[1] Analytical solutions of the one-dimensional hydrodynamic equations for tidal wave propagation are now available and, in this paper, presented in explicit equations. For given topography, friction, and tidal amplitude at the downstream boundary, the velocity amplitude, the wave celerity, the tidal damping, and the phase lag can be computed. The solution is based on the full nonlinearized St. Venant equations applied to an exponentially converging channel, which may have a bottom slope. Two families of solutions exist. The first family consists of mixed tidal waves, which have a phase lag between zero and p/2, which occur in alluvial coastal plain estuaries with almost no bottom slope; the second family consists of ''apparent standing'' waves, which develop in short estuaries with a steep topography. Asymptotic solutions are presented for progressive waves, frictionless waves, waves in channels with constant cross section, and waves in ideal estuaries where there is no damping or amplification. The analytical method is accurate in the downstream, marine part of estuaries and particularly useful in combination with ecological or salt intrusion models. The solutions are compared with observations in the Schelde, Elbe, and Mekong estuaries.

[1] This paper explores different analytical solutions of the tidal hydraulic equations in convergent estuaries. Linear and quasi-nonlinear models are compared for given geometry, friction, and tidal amplitude at the seaward boundary, proposing a common theoretical framework and showing that the main difference between the examined models lies in the treatment of the friction term. A general solution procedure is proposed for the set of governing analytical equations expressed in dimensionless form, and a new analytical expression for the tidal damping is derived as a weighted average of two solutions, characterized by the usual linearized formulation and the quasi-nonlinear Lagrangean treatment of the friction term. The different analytical solutions are tested against fully nonlinear numerical results for a wide range of parameters, and compared with observations in the Scheldt estuary. Overall, the new method compares best with the numerical solution and field data. The new accurate relationship for the tidal damping is then exploited for a classification of estuaries based on the distance of the tidally averaged depth from the ideal depth (relative to vanishing amplification) and the critical depth (condition for maximum amplification). Finally, the new model is used to investigate the effect of depth variations on the tidal dynamics in 23 real estuaries, highlighting the usefulness of the analytical method to assess the influence of human interventions (e.g. by dredging) and global sea-level rise on the estuarine environment.Citation: Cai, H., H. H. G. Savenije, and M. Toffolon (2012), A new analytical framework for assessing the effect of sea-level rise and dredging on tidal damping in estuaries,

Water temperature controls many biochemical and ecological processes in rivers, and theoretically depends on multiple factors. Here we formulate a model to predict daily averaged river water temperature as a function of air temperature and discharge, with the latter variable being more relevant in some specific cases (e.g., snowmelt-fed rivers, rivers impacted by hydropower production). The model uses a hybrid formulation characterized by a physically based structure associated with a stochastic calibration of the parameters. The interpretation of the parameter values allows for better understanding of river thermal dynamics and the identification of the most relevant factors affecting it. The satisfactory agreement of different versions of the model with measurements in three different rivers (root mean square error smaller than 1 o C, at a daily timescale) suggests that the proposed model can represent a useful tool to synthetically describe medium-and long-term behavior, and capture the changes induced by varying external conditions.

The role of riparian vegetation in shaping river morphology is widely recognized. The interaction between vegetation growth and riverbed evolution is characterized by complex nonlinear feedbacks, which hinder direct estimates of the role of key elements on the morphological evolutionary trajectories of gravel bed rivers. Adopting a simple theoretical framework, we develop a numerical model which couples hydromorphodynamics with biomass dynamics. We perform a sensitivity analysis considering several parameters as flood intensity, type of vegetation, and groundwater level. We find that the inclusion of vegetation determines a threshold behavior, identifying two possible equilibrium configurations: unvegetated versus vegetated bars. Stable vegetation patterns can establish only under specific conditions, which depend on the different environmental and species-related characteristics. From a management point of view, model results show that relatively small changes in water availability or species composition may determine a sudden shift between dynamic unvegetated conditions to more stable, vegetated rivers.

The present study provides a detailed quantification of the 'thermopeaking' phenomenon, which consists of sharp intermittent alterations of stream thermal regime associated with hydropeaking releases from hydroelectricity plants. The study refers to the Noce River (Northern Italy), a typical hydropower-regulated Alpine stream, where water stored in high-altitude reservoirs often has a different temperature compared with the receiving bodies. The analysis is based on a river water temperature dataset that has been continuously collected for 1 year at 30-min intervals in four different sections along the Noce River. A suitable threshold-based procedure is developed to quantify the main characteristics of thermopeaking, which is responsible for thermal alterations at different scales. The application of Wavelet Transform allows to separately investigate the thermal regime alterations at sub-daily, daily and weekly scales. Moreover, at a seasonal scale, patterns of 'warm' and 'cold' thermopeaking can be clearly detected and quantified. The study highlights the relevance of investigating a variety of short-term alterations at multiple time scales for a better quantitative understanding of the complexity that characterizes the river thermal regime. The outcomes of the analysis raise important interdisciplinary research questions concerning the effects of thermopeaking and of the related short-and medium-term effects on biological communities, which have been rather poorly investigated in ecological studies.

Temperature of the surface layer of temperate lakes is reconstructed by means of a simplified model on the basis of air temperature alone. The comparison between calculated and observed data shows a remarkable agreement (Nash-Sutcliffe efficiency indices always larger than 0.87, mean absolute errors of approximately 1uC) for all 14 lakes investigated (Mara, Sparkling, Superior, Michigan, Huron, Erie, Ontario, Biel, Zurich, Constance, Garda, Neusiedl, Balaton, and Baikal, in west-to-east order), which present a wide range of morphological and hydrological characteristics. Differently from a pure heat flux balance approach, where the different fluxes are determined on the basis of independent relationships, the input data directly inform parameters of a simple model that, in turn, provides meaningful information about the properties of the real system. The dependence of the model parameters on the main morphological indicators is presented, which allows for a quantitative description of the strong influence of the mean depth of the lake on the thermal inertia and the hysteresis pattern between air and lake surface temperatures.The temperature of the surface layer is a crucial factor for the hydrodynamics and ecology of lakes. Water temperature changes may have important direct and indirect ecological effects via their influence on the lifehistory processes of organisms (metabolism, growth, reproduction) and the properties of the habitats (Winder and Sommer 2012). Temperature variations affect foodweb structures and the availability of nutrients for the biological systems in a lake. The effects of temperature on physical and chemical characteristics of lakes may also modify the distribution of individual taxa from the microbiological to the top predator scale (Eggermont and Heiri 2012;Wojtal-Frankiewicz 2012;De Senerpont Domis et al. 2013).Surface temperature is the result of heat fluxes at the lake surface (short-wave solar radiation, long-wave radiation from and to the lake, sensible and latent heat exchange) and at the boundaries (inflows and outflows, groundwater exchange, precipitation, etc.), and of heat transport due to mixing within the lake. All these fluxes depend on several variables (solar radiation, air temperature, wind speed and direction, cloudiness, relative humidity, etc.), some of which may be difficult or expensive to measure reliably and with sufficient precision. Moreover, some of the variables can change significantly over the lake surface and in time (e.g., wind), and reconstructing their spatial variation can be a particularly hard task. Predicting water temperature is nonetheless a desired goal and models of different types and of different complexity have been proposed, ranging from simple regression models (Livingstone and Lotter 1998;Sharma et al. 2008) to more complex process-based numerical one-dimensional Perroud et al. 2009;Thiery et al. 2014) and three-dimensional models (Wahl and Peeters 2014).In this work, we aim at obtaining results that are accurate enough to reliably p...

[1] In this paper we extend the validity of the classical linear solution for tidal hydrodynamics including the effects of width and depth convergence. Reworking such a solution in the light of externally defined, dimensionless parameters we are able to provide simple relationships to predict the most relevant features of the tidal wave at the estuary mouth (velocity amplitude, phase lag, wavelength, and damping) and to reproduce the main dynamics of tidal wave propagation along finite and infinite length channels. We also highlight the need for an accurate treatment of the linearized bed shear stress by exploiting an iterative procedure, and we show the improvement that can be reached by subdividing the entire estuary in shorter reaches. Different versions of the analytical solution are compared with numerical results, highlighting the strengths and weaknesses of the linear model.

During the last several decades, the Great Lakes region has been experiencing a significant rise in temperatures, with the extraordinary summer warming that affected Lake Superior in 1998 as an example of the marked response of the lake to increasingly warmer atmospheric conditions. In this work, we combine the analysis of this exceptional event with some synthetic scenarios, to achieve a deeper understanding of the main processes driving the thermal dynamics of surface water temperature in Lake Superior. The analysis is performed by means of the lumped model air2water, which simulates lake surface temperature as a function of air temperature alone. The model provides information about the seasonal stratification dynamics, suggesting that unusual warming events can result from two factors: anomalously high summer air temperatures, and increased strength of stratification resulting from a warm spring. The relative contribution of the two factors is quantified using the model by means of synthetic scenarios, which provide a simple but effective description of the positive feedback between the thermal behavior and the stratification dynamics of the lake.