Waves induced by ship movement might be harmful for the habitat in the littoral zone of rivers due to the temporally increasing bed shear stress, the high-energy breaking waves and the consequently related detachment of benthic animals. In order to understand the complex hydrodynamic phenomena resulting from littoral waves, we present the testing of a novel methodology that incorporates field observations and numerical tools. The study is performed at a section of the Danube River in Hungary and analyzes the influence of different ship types. The field methods consist of parallel acoustic measurements (using Acoustic Doppler Velocimetry (ADV)) conducted at the riverbed and Large Scale Particle Image Velocimetry (LSPIV) of the water surface. ADV measurements provided near-bed flow velocities based on which the wave induced currents and local bed shear stress could be estimated. The LSPIV was able to quantify the dynamics of the breaking waves along the bank. Furthermore, computational fluid dynamics (CFD) modeling was successfully applied to simulate the propagation and the breaking of littoral waves. The used techniques complement each other well and their joint application provides an adequate tool to support the improvement of riverine habitats.

Turbulent momentum and heat exchanges at the air‐water interface of lakes are complex processes due to diverse characteristics such as climate, fetch limitation, and geometry; however, their parameterizations are necessary for hydro‐ and thermodynamic modeling. In this study, we performed comprehensive research on turbulent exchanges of a shallow, large but highly fetch limited lake employing 5 months of simultaneous eddy‐covariance (EC), wave, energy, and water budget measurements. Based on the Monin‐Obukhov similarity theory, wind and wave age‐related drag coefficients and roughness lengths were derived for very young wave ages. The new drag functions showed an increased water surface resistance compared to marine conditions. In terms of water vapor roughness length and transfer coefficients, an apparent intra‐seasonal variation was observed. Turbulent heat fluxes were evaluated by closing the lake's energy budget using the Bowen ratio method. Furthermore, we aimed to close the energy budget by assuring the water balance closure as well through the evaporation (latent heat flux), resulting in significant deviations from the EC‐based results. EC‐based heat fluxes and transfer coefficients were found to be underestimated on average by 29% and 33%, respectively. The water balance closure suggested that the energy residual should not be distributed based on the Bowen ratio, and sensible heat fluxes were more underestimated than latent heat fluxes. In the case of Lake Balaton, atmospheric stability plays a minor role; however, our analysis revealed significant effects caused by the surrounding topography and water side stratification.

The temporal alteration of the hydrodynamic regime in rivers due to navigation has significant effects on riverine ecosystems. Most of the key mechanisms and interactions between hydrodynamic and ecological variables have already been revealed; however, the quantitative evaluation of biotic and abiotic variables still stands a challenge. This paper aims to present a thorough, spatiotemporal framework, involving field and computational tools, for the assessment of wave hydrodynamics in the littoral zone of rivers, where its ecological relevance is the most significant. The temporal variation of significant wave heights is derived from high‐frequency pressure measurements, offering a well‐comparable statistical evaluation of individual wave events considering the duration of different wave intensities. Acoustic Doppler velocimetry (ADV) is used for the assessment of near‐bank velocities, from which the secondary wave‐related components have been filtered offering relevant validation data for numerical modelling. The small footprint of the ADVs is extended with up‐to‐date computational fluid dynamics modelling. Wave spectra derived from the pressure measurements are used as boundary conditions for phase‐resolved irregular wave modelling with the level set method based numerical model REEF3D. The properly validated model offers the assessment of the most relevant hydrodynamic variables (e.g., velocity or turbulent kinetic energy) in a spatially extended manner, from which the hydrodynamic footprint of the wave events can be interpreted in a statistical fashion. The implementation of the proposed framework is illustrated through a case study at a Hungarian section of the Danube River.

Chaotic motion of particles in fluid flows was recognised decades ago but this phenomenon has only been acknowledged recently in civil engineering. Herein it is shown that chaotic advection has a wide range of important hydraulic and environmental applications. The most important characteristics of chaotic particle transport, such as the filamentary (fractal) distribution of advected particle ensembles and their importance for active chemical or biological processes, which has far-reaching ecological or environmental consequences, are reviewed. An important tool to discover and describe the filamentary distribution is the finite-size Lyapunov exponent. As a particular example, its application to an idealised shallow, wind-driven lake is presented. It is shown that the finite-size Lyapunov exponent provides a useful tool to investigate, for example, the spatial distribution of pollution in the lake – it can help to determine the most exposed shore segments and identify effectively mixed or stagnant regions in the lake.