The use of echo-levels from Acoustic Doppler Current Profiler (ADCP) recordings has become more and more common for estimating suspended bed-material and wash loads in rivers over the last decade. Empirical, semi-empirical and physical-based acoustic methods have been applied in different case studies, which provided relationships between scattering particles features derived from samples (i.e., concentration and grain size) and corresponding backscattering strength and sound attenuation. These methods entail different assumptions regarding sediment heterogeneity in the ensonified volume (e.g., particle size distribution (PSD) and spatial concentration gradient). Our work was to compare acoustic backscatter and attenuation properties of suspended sediments, sampled in the rivers Parana and Danube that represented rather different hydro-sedimentological conditions during the surveys. The Parana represents a large sandy river, characterized through a huge watershed and the typical bimodal PSD of sediment in suspension, while the Danube represents in the investigated reach an exposed sand-gravel bed and clay-silt particles transported in the water column in suspension. Sand and clay-silt concentrations clearly dominate the analyzed backscattering strength in the rivers Parana and Danube, respectively, with an effect of PSD level of sorting in the latter case. This comparison clarifies the extent of assumptions made, eventually advising on the actual possibility of applying certain ADCP methods, depending on the expected concentration gradients and PSD of suspended sediment to be investigated.

Knowledge of sediment dynamics in rivers is of great importance for various practical purposes. Despite its high relevance in riverine environment processes, the monitoring of sediment rates remains a major and challenging task for both suspended and bed load estimation. While the measurement of suspended load is currently an active area of testing with nonintrusive technologies (optical and acoustic), bed load measurement does not mark a similar progress. This paper describes an innovative combination of measurement techniques and analysis protocols that establishes the proof‐of‐concept for a promising technique, labeled herein Acoustic Mapping Velocimetry (AMV). The technique estimates bed load rates in rivers developing bed forms using a nonintrusive measurements approach. The raw information for AMV is collected with acoustic multibeam technology that in turn provides maps of the bathymetry over longitudinal swaths. As long as the acoustic maps can be acquired relatively quickly and the repetition rate for the mapping is commensurate with the movement of the bed forms, successive acoustic maps capture the progression of the bed form movement. Two‐dimensional velocity maps associated with the bed form migration are obtained by implementing algorithms typically used in particle image velocimetry to acoustic maps converted in gray‐level images. Furthermore, use of the obtained acoustic and velocity maps in conjunction with analytical formulations (e.g., Exner equation) enables estimation of multidirectional bed load rates over the whole imaged area. This paper presents a validation study of the AMV technique using a set of laboratory experiments.

An estimation procedure for suspended sediment concentrations based on the intensity of backscattered sound of acoustic Doppler current profilers (ADCP) is introduced in this paper. Based on detailed moving and fixed boat ADCP measurements with concurrent sediment sampling, we have successfully calibrated the estimation method for a reach of River Danube in Hungary, characterized by significant suspended sediment transport. The effect of measurement uncertainty and various data filtering on sediment load determination is also analyzed and quantified. Some of the physical model parameters describing the propagation of sound in water are estimated based on known empirical formulas, while other parameters are derived from measured. Regression analysis is used to obtain a relationship between the intensity of backscattered sound and sediment concentrations. The empirical relationship has been then used to estimate the suspended sediment concentrations from the ADCP data collected in fixed and moving boat measurement operation mode, along verticals and path-lines, respectively. We show that while some measurement uncertainty is inherent to the acoustic Doppler principle, it is further enhanced by the complexity of the near-bottom sediment-laden flow. This uncertainty has then a significant effect on the local sediment load estimation. In turn, reasonable smoothing of raw velocity and backscatter intensity data shows insignificant impact on cross-sectional sediment load estimation.

3D numerical models are increasingly used to simulate flow, sediment transport and morphological changes of rivers. For the simulation of bedload transport, the numerical flow model is generally coupled with an empirical sediment transport model. The application range of the most widely used empirical models is, however, often limited in terms of hydraulic and sedimentological features and therefore the numerical model can hardly be applied to complex situations where different kinds of morphological processes take place at the same time, such as local scouring, bed armoring and aggradation of finer particles. As a possible solution method for this issue, we present the combined application of two bedload transport formulas that widens the application range and thus gives more appropriate simulation results. An example of this technique is presented in the paper by combining two bedload transport formulas. For model validation, the results of a laboratory experiment, where bed armoring, local scouring and local sediment deposition processes occurred, were used. The results showed that the combined application method can improve the reliability of the numerical simulations.

Many pharmaceuticals inevitably end up in surface waters, exerting unwanted biological activity in nontarget organisms. This effect is confined by the compound's environmental persistence. Regulatory laboratory simulation tests are used in persistence assessment and exposure modeling. While doubt has been expressed about the usefulness of laboratory‐derived persistence indicators under field conditions, these remain the only inputs for chemical fate models due to difficulties of measuring persistence in situ, especially at large scales. To improve understanding about relationships between laboratory experiments and the environmental fate in streams, we developed a mathematical model of biodegradation in stream networks and combined it with in‐stream monitoring data to (i) test if persistence could be evaluated from field data, (ii) check if persistence extracted from laboratory tests applied in the field, and (iii) locate hot spots of biodegradation in a large river basin. The model describes partitioning, and particle settling and resuspension, and is structurally compatible with those applied for evaluating laboratory simulation tests. Application to the Rhine river basin suggests that biotransformation rate constants extracted from laboratory tests underestimate those in the field, yet the percentage of biotransformation in the Rhine basin is less than in the laboratory tests due effective biotransformation being limited to small‐ and medium‐sized streams. In conclusion, our data show that biotransformation rates can accurately be predicted if (i) monitoring is performed across a wide range in stream order and (ii) precise estimates for consumption and removal rates at wastewater treatment plants are known.