Coupled flow and salinity transport modelling in semi-arid environments: The Shashe River Valley, Botswana

Peter Bauer-Gottwein, R.J. Held, S. Zimmermann, F. Linn, W. Kinzelbach

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Numerical groundwater modelling is used as the base for sound aquifer system analysis and water resources assessment. In
many cases, particularly in semi-arid and arid regions, groundwater flow is intricately linked to salinity transport. A case in
point is the Shashe River Valley in Botswana. A freshwater aquifer located around an ephemeral stream is depleted by the
combined effect of transpiration and pumping. Quantitative system analysis reveals that the amount of water taken by
transpiration is far more than the quantities pumped for water supply. Furthermore, the salinity distribution in and around
Shashe River Valley as well as its temporal dynamics can be satisfactorily reproduced if the transpiration is modelled as a
function of groundwater salinity. The location and dynamics of the saltwater–freshwater interface are highly sensitive to the
parameterization of evaporative and transpirative salt enrichment. An existing numerical code for coupled flow/transport
simulations (SEAWAT) was adapted to this situation. Model results were checked against a large set of field data including
water levels, water chemistry, isotope data and ground and airborne geophysical data. The resulting groundwater model was
able to reproduce the long-term development of the freshwater lens located in Shashe River Valley as well as the decline in
piezometric heads observed over the last decade. Furthermore, the old age of the saline water surrounding the central freshwater
lens could be explained.
Original languageEnglish
JournalJournal of Hydrology
Volume316
Pages (from-to)163-183
Publication statusPublished - 2006

Keywords

  • Evapotranspiration
  • Salinity
  • Okavango Delta
  • Groundwater modelling
  • Aquifer management

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