1. Promoting Groundwater Cooperation in Southern Africa through Modeling: the Stampriet Transboudnary Aquifer System (STAS) case study
Piet Kenabatho, Bertram Swartz, Sivashni Naicker, Marc Leblanc,
Clément Berry, Tales Carvalho Resende
1st SADC Groundwater Conference
27 September 2018
Johannesburg, South Africa

2. The Stampriet Transboundary Aquifer System (STAS)
The STAS lies entirely within the Orange-Senqu River Basin.
The STAS covers a total area of km² (73% of the area in Namibia, 19% in Botswana, and 8% in South Africa).
The STAS is a large farming area with approximately 1200 farms (mostly in Namibia), out of which 80 are irrigation farms
Groundwater use: 52% irrigation, 32% stock watering, 16% domestic use
No mining and industrial activities
Area lightly populated (approximately inhabitants)
Annual groundwater abstraction: 20Mm3 (around 70% in the Stampriet area)
Precipitation: from 150 to 300 mm/yr

3. The GGRETA project
Governance of Groundwater Resources in Transboundary Aquifers (GGRETA) project:
Funded by the Swiss Agency for Development and Cooperation (SDC)
Implemented by UNESCO International Hydrological Programme (IHP)
Phase 1 ( ): In-depth assessment of the STAS
Phase 2 ( ):
Capacity-building modules on groundwater modeling, legal and institutional, and gender issues
Development of the STAS numerical model
Set the baseline for institutionalizing cooperation over the STAS

4. Background
Main objective: Develop a numerical model for the STAS aquifer to fill existing gaps
Modelling exercise started under FREEWAT platform (open source and free). However, the platform revealed to lack some robustness.
Early 2018: Decision to change the software that is being used to ModelMuse (in cooperation with the University of Avignon)
University of Avignon: Coordinator of the UNESCO-IHP programme on Groundwater and Climate Change (GRAPHIC)
Advantages of ModMuse:
Free software that calls ModFlow (
Same software that is being used in the Ramotswa modelling exercise

5. PREPARATION OF THE MODEL
Timeframe
PREPARATION OF THE MODEL
CAPACITY BUILDING
Objective: Support
Policy
October 2018 – December 2018
Final simulations and results
(participatory approach)
September 2018
National trainings tailored to the needs of each country
May 2018 – September 2018
Definition of scenarios and preliminary simulations (participatory approach)
May 2018:
Transient state calibration
April 2018:
Steady state calibration
March 2018: Presentation of advancements + Revision of model geometry
February 2018: Start of modelling exercise under ModelMuse

6. - Numerical modelling exercise -

7. University of Avignon
Collaborating with UNESCO-IHP since 2009 under the UNESCO-IHP programme on Groundwater and Climate Change (GRAPHIC)

8. Definition of the model grid
Active cell size :
/ m
- Around 5000 active cell
Area : Km²
Aquifers: Kalahari, Auob, Nossob
Aquitards: Rietmond, Mukorob
Top view of the STAS grid.
Kalahari
Rietmond
Auob
Mukorob
Nossob

9. Boundary conditions CHD North & South
Zero flux limit
Constant Head
CHD North & South
- Kalahari : interpolation of piezometric data
- Auob : Aquifer wall + 15 m
- Nossob : Aquifer wall + 10 m
East & West boarders : Zero flux limit
Constant Head

10. Steady State Calibration
Configuration
Discharge area (5mm/years)
Uniform recharge (4mm/years)
Kx calibration
Aquifer : discretization
Aquitard : homogeneous (1E-6 m/days)
Ky = Kx
Kz = Kx/10

11. Kx (m/days)
Result of the hydraulic conductivity on the stampriet aquifer for the Kalahari, Auob and Nossob for the second configuration.

12. Steady state simulation results
Global RMS (28m)
Result of the steady state simulation on the stampriet aquifer for the Kalahari, Auob and Nossob showing the heads values for the second configuration.

13. Transient Simulation Initial condition : Time step: Storage parameter:
Start with steady state
Time step:
Time start in 1978, time end in 2016
Discretization : each days ( ), month (456) or years (38)
Storage parameter:
Ss for confined aquifer : 0.001
Sy for unconfined aquifer : 0.15
Pumping Rate:
Livestock = Kalahari
Domestic + irrigation = Auob & Nossob
Prosopis = 50L/Day for 1 tree

14. Transient MODFLOW settings
Time step : each years (could be modified)
38 years ( )
Modflow Package used for the model
Newton Solver : made for large areas and unconfined aquifer
Implementation of Ss & Sy

15. Transient simulation results
Global RMS (9m)

16. Important interactions between aquifers and aquitards
Scenario 1
Pumping rate x2 :
Simulation until 2066
Auob fed by the Kalahari
Nossob fed by Auob
Important interactions between aquifers and aquitards
Kalahari water budget ; Time : 50 years 
Units : m3/years
Auob water budget ; Time : 50 years
Units : m3/ years
Nossob waterbudget ;
Time : 50 years 

17. The STAS dries little by little
Scenario 2
Pumping rate x10 :
Simulation until 2066
Kalahari begins to dry
Auob and Nossob are not fed anymore
Global recharge becomes too little with regards to pumping
The STAS dries little by little
Kalahari water budget ; time : 50 years ; units : m3/ years
Auob water budget ; time : 50 years ; units : m3/ years
Nossob water budget ; time : 50 years ; units : m3/ years

18. Implications for the Auob and Nossob aquifers
Scenario 3
Recharge decreased by 2 :
Simulation until 2066
Considerable lack of water in the Kalahari
Implications for the Auob and Nossob aquifers
Kalahari water budget ; time : 50 years ; units : m3/ years
Auob water budget ; time : 50 years ; units : m3/ years
Nossob water budget ; time : 50 years ; units : m3/ years

19. A good management of prosopis is essential
Scenario 4
10% increase of prosopis every year:
Simulation until 2066
Considerable implications for the Kalahari
A good management of prosopis is essential
Kalahari water budget ; time : 50 years ; units : m3/ years
Auob water budget ; time : 50 years ; units : m3/ years
Nossob water budget ; time : 50 years ; units : m3/ years

20. The STAS dries up quickly and in an irreversible manner
Scenario 5
Combination of all previous scenarios
The STAS dries up quickly and in an irreversible manner
Kalahari water budget ; time : 50 years ; units : m3/ years
Auob water budget ; time : 50 years ; units : m3/ years
Nossob water budget ; time : 50 years ; units : m3/ years

21. Conclusions and way forward
Considering the existing data and knowledge gaps, simulation results need to be considered with caution.
However, they can already provide interesting pointers for decision-makers.
Current status: good baseline for further developing/improving the model.
How?
More climatic data,
Better defining recharge/discharge area,
Refinement of the grid and geometry of the aquifer.
Way forward:
Simulation of new scenarios,
Trainings to Country Representatives for the utilization/further development of the model.

22. Thank you for your attention t.carvalho-resende@unesco.org