Krvavica, N.; Travaš, V., and Ožanić, N., 2017. Salt-wedge response to variable river flow and sea-level rise in the microtidal Rječina River Estuary, Croatia. A finite-volume model for two-layer shallow-water flow is presented and applied to study the dynamic response of a salt wedge in a microtidal estuary to changes in river flow rate and sea-level rise (SLR). First, the shape of the arrested salt wedge was computed for different hydrographic conditions. Next, the response of the salt wedge to highly variable river flow was investigated. Finally, this model was applied to predict the impacts of the SLR on salinity intrusions in the Rječina River Estuary. To assess the model performance and to examine the salinity structure in the estuary, a field-sampling campaign was conducted during 2014 and 2015. Field observations revealed negligible longitudinal density variations in both freshwater and saltwater layers and highly stratified conditions for all considered river flow rates and sea levels. F...

A finite volume model for two-layer shallow water flow in microtidal salt-wedge estuaries is presented in this work. The governing equations are a coupled system of shallow water equations with source terms accounting for irregular channel geometry and shear stress at the bed and interface between the layers. To solve this system we applied the Q-scheme of Roe with suitable treatment of source terms, coupling terms, and wet-dry fronts. The proposed numerical model is explicit in time, shock-capturing and it satisfies the extended conservation property for water at rest. The model was validated by comparing the steady-state solutions against a known arrested salt-wedge model and by comparing both steady-state and time-dependant solutions against field observations in Rječina Estuary in Croatia. When the interfacial friction factor λ_i was chosen correctly, the agreement between numerical results and field observations was satisfactory.

Microplastics (MPs) are found to be omnipresent in marine environments and their production and disposal are constantly increasing. In order to control and mitigate their negative effects on the environment, it is important to understand the processes involved in their transport and sinking. Most of the conducted experimental studies on MP in water have focused on exploring the settling behavior of MP particles under static flow conditions. This paper presents the results of an experimental study of MP particles in a horizontal stream of water. A series of laboratory experiments were carried out to measure the drag coefficient of quasi-radially-symmetric MP particles with different shapes (spheres, cubes, and crosses) and sizes (1.5 to 3.0 mm). In the study, the relationship between the drag coefficient and flow conditions represented by the local Reynolds number is investigated. The experimental procedure was validated, and a total of 400 measurements were performed. Values of the measured drag coefficient ranged from 0.8 to 2.5 for the values of Re from 40 to 300. The results show that the shape of MP particles in the water stream considerably influences the particle drag coefficient, with a rather complex relationship between the drag coefficient and flow conditions.

Leakages in water supply networks can be minimized through pressure reduction or by repairing the resulting damage. The effective implementation of the latter approach necessitates the localization of leaks, for which various methods exist. This paper presents a specific software and hardware configuration for constructing a digital twin of pressurized piping systems that can be utilized for this purpose. The proposed method can identify both the flow and position of leaks and is based on solving an equivalent optimization problem, where the objective function depends on the difference between the measured pressure values at specific points and those predicted at the same points under the same boundary conditions by a computational model. Given the multimodality of the formulated problem, particle swarm optimization is implemented for this task. To enable real-time localization, the measured pressure values are transmitted to a microcontroller, which processes the data and sends it to a Python script. This script employs a while loop to continuously monitor the criteria for leak detection, and when these criteria are met, it initiates a procedure for leak localization. The theoretical aspect of the procedure, as well as its practical implementation, is presented below as an example.