Hydrogeological Modelling of the Esperance Drinking Water Aquifer Subjected to Seawater Intrusion

• Main Author: Vreeburg, Huib (author)
• Other Authors: van Breukelen, B.M. (graduation committee), Prommer, Henning (graduation committee), Schoups, G.H.W. (graduation committee), Delft University of Technology (degree granting institution)
• Format: Master Thesis
• Language: English
• Published: 2022
• Subjects: groundwater modelling; MODFLOW; PEST++; groundwater abstraction; coastal wetland system; saltwater intrusion; Southern Ocean; Warden
• Online Access: http://resolver.tudelft.nl/uuid:01387dff-ef55-4270-99bb-6ff89b4bf8d2

Saltwater intrusion in groundwater is a concern in many aquifers around the world. It results in deterioration of potable and irrigation water quality and degradation of ecosystems. The problem is exacerbated by fresh groundwater abstraction, drying climates and a rising seawater level. Esperance is a small town situated on the south coast of Western Australia. The drinking water is supplied by a borefield located on the coastal plain in between the Southern Ocean and the saline lakes: Lake Warden and the terminal Pink Lake. Saltwater intrusion has been monitored for over two decades in this aquifer. Managing Saltwater intrusion has been a priority for the local water company and the regulator for decades yet a numerical model of the aquifer capable of quantifying flows and salinity distributions does not exist. In this study, a numerical flow model was developed as a first step towards a model that also includes saltwater movement, i.e. density-dependent flow. A site-specific literature review is documented in this report, as well as relevant saltwater intrusion studies. A 3-dimensional hydrogeological model was created with a kriging geostatistical algorithm with data from Airborne Electromagnetic (AEM) surveys and borehole logs. A database including climatological fluxes, abstraction rates, groundwater heads, lake stages and lithographic data was created. The salinity distribution in the catchment was analysed using borehole observations and AEM data. Groundwater salinity is more prevalent in the east and northeast of the domain. Salts from inland sources are transported to the coastal lakes by a combination of groundwater and surface water. The flow model was calibrated with PEST++ and a linear parameter error and sensitivity reduction was carried out with GENLINPRED from the PEST++ suite. The result of the study is a groundwater flow model that is able to quantify the approximate fluxes and heads within the catchment. However, it must be noted that the calibration can be improved. The relative error ...