Density waves inhibit the stability of (long) pipelines, which cannot be predicted using current day design tools. Density waves are formed due to an inverse relationship between sand eroding and settling in a pipeline. By designing and building a dedicated flow loop, an experimental study on how the erosion and sedimentation of sand in a pipe is influenced by particle size and concentration is conducted. Moreover, it is determined whether the erosion and sedimentation process can be modeled numerically using existing analytical pick-up functions. This could be applied for predicting density waves in horizontal pipelines.
From the experimental study it is found that at higher concentrations, the caterpillar-like movements of the bed, associated with the sedimentation and erosion unbalance at high concentrations, were observed more and more frequently. The influence of the mean grain size diameter can be characterised as the ability of the mixture to trigger amplifying density waves in the horizontal measurement section. Only the coarser sands used in the experiments were found to experience the sliding-stopping behaviour. Implementing different analytical pick-up functions to simulate the experimental study resulted in sufficiently accurate results. Depending on the pick-up function on how much calibration was required the measurements could be simulated adequately.

In Chile, the Biobío river separates the cities of Concepción and San Pedro de la Paz. Bridges crossing the Biobío river ensure a fast and dependable connection, which contributes to the transport options in the region. With the Biobío region being the second largest contributor to the country's GDP, an unreliable transport network is highly undesirable. However, this is exactly what happened since 2016. Some of the bridges crossing the river collapsed, excessive local pier scour near the foundation and negative effects of morphological dynamics were deemed to be one of the causes. Furthermore, Chile is prone to earthquakes and the resulting tsunamis, which can also damage the structural integrity of the bridge. The Chilean Railroad Agency (EFE) wants to realise a new railroad bridge crossing the Biobío river in Concepción, replacing the existing century old railway bridge. To prevent the failure of the new railway bridge, which can result in unnecessary economic damages, the morphological influence and damages due to scour, earthquakes and tsunamis, must be thoroughly understood and modelled. This process of modelling the current and future situations of the Biobío river is part of this project, using Delft3D-FLOW and NeoWave as modelling agents. With the outcomes the programme of requirements and the preliminary design for the bridge are updated and presented.