RIVER RESEARCH

Water Transport

In our flowing waters, the flow of water is of central importance. Water flows downstream in its riverbed, driven by gravity. The water depth and flow velocities depend on the roughness of the riverbanks and bed, the bed slope, and the cross-sectional geometry. Except for straight channels with a uniform cross-section, where the flow can be considered quasi one-dimensional, rivers typically exhibit complex three-dimensional flow patterns. The flow is mostly turbulent, except for shallow water zones with little flow or areas that are heavily dammed. The turbulent flow exerts shear and pressure forces on its boundaries. Turbulent flow is also responsible for mixing processes and the distribution of dissolved substances and suspended solids, as well as the transport of bedload, plastics, and much more in the river system.

Sediment Transport – Bedload and Suspended Load

The sediment budget and sediment connectivity of rivers play a central role in the morphology and functionality of water bodies. However, the dynamic equilibrium of sediment transport, relocation, and sedimentation is often disturbed by the construction of bedload barriers, weirs, reservoirs, and river regulations for flood protection and the use of rivers as waterways, leading to well-known negative consequences for ecology and (protective) hydraulic engineering. Natural measurement data are of fundamental importance to identify the impacts of interventions and to develop suitable measures based on an expanded understanding of processes.

The quantity and composition of transported sediment (bedload and suspended load) are subject to strong temporal and spatial variability and depend not only on hydraulic conditions but also on availability, among other factors. Capturing the transport is associated with many challenges that require innovative approaches and measurement methods. At the IWA, extensive long-term monitoring is carried out at several stations in cooperation with the Hydrographic Services and Ministries (BML, BMK), ranging from steep mountain streams to the Danube. This allows for the investigation of transport processes, and the data obtained can be used for the application, calibration, and further development of transport formulas and numerical models.

Conceptualization of Solid Management Concepts

Sustainable and resilient approaches to managing our rivers require the development of comprehensive solid management concepts. These concepts include strategies and methods for capturing, analyzing, and controlling sediments with the aim of better understanding and effectively managing the impacts of erosion, sedimentation, and other geomorphological processes. In addition to natural measurement data on bedload and suspended load, geomorphological surveys in the catchment area are also of great importance. The use of drones, cameras, and LiDAR sensors in the field can yield high-resolution data on sediment volumes and morphological structures, enabling the creation of precise three-dimensional models. These innovative technologies provide valuable insights into sedimentation behavior in retention areas, dynamic flow processes, and potential changes in the river course.

Transport of Micro and Macroplastics

The triumph of plastic as a material, due to its versatile applications and resistance, continues unabated; in 2020, 20kg of plastic was produced for every person living on Earth. Due to its durability and the fact that only a small proportion is recycled or incinerated worldwide, most plastic remains in our environment. If not at least properly disposed of, it can enter our food chain through various pathways and be ingested by humans. To improve the situation, research on possible transport routes, major entry paths, and methods for concentrated removal of plastic from the environment is necessary.

Therefore, the IWA has been researching for several years to quantify and characterize plastic transport in our flowing waters. The goal is to identify the main sources responsible for the transport and ultimately reduce or prevent further entry. Research on this topic has been conducted on the Danube, in the Austrian Alps, in Vietnam, and on one of Europe’s most polluted rivers, the Ishem River in Albania.

Transport of Nutrients / Pollutants

Rivers have an outstanding ability self-purification through physico-chemical and biological processes. However, the interaction of microbiological activities, plants and aquatic organisms such as macroinvertebrates and fish are in a delicate balance that can be disturbed by external influences. Causes of disruption include the release of pollutants from industry, mining and transport, as well as the entry of medicines and personal care products. The complex entry paths (point sources, dry and wet deposition), in combination with climate change, are causing increased societal problems. Biodiversity loss and the threat to drinking water supply and food safety are the consequences.
IWA investigates the challenges of particle-bound pollutant transport in the context of river morphology as a boundary for the maintenance and restoration of self-cleaning processes. The aim is an improved process understanding of particle-bound pollutant transport in rivers. The research will contribute to the United Nations Sustainable Development Goals: “Clean Water and Sanitation”, “Sustainable Cities and Communities” and “Life below Water”.

Interaction of Rivers and Vegetation

During higher flows, vegetation on floodplains and, increasingly due to river restoration projects, on sediment banks within the channel comes into contact with the flow and sediment transport. Vegetation increases the hydraulic roughness of inundated areas and thus influences the flow, water levels, and retention effect of runoff areas, making it particularly relevant for flood protection issues. Vegetation also affects sediment transport and can thus influence morphological development, upon which many functions of flowing waters depend. Specifically, the effect of flexible vegetation, which occurs particularly near banks under given habitat conditions and therefore often interacts with the flowing water and transported sediments, poses a challenge in calculations. The large flows in the hydraulic laboratory of the IWA allow for experiments on plant deformation and sediment transport on a 1:1 scale. In comparison with measurements in the laboratory and in nature, computer models are developed at the IWA (e.g., a finite element model for modeling plant deformation and dynamic roughness) and coupled with hydrodynamic-numerical models and sediment transport models to improve the predictability of morphological changes and flood impacts considering vegetation.

Socioeconomic Aspects

In addressing research questions, the IWA pursues integrative approaches that promote close collaboration and exchange with various scientific disciplines and relevant stakeholders. Particular emphasis is placed on the involvement of different stakeholder groups to bring diverse perspectives and expertise into the research process. This enables comprehensive analysis and solution development that considers scientific findings as well as practical, societal, and ecological requirements. The interdisciplinary dialogue and networking with external partners thus contribute significantly to the quality and relevance of the research outcomes.