Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Accueil du site → Master → Pays Bas → 2019 → Isotopic tracing and numerical modelling of saline groundwater discharge into Matola Wetlands, Mozambique

UNESCO-IHE Institute for Water Education, Delft (2019)

Isotopic tracing and numerical modelling of saline groundwater discharge into Matola Wetlands, Mozambique

Delwar, Rezwana Binte

Titre : Isotopic tracing and numerical modelling of saline groundwater discharge into Matola Wetlands, Mozambique

Auteur : Delwar, Rezwana Binte

Université de soutenance : UNESCO-IHE Institute for Water Education, Delft

Grade : Master of Science (MS)

Résumé partiel
Population pressure, repeated natural disasters and sea-level rise associated with projected climate changes increase pressure on secure freshwater resources, notably on groundwater of the coastal areas such as the Great Maputo Area in Mozambique. The Matola River, located in the west of Maputo, is a perennial river that carries mostly brackish/saltwater originating from groundwater seepage and salinity makes the river water unusable. The main origin of the saline groundwater is assumed to be fossil seawater, entrapped in the silty marl and clay dominated aquitards for thousands of years. However, detailed studies about the salinity problem of coastal Maputo city, particularly of Matola River are very limited. This research focuses on the integration of regional hydrogeochemistry, isotopic analysis and groundwater flow models to trace the source and evolution of saltwater in Matola wetlands. The Piper plot, Stiff map and bivariate diagrams of major ions reveal salinization through mixing with seawater followed by ion-exchange as the prominent hydrochemical processes of the study area west of the Matola River. On the other hand, east of the Matola River the dominant process seems to be freshening, and this distribution is related to land cover connected recharge rates of the area and the hydraulic properties of the aquitards. Water stable isotopes (δ2H, δ18O) and 18O/Cl further confirm the mixing process between fresh and connate saline groundwater in conjunction with evaporation of shallow groundwater and surface water being the major sources of salinity. The advective transport model was developed in PMWIN based on the existing steady-state model to examine the residence time and flow paths of the groundwater, particularly for the area of Matola River and wetlands. The existing steady-state model shows the highest sensitivity to effective porosity, followed by hydraulic conductivities and model geometry. The range of travel times obtained through particle tracking was frequently large and highly dependent on the number of particles. Using the result of 13C/14C (DIC) isotopes, the evaluation of the existing groundwater flow model was undertaken.

Sujets  : saline water groundwater discharge numerical modelling hydrochemistry wetlands Mozambique

Présentation et version intégrale

Page publiée le 1er avril 2021