EngD Position at University of Twente

The Haringvliet Estuary in the western part of the Netherlands was closed off in 1970 by a series of locks as part of the Delta Works for coastal protection. After the closure, the Haringliet became a freshwater body and was used as a source of freshwater for consumption and agriculture. Since 2018, the operating policy of the Haringvliet locks has changed and some locks are opened not only to discharge the river to the sea but also to allow limited inflows from the sea during flood tides to enhance the ecosystem functions of the estuary. The incoming saltwater should ideally be flushed out during the subsequent ebb tide. However, the Haringvliet Estuary has several bathymetric depressions that can store large amounts of saltwater, which, depending on the flow conditions, may not mix easily with the freshwater pulses due to the density differences. In such cases, the freshwater flows over the saltwater for extended periods of low river discharge and the flushing of the saltwater from the scour holes may occur in undesirable periods (e.g., due to wind-driven flow recirculation when the locks are closed), affecting the freshwater intakes.

This EngD project will investigate the mixing processes between saltwater that is trapped in large bathymetric depressions and freshwater that flows towards the depression, with the Haringvliet Estuary as a case study. The aim of the project is to determine the flow conditions that lead to flushing of the trapped saltwater from the bathymetric depressions in the Haringvliet Estuary and design a strategy accordingly. The study will be carried out by means of numerical modelling (Delft3D and/or OpenFOAM, depending on the scale of the problem) and by analyzing existing ADCP and CTD measurements, which have been carried out by Rijkswaterstaat and the University of Twente. This project will be part of the SALTISolutions programme, which includes many partners from academia, knowledge institutions, consultancy, and governmental organizations.

The EngD researcher will be based at the Marine and Fluvial Systems (MFS) group at the Department of Civil Engineering of the Faculty of Engineering Technology of the University of Twente (UT).