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With global warming and the increase in extreme precipitation events, floods are becoming more frequent in mountainous areas, and the safety of lives and property of people is seriously threatened. However, understanding of the flooding process in uninformative mountainous areas is limited due to the lack of high-quality hydrometeorological data. Hence, this study adopts the MIKE21 model to simulate flood inundation in the Shadai River basin in the Qilian Mountain region of the northern Tibetan Plateau as an example. This validates the modelsimulated flow and inundation extent using the flow data obtained from the calculation of the flood trace points, extent of inundation, and high-resolution remote sensing images. The results show that the flash flood inundation mainly occurs at 12:00-01:00 AM on 18 August 2022, and the simulated and actual maximum inundation areas are 7.9 and 9.5 km², respectively. The fitted F-statistic value is 0.81, and the relative error between the calculated flow rate of the flood trace point and the model-simulated flow rate is 8%, indicating good consistency. Furthermore, an in-depth exploration of the model parameter sensitivity reveals that the use of distributed Manning's roughness coefficient value has higher simulation accuracy. [ABSTRACT FROM AUTHOR]

In order to improve the water quality and the ability to prevent the risk of water environment pollution in the tidal reach of Xiaoqing River, numerical simulation of water quality was carried out in tidal reach of Xiaoqing River. The MIKE21 was used to build a hydrodynamic- water quality coupling model. The main exceeding pollutants COD, TN and TP were selected, and the model was calibrated and verified by the measured water quality data. The water quality changes of the tidal reach under three scenarios of different upstream water quality, differ- ent pollution reduction conditions and sudden water pollution in different water periods were simulated. The results show that the calibrated and validated hydrodynamic-water quality coupling model is well suitable for the tidal reach of Xiaoqing River. When the upstream water is class IV, COD and TP are basically achieved, and TN exceeds the standard. When the upstream water is class V, none of the indicators are up to standard. The upstream water quality should be controlled within the range of class IV as much as possible, and the TN pollution control of the basin water body should be strengthened. Reducing 30% of point and non-point source pollution can effectively reduce COD and TP pollution, but the improvement effect on TN is not good. The influence of polluted water on water body lastes longer and the concentration is higher in the migration process of normal periods. In the wet period, the migration speed will be faster and the emergency treatment time will be less. [ABSTRACT FROM AUTHOR]

In the face of depleting fossil energy and the imperative of sustainable development, there is a compelling drive towards advancing renewable energies. In this context, sustainable and predictable alternatives, like marine energy, gain prominence. Marine energy presents a cleaner option devoid of the adverse effects associated with fossil fuels, playing a crucial role in environmental sustainability by safeguarding coastlines against erosion. This study focuses on Astara Port in the Caspian Sea, exploring the utilization of wave energy converters (WECs). The originality of this study's research lies in exploring WECs' dual role in energy generation and coastal protection. Using MIKE21 software simulations, the impact of number, location, arrangement, and orientation of WECs across various scenarios was investigated, including two WEC number scenarios (11 and 13), three structural placement scenarios (north, front, and south of the port), two structural arrangement scenarios (linear and staggered), two port layout scenarios (original layout and modified layout), and two orientation scenarios for the structures (facing north-east, which is the dominant wave direction, and facing southeast). The results show a remarkable decrease in the significant wave height behind WECs, notably with 13 staggered devices facing dominant waves (from northeast), reducing the significant wave height Hs by 23–25%. This setup also shows the highest wave height reduction, notably 36.26% during a storm event. However, linear WEC setup offers more extensive coastline protection, covering 47.88% of the model boundary during storms. Furthermore, the 11 staggered WECs facing southeast (SE) arrangement had the lowest sediment accumulation at 0.0358 m over one year, showing effective sedimentation mitigation potential. Conversely, the 13 linear WECs facing northeast (NE) had the highest accumulation at 0.1231 m. Finally, the proposed port design redirects high-velocity flow away from the port entrance and removes rotatory flow, reducing sediment accumulation near the harbor entrance. [ABSTRACT FROM AUTHOR]

The diffusion of offshore salt in inland rivers along with tidal waves has an important effect on the aquatic ecological environment of the estuary area.This paper,taking the Wanquan River Estuary as an example,used the Mike21 model to simulate the salinity distribution along the channel under different runoff and tidal levels and analyzed the change rules and leading factors.The results show that the river system and riverbed topography at the Wanquan River Estuary reduce the upward diffusion of salt propelled by the tide and that the salt is mainly distributed in the waters near the estuary.The salinity distribution along the upper reaches of the river decreases rapidly,and it basically remains unchanged when the tidal level increases by 0.1 m and 0.3 m,respectively.A sudden increase in salinity occurs where a curved or narrow channel changes the local water flow and salt accumulates.The upward diffusion range of salt is mainly affected by runoff. When the runoff reaches 106 m3/s and 148 m3/s,the tidal level needs to increase by 0.1 m and 0.3 m respectively before it has an impact.Different degrees of change in runoff and tidal level have different effects on salinity distribution at the estuary,and channel conditions play a key role.

• An experimental study and conducted to investigate the sand mining pit modelling. • A two-dimensional meshless depth averaged model was set-up to simulate the experiments. • Numerical and experimental results so that the maximum error was limited to less than 10%. • The results also indicated that for a flood event with a return period of 25 years. • Sand and gravel mining changed the bed profile up to 1.27 m at the bridge foundation. Irregular, unauthorized and non-technical mining of sand and gravel from rivers play an important role in undesirable changes in morphology and environment. The present experimental study investigated sand mining pit modelling in the different scenarios. A two-dimensional flexible mesh, depth averaged model was set-up to simulate the experiments. The results exhibited an acceptable agreement between the numerical and experimental results, so that the maximum error was limited to less than 10%. After verifying the numerical model, a critical reach in Helleh River was selected as a case study. The effect of sand and gravel mining on a bridge at the site was studied. The results also indicated that for a flood event with a return period of 25 years, sand and gravel mining changed the bed profile up to 1.27 m at the bridge foundation. Moreover, initial signs of river meandering emerged in one scenario. [ABSTRACT FROM AUTHOR]