Debris-flow modeling is a great challenge due to its complex physical mechanism that remains poorly understood. The present research incorporates the effect of rheological features of the non-Newtonian fluid into the complete quasi-single-phase mixture model, which explicitly accommodates the interactions between flow, non-uniform sediment transport, and bed evolution. The effect of rheological features is estimated by Hersch–Bulkley–Papanastasiou model that can be simplified to Bingham or Newtonian models with specific coefficients. The governing equations are solved by a fully conservative numerical algorithm, using an explicit finite volume discretization with well-balanced slope-limited centered scheme combined with an implicit discretization method. One set of large-scaled U.S. Geological Survey debris-flow experiments is applied to investigate the influence of the non-Newtonian fluid on debris-flow modeling. It is found that the present model closed by Hersch–Bulkley–Papanastasiou model performs better than the models without considering effect of rheological features, which may facilitate the development of quasi-single-phase mixture modeling for debris flows.

Purpose: The purpose of this paper is to present a fully conservative numerical algorithm for solving the coupled shallow water hydro-sediment-morphodynamic equations governing fluvial processes, and also to clarify the performance of a conventional algorithm, which redistributes the variable water-sediment mixture density to the source terms of the governing equations and accordingly the hyperbolic operator is rendered similar to that of the conventional shallow water equations for clear water flows.Design/methodology/approach: The coupled shallow water hydro-sediment-morphodynamic equations governing fluvial processes are arranged in full conservation form, and solved by a well-balanced weighted surface depth-gradient method along with a slope-limited centred scheme. The present algorithm is verified for a spectrum of test cases, which involve complex flows with shock waves and sediment transport processes with contact discontinuities over irregular topographies. The computational results of the conventional algorithm are compared with those of the present algorithm and evaluated by available referenced data.Findings: The fully conservative numerical algorithm performs satisfactorily over the spectrum of test cases, and the conventional algorithm is confirmed to work similarly well.Originality/value: A fully conservative numerical algorithm, without redistributing the water-sediment mixture density, is proposed for solving the coupled shallow water hydro-sediment-morphodynamic equations. It is clarified that the conventional algorithm, involving redistribution of the water-sediment mixture density, performs similarly well. Both algorithms are equally applicable to problems encountered in computational river modelling.

During the cofferdam construction of the toe reinforcement project at the Qiantang River Estuary, the scouring of the riverbed at the groin head often led to the collapse of geotube groins due to strong tidal currents. Based on field experience, employing a combination of clay and geotubes proved to be a more effective solution to this problem. This study adopted a flume model experiment to investigate the scouring and deposition around geotube groins and mixed clay–geotube groins. The results indicated that the influence of tidal surges on geomorphic changes surrounding the groins was more pronounced during spring tides than during neap tides. Under the same flow conditions, the scour depth at the head of the geotube groin was notably deeper than that of the mixed clay–geotube groin. Additionally, sediment silting behind the mixed clay–geotube groin was significantly greater than that behind the geotube groin. The clay component of the mixed clay–geotube groin served to mitigate the head scour, enhancing the overall structural stability to a certain extent. The geotube groin, with its surrounding scour pits expanding over time, experienced increasing tensile strain. This resulted in the rupture of the geotextile material, the loss of internal sand and, ultimately, groin collapse. It was found that mixed clay–geotube groins were better suited for cofferdam construction in strong tidal estuaries compared to geotube groin alternatives.

The development of renewable energy is an effective avenue for achieving net zero goals. It requires many energy storage systems (ESSs) for adjusting the unstable power generated by renewable energy. To date, PSH is the most technically mature, economically reasonable, and reliable ESS. Currently, various countries have developed PSH. As of 2022, the global installed capacity of PSH has reached 175,060 MW, with an annual increase of 10,300 MW. This paper addresses several technical considerations in the preliminary design of PSH systems, drawing on extensive design experience. Key factors such as the selection of dam sites, installed capacity, and characteristic water levels are thoroughly discussed. These design choices are influenced by a range of factors, including geological and topographical conditions, hydrological parameters, environmental impacts, sedimentation, submersion areas, and resettlement issues. PSH is highly effective in meeting power demands, regulating frequency and phase, serving as an emergency power reserve, and improving the power factor of electrical networks. It enhances the quality of renewable energy sources such as wind, photovoltaic, and tidal power, which are characterized by intermittent supply. Beyond its technical advantages, PSH also contributes to local employment and tourism and supports pollutant reduction efforts. Compared to other energy storage systems, PSH has a more significant environmental impact and requires a longer construction period. Thus, exploring new forms of PSH is crucial. Innovative approaches such as utilizing constructed reservoirs, lakes, seas, and abandoned pits can reduce both investment and construction time while minimizing the environmental impact. This paper aims to provide some technical references and feasible plans to governments, owners, and engineers during the planning and preliminary design stages of a PSH project.