Thermal discharge from power plants causes significant concerns in aquatic environments. The purpose of this study is to evaluate how river mouth morphodynamics, particularly spit development and removal, influence the dispersion of thermal plumes. To achieve this, a case study was carried out at a coastal power plant in southwest Türkiye, where thermal effluent is conveyed to the sea through a low-flow river. Field measurements combined with numerical modeling were used to analyze plume dynamics under varying spit configurations. Results revealed that the evolution of a spit on one side of the river mouth influences plume dispersion and redirects the mixing zone toward the opposite shoreline. Numerical simulations demonstrated that spit development reduces dispersion efficiency (by over 75%), while the physical removal of the spit significantly improves it, reducing temperature excess from 4–5 °C to 0–1 °C within the mixing zone, meeting safe environmental standards. The findings highlight the pivotal role of morphological changes in governing thermal discharge behavior and emphasize the importance of continuous monitoring and management strategies, such as periodic dredging, to ensure compliance with environmental regulations.

Midchannel islands (MCIs) are instream geomorphic units generally emerge in lowland rivers. Despite their significant ecomorphological services in the river ecosystem, the flow patterns around these self-forming riparian landforms and their impacts on aquatic life are not fully understood yet. Understanding the flow pattern around these formations enables practitioners to produce cost-effective, sustainable, and eco-friendly river management projects and strategies, forming the motivation of this study. Herein, the secondary flow pattern around MCIs was analyzed by employing a RANS-based numerical model. Flow around the simplified bodies was simulated to give a more precise analysis regarding flow-island interactions. Once the numerical validation process was completed for the cylinder using an experimental dataset, the validated model was implemented for islands (streamlined island, vertically sloped island (VSI), and realistically sloped island (RSI)). Analysis of the model results revealed the following key findings: 1) the RSI acted like a streamlined object and produced weaker lee-wake vortices with a longer recovery distance compared to the streamlined island and the VSI, 2) the RSI gained a better-streamlined form near the bed than near the water surface due to enhanced elongation, 3) this situation in the RSI case generated highly variable flow patterns along the depth behind the MCI, and 4) due to the three-dimensional geometry of the RSI, the generated large-scale vortices propagated asymmetrically towards the sides of the channel rather than remaining around the centerline.

Midchannel islands were conventionally considered undesirable additional hydraulic resistance to flow for many years and tended to be removed from the main channel as a measure against the flood. Today, it is known that these geomorphic units provide key eco-geomorphological services in the active corridor of natural waterways. This study examined the dynamics behind the occurrence mechanism of midchannel islands considering basin-scale (i.e., land use, elevation, main channel slope, form factor, relief) and fluvial (i.e., sediment yield) variables. Nine drainage basins were selected as samples from the different ecoregions on Earth. Morphometric and hydrological characteristics were determined using hydrological datasets and satellite-based images by means of ArcGIS. Sediment delivery magnitudes for each examined basin were calculated based on an empirical expression. In addition, the development process of isolated midchannel islands was investigated by quantifying their planform morphometric features. The basin-scale analysis showed that the main channel slope, i.e., gravity-induced factors, controls the emergence location of MCIs to a great extent, and the basin sediment yield impacts the density (i.e., number of islands) of MCIs in a unit length of the river. Furthermore, at the individual scale, the morphometric analysis of MCIs revealed that during the MCI growth, the streamlining process diminishes the skin friction. This effect becomes more prominent, particularly at the mature stage of MCIs, and the form drag prevails over the skin friction.

Midchannel islands (MCIs) are influential instream geomorphic units generally emerge in lowland rivers. Despite their significant ecomorphological services in the river ecosystem, the flow structures around these self-forming riparian landforms are not fully understood yet. Understanding the flow pattern around these formations enables practitioners to produce cost-effective, sustainable, and eco-friendly river management projects/strategies. From this motivation, the secondary flow pattern around MCIs was analyzed employing RANS based numerical model. Flow around the simplified bodies were simulated to give a more precise analysis regarding flow-island interactions. Once the numerical validation process was completed for the cylinder using an experimental dataset, the validated model was implemented for islands (streamlined island, vertically sloped island (VSI), and realistically sloped island (RSI)). The simulations revealed these findings: 1) The RSI acted like a streamlined object and produced weaker lee-wake vortices with a longer recovery distance. 2) The RSI gained a better streamlined form near the bed than near the water surface due to enhanced elongation. 3) This situation generated highly variable coherent flow structures along the depth behind the MCI. 4) Due to the three-dimensionality of the RSI, the generated large-scale vortices propagated asymmetrically towards sides of the channel rather than remaining around the centerline.

Flume experiments were conducted to investigate how upward vegetation growth and streamwise patch expansion separately and jointly affect flow around submerged vegetation under depth‑limited conditions. Their individual effects were isolated by increasing canopy height or streamwise patch length while keeping the other parameter constant. The measurements were performed in two different flumes under closely comparable Reynolds‑number conditions. Acoustic Doppler Velocimetry (ADV) characterized velocity and turbulence on the stoss and lee sides of the patch. Non‑intrusive Particle Image Velocimetry (PIV) resolved the mean flow, canopy‑top shear layer, and vorticity above the vegetation, where shallow flow depth made ADV measurements impractical because of possible probe disturbance. Upward vegetation growth produced a stronger velocity deficit and extended the low‑velocity region over a larger part of the water column. It also strengthened the canopy‑top shear layer and increased Reynolds shear stress, turbulent kinetic energy, and vorticity near the canopy interface and within the downstream wake. In contrast, increasing patch length allowed vegetation resistance, vertical momentum exchange, and turbulent mixing to act over a longer distance before the flow reached the patch exit. Consequently, lee‑side Reynolds shear stress and turbulent kinetic energy variations became smoother and less localized. In summary, vegetation height mainly controlled the magnitude and vertical extent of the hydrodynamic response, whereas patch length controlled its streamwise development and the abruptness of adjustment at the patch exit. These complementary effects should be considered when evaluating restored seagrass meadows and nature‑based coastal protection systems.