....................................................................................... 42
6.5.2.2 Densin.dat-file ........................................................................................................ 42
6.5.2.3 Name file (moc.nam) .............................................................................................. 42
7. MODEL CONSTRUCTION ....................................................................................... 43
7.1 Base model ......................................................................................................... 43
7.1.1 Location and discretisation of the study area ................................................. 43
7.1.2 Hydrogeological parameters ......................................................................... 46
7.1.3 Boundary conditions and initial head values .................................................. 48
7.1.4 Fresh and salt water distribution .................................................................... 51
7.1.5 Recharge ...................................................................................................... 53
7.1.6 Evapotranspiration ........................................................................................ 53
7.1.7 Time discretisation and closure criterion ....................................................... 54
7.2 Adding the pond into the base model ................................................................... 54
7.2.1 Sub-model one: Steady state flow with pond ................................................. 55
7.2.1.1 Discretisation of the Abu Nakhla pond ................................................................... 55
7.2.2 Sub-model two: Mimicking steady state with an unsteady state model .......... 57
7.2.2.1 Hydrogeological parameters .................................................................................. 58
7.2.2.2 Time discretisation and closure criterion ................................................................ 60
7.2.3 Sub-model three: From mimicking steady state to full unsteady state ........... 61
7.2.3.1 Boundary conditions and storage factors ............................................................... 61
7.2.3.2 Time discretisation and closure criterion ................................................................ 61
7.2.4 Sub-model four: Desiccation and dissipation of the Abu Nakhla pond ........... 62
7.2.4.1 Boundary conditions and hydrogeological parameters .......................................... 62
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7.2.4.2 Time discretisation and closure criterion ................................................................ 62
7.3 Sensitivity analysis ............................................................................................... 63
7.3.1 Horizontal conductivity of the upper aquifer ................................................... 63
7.3.2 Vertical conductivity of the gypsiferous Rus Formation .................................. 63
7.3.3 Storage factors .............................................................................................. 64
8. RESULTS AND DISCUSSION .................................................................................. 65
8.1 Base model .......................................................................................................... 65
8.1.1 Steady state flow ........................................................................................... 65
8.1.2 Unsteady state flow ....................................................................................... 66
8.2 Desiccation of the Abu Nakhla pond .................................................................... 68
8.2.1 Sub-model one: Steady state flow with pond ................................................. 68
8.2.2 Sub-model two: Mimicking steady state with an unsteady state model .......... 69
8.2.3 Sub-model three: From mimicking steady state to full unsteady state ............ 71
8.2.4 Sub-model four: Desiccation and dissipation of the Abu Nakhla pond ........... 73
8.3 Sensitivity analyses ............................................................................................. 79
8.3.1 Horizontal conductivity of the upper aquifer ................................................... 79
8.3.2 Vertical conductivity of the gypsiferous Rus Formation .................................. 88
8.3.3 Storage factors .............................................................................................. 97
8.3.3.1 Storage factor near the water table ........................................................................ 97
8.3.3.2 Storage factor of the aquifer ................................................................................. 106
8.4 Discussion ......................................................................................................... 114
9. CONCLUSION ........................................................................................................ 123
10. NEDERLANDSTALIGE SAMENVATTING ........................................................... 127
11. REFERENCES ...................................................................................................... 133
APPENDIX A: BOREHOLE LOGS ............................................................................. 137
APPENDIX B: TIME DISCRETISATION ..................................................................... 154

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List of figures
Figure 1: Location of Abu Nakhla in Qatar (Google Earth) ............................................... 3
Figure 2: Evolution of the Abu Nakhla pond from 1972 to 2009 (ESC Archives). ............. 4
Figure 3: Location of geological structures and surface geology in Qatar (Al-Saad, 2005).
........................................................................................................................................ 5
Figure 4: Stratigraphy and lithology of the Eocene sediments in Qatar (Al-Saad, 2005). . 6
Figure 5: The depositional facies of the Rus Formation in Qatar (Eccleston, et al., (1981)
modified by Elobaid) ........................................................................................................ 9
Figure 6: Head distribution in the Umm er Radhuma Formation aquifer of Qatar (Lloyd, et
al., 1987). ...................................................................................................................... 15
Figure 7: Head distribution in the Rus Formation aquifer of Qatar (Lloyd, et al., 1987). . 16
Figure 8: Head distribution in the Dammam Formation aquifer of Qatar (Alsharhan, et al.,
2001). ............................................................................................................................ 17
Figure 9: Potentiometric surface map in meter amsl of Qatar based on results from April
2009 (Schlumberger, 2009). .......................................................................................... 18
Figure 10: Total Dissolved Solids (TDS) isoconcentration map in ppm (Schlumberger,
2009). ............................................................................................................................ 21
Figure 11: Total annual rainfall (mm yr-1) of Qatar from 1972 to 2005 (Amer, et al., 2008).
...................................................................................................................................... 23
Figure 12: Average annual total rainfall (mm yr-1) between 1989 and 2007 (Schlumberger,
2009). ............................................................................................................................ 24
Figure 13: A hypothetical discretised aquifer system with five rows, nine columns and five
layers (McDonald & Harbaugh, 1988). .......................................................................... 31
Figure 14: Block-centred finite difference cells (McDonald & Harbaugh, 1988). ............. 31
Figure 15: Flow into cell i, j, k from cell i, j-1, k (McDonald & Harbaugh, 1988). ............. 33
Figure 16: Discretised aquifer showing boundaries and cell designations (McDonald &
Harbaugh, 1988). .......................................................................................................... 35
Figure 17: Discretisation of the simulation time in stress periods and time steps including
the formulas to calculate the first time step and the following steps (McDonald & Harbaugh,
1988). ............................................................................................................................ 39
Figure 18: Volumetric evapotranspiration Q as a function of head h, in a cell where d is
ET,
the extinction depth and h the ET surface elevation (McDonald & Harbaugh, 1988). ... 41
s
Figure 19: A georeferenced Google Earth image visualising the study area with a large
grid (1 km x 1 km cells) and the normal grid (100 m x 100 m cells). .............................. 44
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Figure 20: Potentiometric surface map of Qatar with the study area visualised as the black
rectangle (Schlumberger, 2009). ................................................................................... 48
Figure 21: Cross-section through Qatar with the different hydrogeological units with their
respectively TDS values (Harhash & Yousif, 1985). ...................................................... 52
Figure 22: Overview of the different sub-models with the input and output used. .......... 55
Figure 23: Picture of the water level of the Abu Nakhla pond on 8 May 2015 measuring
35.10 m amsl. ............................................................................................................... 56
Figure 24: Boundary conditions for sub-model one. 1 are the active cells, -1 are the
constant-head cells with TDS 3,000 ppm from the Dammam and upper Rus Formation
aquifer and -4 are the constant-head cells with TDS 2,000 ppm from the Abu Nakhla pond.
..................................................................................................................................... 56
Figure 25: Interpolated initial heads of each layer of sub-model one. ............................ 57
Figure 26: Visualisation of the raster file with the bathymetry of the Abu Nakhla pond with:
(1) Light green is the A basin with interpolated values, (2) Dark blue is the B basin with
interpolated values, (3) Red is the C Basin with no direct measurements and is put at 33
m, (4) Light blue are manually interpolated cells with their neighbour and (5) Purple are
the cells surrounding the pond with values set at 32 m. ................................................ 59
Figure 27: Visualisation of the measured bathymetry lines with their spatial variability, used
for the interpolation for the bottom of the Abu Nakhla pond. .......................................... 60
Figure 28: Horizontal cross-section of the groundwater head (m) through layer five of the
steady state flow base model, stress period five. .......................................................... 66
Figure 29: Horizontal cross-section of the groundwater head (m) through layer five of the
unsteady state base model, stress period fifteen. The dark red colour in the upper left
corner represents inactive cells. .................................................................................... 67
Figure 30: Vertical cross-section of the groundwater head (m) along row 10 of the unsteady
state base model, stress period fifteen. The dark red colour represents inactive cells. .. 67
Figure 31: Vertical cross-section of the groundwater head (m) along row 71 of the unsteady
state base model, stress period fifteen. The dark red colour represents inactive cells. .. 68
Figure 32: Horizontal cross-section of the groundwater head (m) through layer one of sub-
model one, stress period five. ....................................................................................... 69
Figure 33: Vertical cross-section of the groundwater head (m) along row 71 of sub-model
one, stress period five. .................................................................................................. 69
Figure 34: Horizontal cross-section of the groundwater head (m) through layer one of sub-
model two, stress period fifteen. The blue colour represents dry cells. .......................... 70
Figure 35: Horizontal cross-section of the groundwater head (m) through layer five of sub-
model two, stress period fifteen. The dark blue colour in the upper left corner represents
dry cells......................................................................................................................... 71
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