Seasonal behaviour of tidal damping and residual water level slope in the Yangtze River estuary: identifying the critical position and river discharge for maximum tidal damping

As a tide propagates into the estuary, river discharge affects tidal damping, primarily via a friction term, attenuating tidal motion by increasing the quadratic velocity in the numerator, while reducing the effective friction by increasing the water depth in the denominator. For the first time, we demonstrate a third effect of river discharge that may lead to the weakening of the channel convergence (i.e. landward reduction of channel width and/or depth). In this study, monthly averaged tidal water levels (2003–2014) at six gauging stations along the Yangtze River estuary are used to understand the seasonal behaviour of tidal damping and residual water level slope. Observations show that there is a critical value of river discharge, beyond which the tidal damping is reduced with increasing river discharge. This phenomenon is clearly observed in the upstream part of the Yangtze River estuary (between the Maanshan and Wuhu reaches), which suggests an important cumulative effect of residual water level on tide–river dynamics. To understand the underlying mechanism, an analytical model has been used to quantify the seasonal behaviour of tide–river dynamics and the corresponding residual water level slope under various external forcing conditions. It is shown that a critical position along the estuary.info:eu-repo/semantics/publishedVersio

A data-driven model to quantify the impact of river discharge on tide-river dynamics in the Yangtze River estuary

Understanding the role of river discharge on tide-river dynamics is of essential importance for sustainable water management (flood control, salt intrusion, and navigation) in estuarine environments. It is well known that river discharge impacts fundamental tide-river dynamics, especially in terms of subtidal (residual water levels) and tidal properties (amplitudes and phases for different tidal constituents). However, the quantification of the impact of river discharge on tide-river dynamics is challenging due to the complex interactions of barotropic tides with channel geometry, bottom friction, and river discharge. In this study, we propose a data-driven model to quantify the impact of river discharge on tide-river dynamics, using water level time series data collected through long-term observations along an estuary with substantial variations in river discharge. The proposed model has a physically-based structure representing the tide-river interaction, and can be used to predict water level using river discharge as the sole predictor. The satisfactory correspondence of the model outputs with measurements at six gauging stations along the Yangtze River estuary suggest that the proposed model can serve as a powerful instrument to quantify the impacts of river discharge on tide-river dynamics (including time-varying tidal properties and tidal distortion), and separate the contribution made by riverine and tidal forcing on water level. The proposed approach is very efficient and can be applied to other estuaries showing considerable impacts of river discharge on tide-river dynamics.info:eu-repo/semantics/publishedVersio

Research on Hydraulics and River Dynamics

This Special Issue includes nine original contributions focused on river hydraulics. Four of these resulted from cooperation between universities from different countries: (a) Russia and Poland , (b) Taiwan and the USA , (c) Iran and Italy, and (d) India and Italy . The other contributions resulted from research carried out in universities from South Korea [5], Greece [6], China , and Japan

Significance of cutoff in meandering river dynamics

The occurrence of cutoff events, although sporadic, is a key component in the complex dynamics of meandering rivers. In the present work, we show that cutoff has a twofold role: (1) It removes older meanders, limiting the planform geometrical complexity (geometrical role), and (2) it generates an intermittent noise that is able to influence the spatiotemporal dynamics of the whole river (dynamical role). The geometrical role limits the spatial evolution of the meanders, sporadically eliminating portions of the river planimetry. In this way it stabilizes the mean river geometry around a statistically steady state. The dynamical role is due to the propagation of a noise wave that is triggered by cutoff events. Because of the spatial memory component which is present in the meandering dynamics, such waves propagate all along the river, thus affecting its meandering dynamic

Tertiary Regulation of Cascaded Run-of-the-River Hydropower in the Islanded Renewable Power System Considering Multi-Timescale Dynamics

To enable power supply in rural areas and to exploit clean energy, fully renewable power systems consisting of cascaded run-of-the-river hydropower and volatile energies such as pv and wind are built around the world. In islanded operation mode, the primary and secondary frequency control, i.e., hydro governors and automatic generation control (AGC), ensure the frequency stability. However, due to limited water storage capacity of run-of-the-river hydropower and river dynamics constraints, without coordination between the cascaded plants, the traditional AGC with fixed participation factors cannot fully exploit the adjustability of cascaded hydropower. When imbalances between the volatile energy and load occur, load shedding can be inevitable. To address this issue, this paper proposes a coordinated tertiary control approach by jointly considering power system dynamics and the river dynamics that couples the cascaded hydropower plants. The timescales of the power system and river dynamics are very different. To unify the multi-timescale dynamics to establish a model predictive controller that coordinates the cascaded plants, the relation between AGC parameters and turbine discharge over a time interval is approximated by a data-based second-order polynomial surrogate model. The cascaded plants are coordinated by optimising AGC participation factors in a receding-horizon manner, and load shedding is minimised. Simulation of a real-life system shows a significant improvement in the proposed method in terms of reducing load shedding.Comment: Submitted to IET Renewable Power Generation; 11 page

Convective nature of planimetric instability in meandering river dynamics

The convective nature of the linear instability of meandering river dynamics is analytically demonstrated and the corresponding Green's function is derived. The wave packet due to impulsive disturbance migrates along a river either downstream or upstream, depending on the subresonant or superresonant conditions. The influence of the parameters that govern the meandering process is shown and the role of the fluid dynamic detail used to describe the morphodynamic problem is discussed. A numerical simulation of the river planimetry is also develope

River Dynamics Forecasting using TELEMAC, Earth Observation and AI

Hydrodynamic

Meandering river dynamics

Meandering channels are dynamic landforms that arise as a result of fluid mechanic and sedimentary processes. Their evolution has been described by the meander morphodynamic equations, which dictate that channel curvature and bed topology give rise to local perturbations in streamwise fluid velocity, prompting the preferential erosion and sediment deposition that constitute meander behavior. Previous theoretical work has been based on simplified periodic systems. Here we determine the mathematical conditions required for unique solutions to the meander morphodynamics equations. Our predictions for non-periodic finite-domains constitute the first correct explanation of behavior observed in flumes, where a fixed inlet leads to the long-term decay of all meanders. We show that a continuous perturbation is required for sustained meandering. With a driven perturbation at the inlet, we find that high (low) frequency driving results in spatial decay (growth). We present original scaling arguments for the dependence of the meander migration rate on geological parameters, showing that the rate of migration increases with increased width, down-reach slope, and bank erodibility, and decreases with increased volumetric flow rate. The meander equations involve a single dimensionless parameter alpha, which characterizes the ratio of secondary to irrotational flow. We show that variations in alpha have significant impact on spatial and temporal scaling, and on the degree of upstream skewing in meander shapes. For numerical simulations, we develop a rigorous mathematical description of the relationship between spatial discretization schemes and numerical stability, and we present a robust, stable numerical algorithm. We introduce a parametric Lagrangian variable for improved stability and adaptive spatial resolution. Our implicit numerical solver facilitates a time-step size which is limited by accuracy instead of stability, leading to a significant improvement in computational speed. We present the first demonstrably accurate, converged solutions for the meander morphodynamics equations. Our nonlinear work has focused on the evolution of initially quiescent systems with boundary driving. We find that finite-domain theory accurately describes behavior close to the upstream boundary, whereas standard period-domain behavior dominates downstream. In the instance of clamped upstream boundaries, nonlinear simulation leads to a significantly longer progression of the initial disturbance relative to linear theory before subsiding into a straight channel. We find that upstream perturbations will cause the excitation of temporally growing waves downstream. Finally, we provide rigorous scaling analysis to determine the appropriate length of experimental flumes, the appropriate duration of experimental runs, and the necessary properties of sediment. We present simulations of previous experimental work and find good heuristic agreement, and we provide recommendations for experimental conditions for the observation of sustained meandering in laboratory flumes

Rusne-Šilute Road Impact on Nemunas River Dynamics near Rusne

River, Estuarine and Coastal Dynamic

What next? Rewilding as a radical future for the British countryside

Rewilding is an optimistic environmental agenda to reverse the loss of biodiversity and reconnect society with nature. This chapter explores Britain’s ecological history, back to the Last Interglacial before the arrival of modern humans, when the climate was similar to today, to analyse how conservationists can learn from the past to rewild the ecosystems of the present and prepare for an uncertain future. Because there is no single point in history that should or could be recreated, rewilding focuses on re-establishing naturally dynamic ecological processes that, through an appropriate sequence of species reintroductions, attempts to move the ecosystem towards a more appropriately biodiverse and functional state. A state that is self-sustaining in the present climate, and that projected for the near future. Specifically, this chapter explores a rewilding solution to conservation challenges associated with over-grazing, limited germination niche availability, and river dynamics: the reintroduction of wolves, wild boar, and beaver respectively. This sequence of reintroductions is suggested to be complimentary, each altering ecosystem dynamics to facilitate the return of the next. Evidence indicates wolves will reduce deer abundance and re-distribute browsing intensity promoting tree regeneration, particularly in riparian areas, increasing woodland availability to the more habitat-dependent wild boar and beaver. An important message behind rewilding is that a rich biodiversity with all guilds well represented, including the ones that polarize public opinion, such as large predators, are important components of ecosystem service rich and self-sustaining ecosystems, particularly in core areas