PhD Defence Lieke Lokin | Understanding and forecasting low flow river dune dynamics in a highly engineered lowland river

Understanding and forecasting low flow river dune dynamics in a highly engineered lowland river

Lieke Lokin is a PhD student in the department Marine and Fluvial Systems. (Co)Promotors are prof.dr. S.J.M.H. Hulscher, dr. J.J. Warmink and dr.ir. A. Bomers from the faculty of Engineering Technology.

This theses aims to better understand river dune dynamics and make steps into forecasting these river dunes, particularly under low to median flow conditions in navigable rivers. This was done through analysis of the dunes in (bi-weekly) bed elevation measurements of the Waal River in The Netherlands. During low flow periods, when sediment transport is small, dunes tend to be longer and flatter but still move 2 to 3 meters per day. During low flow periods dune propagation shifts from advective to more diffusive due to the increased impact of gravity over flow drag. Also, the impact of different dredging techniques on river dune development was studied. While dredging reduces dune heights initially, it does not significantly affect overall dune behavior in time.

The observed dunes were simulated in a dune development model. First idealized dunes were modelled with different sediment transport models. Incorporating gravitational slope effects and suspended sediment transport, helped achieve more realistic dune shapes, particularly in terms of dune height and slope angles. Average dune shapes and propagation of a single idealized dune can be simulated well with the model, but predicting the exact height and location of the highest dune in the river bed requires a different approach. Therefore, secondly, the potential of using the dune development model for forecasting was tested. By adjusting the model for predicting the development of a train of dunes, we show that the development of the highest dune can be simulated well.

In conclusion, the study highlights that river dunes remain mobile and can be effectively modeled to assist in managing navigation and dredging operations, yet emphasizes the need for detailed modeling and optimizing dredging strategies to achieve more significant impacts on river dune dynamics in the shipping lane.