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Abstract Accurately characterizing the spatiotemporal dynamics of residual and tidal flows is essential for understanding transport processes in tidal rivers and estuaries, as they directly affect salinity intrusion, water renewal capacity, sediment transport, and morphological evolution. This paper aims at characterizing the longitudinal and temporal variability of tidal discharges and currents in the St. Lawrence fluvial estuary (SLFE), under a wide range of river flow and tidal conditions. Tidal discharges and currents are reconstructed by cubature from nonstationary tidal analyses of water levels for a highly variable year, in terms of observed river flows, at 10 river cross-sections of the SLFE, distributed from the fluvial estuary entrance to the head of the tide. An analysis of the spatiotemporal variability in residual and tidal flows is hereby provided, with an emphasis on ebb-flood characteristics, residual currents, tidal constituent properties and tidal wave propagation characteristics at the intratidal, neap-spring and seasonal scales along the system. The main drivers and mechanisms responsible for this variability include (1) the system's hydrology and its associated watershed and meteorological characteristics, which dictate river flow intensity and seasonality, (2) the landward-travelling tides originating from the ocean, responsible for intratidal and tidal monthly variability in tides and currents, (3) nonlinear river-tide interactions, dissipating tidal energy, modulating tidal properties and inducing a surface level gradient, and (4) channel convergence and floodplain morphology, contributing to tidal asymmetry in horizontal and vertical tides. These factors ultimately influence tidal wave propagation and damping properties within estuaries, both longitudinally and at the neap-spring and seasonal scales. Highlights • Tidal discharges and currents are derived from nonstationary tidal analyses of water levels through continuity. • Drivers of flow variability include hydrology, ocean tides, river-tide interactions, and channel and floodplain morphology. • Flood velocities reduce in presence of tidal flats and respond the most strongly to changes in river flow during neap tides. • Flow duration asymmetry is temporally lagged with respect to tidal duration asymmetry due to neap-spring storage effects. • Fortnightly variations in tidal damping are driven by changes in friction closely linked to the neap-spring reversal of LW. [ABSTRACT FROM AUTHOR]

One of the main obstacles to the socio-economic development of the Brazilian Amazon is the lack of electric energy in the numerous small isolated communities of the region that hampers value-added agricultural production, revenue growth and creation of jobs. One way to solve this problem is by setting up micro-hydro power (MHP) plants under a sustainable development perspective. This paper presents a decision support system (DSS) that analyzes this solution. The system considers the hydrological, topographical, geotechnical, environmental, energy, economic and social aspects of the target site. A detailed analysis is made of the hydrological model that employs a rainfall run-off model for small catchment analysis; the energy planning favors a two-turbine method to determine the maximum energy production during demand peaks, and the economic aspects show that the costs of energy generated by MHP plants are comparable to those from rural grid systems and lower than those from from diesel generators. Thus, the use of the hydro-power resources of the small catchments of Amazonia combined with the minimization of the environmental impacts caused by MHP not only fulfills the energy demand of the small communities of region, but is also viable economically along with job creation and revenue generation, and it supports the perspective of sustainable development. [Copyright &y& Elsevier]

Lake Saint-Francois is a fluvial lake of the St. Lawrence system which is used for hydropower production and commercial navigation. For 150 years, it was dredged and dammed regularly without any impact analysis being made. The cumulative impact of dredging and damming on large rivers such as the St. Lawrence is an issue with only qualitative answers. Bidimensional hydrodynamics was used to simulate ancient flow conditions and to produce quantitative descriptors. Two Numerical Field Models (NFM) were prepared, one representing present state geometry, which contains 300,000 sounding points, and the other representing pristine state, based on 1900 and 1870 measurements and containing70,000 soundings. These two NFMs were compared, showing important changes in the morphology of the lake. The NFMs were then used for bidimensional hydrodynamic simulations of both actual and pristine statesfor 3 different discharges: 5,000 m3/s, 7,500 m3/s, and 10,000 m3/s.Results highlight the cumulative physical transformation of the system. Hydrodynamic simulations and velocity differences show an increase of velocities over shoals for discharge under 8,800 m3/s, and a decrease of velocities in deeper water for the same range of discharge. Dredging and straightening around Cornwall Island resulted in changesfrom 64% to 71% of the total river flow passing through the south channel while the flow in the north channel decreased from 36% to 29%. These hydrodynamic transformations had a definitive impact on sedimentation and most probably on aquatic plant distribution. [ABSTRACT FROM AUTHOR]

Maximizing the performance of hydropower plants by taking advantage of the remaining energy downstream of dams via the installation of hydrokinetic turbines is feasible. In these cases, the design of the rotor diameter and velocity are fundamental and depend on the depth and velocity of the river, respectively. In this study, the Saint-Venant model was applied and calibrated by linear regression of measured and simulated flow rates, which resulted in a correlation of 0.99. The validation was performed using measured velocities that are comparable to the simulated velocities. A power curve was generated for the measured flow rates and simulated velocities and obtained a correlation of 0.96. The curve was used to estimate the velocity, calculate the energy density, and define a design velocity of 2.35 m/s. Ten points in the study area were selected for the turbine locations, and the velocities were determined using the power curve for the measured flow rates and simulated velocities. The rotor design was performed using the blade element method (BEM), and a rotor diameter of 10 m was defined. The 10 turbines can generate 2.04 GWh/year of electricity. The results demonstrate the potential for utilising the remaining energy of hydroelectric plants. [ABSTRACT FROM AUTHOR]