Publications

The fate of Lake Baikal: how climate change may alter deep ventilation in the largest lake on Earth 2018

Piccolroaz, Sebastiano; Toffolon, Marco, "The fate of Lake Baikal: how climate change may alter deep ventilation in the largest lake on Earth" in CLIMATIC CHANGE, v. 150, n. 3-4 (2018), p. 181-194. - URL: https://link.springer.com/article/10.1007/s10584-018-2275-2 . - DOI: 10.1007/s10584-018-2275-2

2018 journal paper

Exploring and quantifying river thermal response to heatwaves 2018

Piccolroaz, Sebastiano; Toffolon, Marco; Robinson, Christopher T.; Siviglia, Annunziato, "Exploring and quantifying river thermal response to heatwaves" in WATER, v. 10, n. 8 (2018), p. 1098. - URL: http://www.mdpi.com/2073-4441/10/8/1098/pdf . - DOI: 10.3390/w10081098

2018 journal paper

Thermal discontinuities along a lowland river: The importance of urban areas and lakes 2018

Arora, Roshni; Toffolon, Marco; Tockner, Klement; Venohr, Markus, "Thermal discontinuities along a lowland river: The importance of urban areas and lakes" in JOURNAL OF HYDROLOGY, v. 564, (2018), p. 811-823. - URL: www.elsevier.com/inca/publications/store/5/0/3/3/4/3 . - DOI: 10.1016/j.jhydrol.2018.05.066

Despite increasing knowledge on the spatio-temporal dynamics of river temperature, a master water quality variable, it remains a challenge to identify the landscape variables influencing thermal heterogeneity along entire river courses. The present study investigated the spatial heterogeneity of stream temperature (ST), and the role of landscape variables, at 20 locations along the 195 km course of the intensively managed lowland River Spree (NE Germany) over a period of nine months. Along the river, four distinct thermal sections were identified, created by thermal discontinuities induced by lakes and an urban area. Three approaches, namely heat budget modelling (estimating the unresolved residual heat flux), both in Eulerian and Lagrangian form, semi-empirical air2stream modelling, and statistical correlations were applied to quantify the observed thermal heterogeneity and the role of climatic (air temperature) and landscape variables (land use, lakes, stream azimuth). Urban areas and lakes were identified as heat sources (in summer), which induced ST discontinuities at different time scales (daily, monthly and during the entire study period). Statistical correlations showed that heat inputs and ST increased with increasing urban area and decreased with distance from lakes. Furthermore, comparison of observed STs and those simulated via the Lagrangian model revealed that heat advection was the dominant thermal process in a lake-influenced section and persisted over a distance of up to 20 km. Simulations showed that this effect could not be significantly diminished even by complete riparian shading along the section, as the sub-daily ST reduced by an average of only 1.5 degrees C. Hence, plantation of riparian buffers should be complemented with additional mitigation measures such as improving the groundwater table recharge, managing the temperature of urban discharges, to mitigate climate change impacts on ST.

2018 journal paper

CLIMATE CHANGE PROJECTIONS FOR LAKES SURFACE WATER TEMPERATURE IN THE LAURENTIAN GREAT LAKES REGION: UNCERTAINTY ASSESSMENT 2018

Piccioni, F.; Piccolroaz, S.; Toffolon, M.; Majone, B., "CLIMATE CHANGE PROJECTIONS FOR LAKES SURFACE WATER TEMPERATURE IN THE LAURENTIAN GREAT LAKES REGION: UNCERTAINTY ASSESSMENT" in Book of abstracts ELLS-IAGLR-2018, Evian: INRA, 2018. Proceedings of: ELLS-IAGLR-2018, Evian (France), 23th - 28th September 2018

2018 extended abstract

Wind variability and Earth’s rotation as drivers of transport in a deep, elongated subalpine lake: The case of Lake Garda 2018

Amadori, Marina; Piccolroaz, Sebastiano; Giovannini, Lorenzo; Zardi, Dino; Toffolon, Marco, "Wind variability and Earth’s rotation as drivers of transport in a deep, elongated subalpine lake: The case of Lake Garda" in JOURNAL OF LIMNOLOGY, v. 77, n. 3 (2018), p. 505-521. - URL: https://www.jlimnol.it/index.php/jlimnol/article/view/jlimnol.2018.1814/1473 . - DOI: 10.4081/jlimnol.2018.1814

The effects of wind forcing and Earth's rotation on the transport processes in Lake Garda (Italy) are investigated for the first time under different thermal stratification conditions and typical diurnal wind cycles. Numerical simulations are performed by means of a modeling chain composed of a meteorological (WRF) and a hydrodynamic (Delft3D) model. Transport processes are studied through the combined analysis of the residual (time averaged) flow field and the trajectories of Lagrangian particles. Results show that strong currents develop in winter under the forcing of synoptic northerly Him winds, especially in the elongated northern region, where winds are channeled by the steep orography. Significant water volumes are displaced laterally by Ekman transport, producing intense downwelling and upwelling along the steep shores. Instead summer patterns are controlled by the diurnal cycle of local breezes, alternately blowing along the main axis of the lake. The resulting circulation reveals counterclockwise gyres in the northern part, driven by the alternating wind direction and affected by Coriolis force. The analysis suggests that complex circulations can develop in lakes with relatively simple geometries, like the narrow trunk region of Lake Garda, where the effect of Earth's rotation unexpectedly influences the transport patterns.

2018 journal paper

Eutrophication, research and management history of the shallow Ypacaraí Lake (Paraguay) 2018

Moreira, M. Gregorio Alejandro López; Hinegk, Luigi; Salvadore, Andrea; Zolezzi, Guido; Hölker, Franz; Domecq, S. Roger Arturo Monte; Bocci, Martina; Carrer, Sebastiano; De Nat, Luca; Escribá, Juan; Escribá, Carmen; Benítez, Gilberto Antonio; Ávalos, Claudia Raquel; Peralta, Inocencia; Insaurralde, Mario; Mereles, Fátima; Sekatcheff, Jean Michel; Wehrle, Andrés; Facetti-Masulli, Juan Francisco; Facetti, Juan Francisco; Toffolon, Marco, "Eutrophication, research and management history of the shallow Ypacaraí Lake (Paraguay)" in SUSTAINABILITY, v. 10, n. 7 (2018). - URL: http://www.mdpi.com/2071-1050/10/7/2426/pdf . - DOI: 10.3390/su10072426

Ypacaraí Lake is the most renowned lake in landlocked Paraguay and a major source of drinking and irrigation water for neighbouring towns. Beyond its socioeconomic and cultural significance, it has great ecological importance, supporting a rich biodiversity. Rapid growth of human presence and activities within its basin has led to its environmental degradation, a heartfelt matter of high political concern that compels intervention. Here, by reconstructing the history of scientific and management-oriented research on this system, we provide a comprehensive assessment of current knowledge and practice to which we contribute our recent, novel findings. An upward trend in total phosphorus concentration confirms ongoing eutrophication of an already eutrophic system, evidenced by consistently high values of trophic state indices. Downward trends in water transparency and chlorophyll-a concentration support the hypothesis that primary production in this lake is fundamentally light limited. Statistical and other analyses suggest high sensitivity of the system to hydraulic, hydro-morphological and hydro-meteorological alterations arising, respectively, from engineering interventions, land use and climate change. By discussing knowledge gaps, opportunities for research and challenges for management and restoration, we argue that this case is of high scientific value and that its study can advance theoretical understanding of shallow subtropical lakes.

2018 journal paper

Frictional interactions between tidal constituents in tide-dominated estuaries 2018

Cai, Huayang; Toffolon, Marco; Savenije, Hubert H. G.; Yang, Qingshu; Garel, Erwan, "Frictional interactions between tidal constituents in tide-dominated estuaries" in OCEAN SCIENCE, v. 14, n. 4 (2018), p. 769-782. - URL: http://www.ocean-sci.net/volumes_and_issues.html . - DOI: 10.5194/os-14-769-2018

When different tidal constituents propagate along an estuary, they interact because of the presence of nonlinear terms in the hydrodynamic equations. In particular, due to the quadratic velocity in the friction term, the effective friction experienced by both the predominant and the minor tidal constituents is enhanced. We explore the underlying mechanism with a simple conceptual model by utilizing Chebyshev polynomials, enabling the effect of the velocities of the tidal constituents to be summed in the friction term and, hence, the linearized hydrodynamic equations to be solved analytically in a closed form. An analytical model is adopted for each single tidal constituent with a correction factor to adjust the linearized friction term, accounting for the mutual interactions between the different tidal constituents by means of an iterative procedure. The proposed method is applied to the Guadiana (southern Portugal–Spain border) and Guadalquivir (Spain) estuaries for different tidal constituents (M2, S2, N2, O1, K1) imposed independently at the estuary mouth. The analytical results appear to agree very well with the observed tidal amplitudes and phases of the different tidal constituents. The proposed method could be applicable to other alluvial estuaries with a small tidal amplitude-to-depth ratio and negligible river discharge.

2018 journal paper

On the predictability of lake surface temperature using air temperature in a changing climate: A case study for Lake Tahoe (U.S.A.) 2018

Piccolroaz, Sebastiano; Healey, N. C.; Lenters, J. D.; Schladow, S. G.; Hook, S. J.; Sahoo, G. B.; Toffolon, Marco, "On the predictability of lake surface temperature using air temperature in a changing climate: A case study for Lake Tahoe (U.S.A.)" in LIMNOLOGY AND OCEANOGRAPHY, v. 2018, n. 63.1 (2018), p. 243-261. - URL: https://aslopubs.onlinelibrary.wiley.com/doi/full/10.1002/lno.10626 . - DOI: 10.1002/lno.10626

Can we predict long-term trends of lake surface temperature based on air temperature alone? We explore this question by analyzing the performance of a hybrid model (air2water) as a predictive tool for defining scenarios of lake surface temperature in the framework of climate change studies. Employing Lake Tahoe (U.S.A.) as a case study, we apply the model using different air temperature datasets (in situ measurements, gridded observations, and downscaled General Circulation Models). Through a data-driven calibration of the model parameters based on surface water temperature records, we show that air2water provides good performance (root mean square error ∼ 0.5°C, on a monthly scale) regardless of the input dataset. The model is able to accurately capture the historical long-term trend and interannual fluctuations over decades (from 1969 to present), using only 7 yr of monthly measurements of surface water temperature for calibration. Additionally, when used to predict future surface water temperature of the lake, air2water produces the same projections irrespective of the air temperature dataset used to drive the model. This is certainly desirable, but not immediately expected when using a relatively simple model. Overall, the results suggest the high potential and robustness of air2water as a predictive tool for climate change assessment. Lake surface temperature warming of up to 1.1°C (RCP 4.5) and 2.9°C (RCP 8.5) was simulated at the end of the 21st century during summer months in Lake Tahoe. Such a scenario, if realized, would lead to serious consequences on lake water chemistry, primary productivity, plankton community structure, and nutrient cycling.

2018 journal paper

Analysis of uncertainty sources in projecting lake surface water temperature: Application to the Laurentian Great Lakes 2018

Piccioni, F.; Piccolroaz, S.; Toffolon, M.; Majone, B., "Analysis of uncertainty sources in projecting lake surface water temperature: Application to the Laurentian Great Lakes" in Proc. of the 5th IAHR Europe Congress - New challenges in hydraulic research and engineering, Trento: 5th IAHR Europe Congress Organizers, 2018, p. 329-330. - ISBN: 978-981-11-2731-1. Proceedings of: 5th IAHR Europe Congress, Trento (Italy), 12th - 14th June 2018

2018 extended abstract

Quantifying the impact of the Three Gorges Dam on the thermal dynamics of the Yangtze River 2018

Cai, Huayang; Piccolroaz, Sebastiano; Huang, Jingzheng; Liu, Zhiyong; Liu, Feng; Toffolon, Marco, "Quantifying the impact of the Three Gorges Dam on the thermal dynamics of the Yangtze River" in ENVIRONMENTAL RESEARCH LETTERS, v. 13, n. 5 (2018), p. 054016. - URL: http://iopscience.iop.org/article/10.1088/1748-9326/aab9e0/pdf . - DOI: 10.1088/1748-9326/aab9e0

This study examines the impact of the world’s largest dam, the Three Gorges Dam (TGD), on the thermal dynamics of the Yangtze River (China). The analysis uses long-term observations of river water temperature (RWT) in four stations and reconstructs the RWT that would have occurred in absence of the TGD. Relative to pre-TGD conditions, RWT consistently warmed in the region due to air temperature (AT) increase. In addition, the analysis demonstrates that the TGD significantly affected RWT in the downstream reach. At the closest downstream station (Yichang) to the TGD, the annual cycle of RWT experienced a damped response to AT and a marked seasonal alteration: warming during all seasons except for spring and early summer which were characterized by cooling. Both effects were a direct consequence of the larger thermal inertia of themassive water volume stored in the TGD reservoir, causing the downstream reach to be more thermally resilient. The approach used here to quantify the separate contributions of climate and human interventions on RWT can be used to set scientific guidelines for river management and conservation planning strategies.

2018 journal paper

Ecogeomorphic relations between marsh surface elevation and vegetation properties in a temperate multi-species salt marsh 2017

Belliard, Jean-philippe, Laurent, Louis-marie; Temmerman, Stijn; Toffolon, Marco, "Ecogeomorphic relations between marsh surface elevation and vegetation properties in a temperate multi-species salt marsh" in EARTH SURFACE PROCESSES AND LANDFORMS, v. 42, n. 6 (2017), p. 855-865. - URL: http://onlinelibrary.wiley.com/doi/10.1002/esp.4041/abstract . - DOI: 10.1002/esp.4041

Salt marshes represent a fascinating example of an ecosystem whose dynamic response to climate change is chiefly governed by a two-way bio-physical coupling between marsh ecology and geomorphology. Relationships between vegetation biomass and marsh surface elevation, and between vegetation biomass and its physical properties that influence sedimentation rates, have been progressively formulated in the literature in order to provide mechanistic understandings and mathematical model descriptions of these ecogeomorphic feedbacks. In this study, a field survey was conducted in a temperate salt marsh grown by multiple halophyte species in order to quantify and validate these empirical relationships, yet in a location characterized by different climatic and ecological conditions from the locations where these relationships were initially derived. Regression analysis revealed that vegetation biomass can be expressed as a linearly increasing function of marsh elevation, providing therefore a direct empirical validation for such a relationship previously reported in the literature and implemented in some ecogeomorphic models. However, previously documented allometric relationships between total standing biomass and vegetation morphometrics – namely stem diameter, stem density and projected plant area per unit volume – were not confirmed by our results, which only showed an allometric scaling for stem height. These results suggest that previously documented formulations of mineral sediment trapping processes modulated by plants, which are partly derived on the basis of these allometric relationships, are not generally validated for multi-species salt marshes. Therefore, existing models that apply these process-based equations to study marsh evolution in a multi-species context may not capture in detail the vegetation-induced geomorphic work.

2017 journal paper

Large Eddy Simulation (LES) of wind-driven circulation in a peri-alpine lake: Detection of turbulent structures and implications of a complex surrounding orography 2017

Santo, Marco A.; Toffolon, Marco; Zanier, Giulia; Giovannini, Lorenzo; Armenio, Vincenzo, "Large Eddy Simulation (LES) of wind-driven circulation in a peri-alpine lake: Detection of turbulent structures and implications of a complex surrounding orography" in JOURNAL OF GEOPHYSICAL RESEARCH. OCEANS, v. 2017, n. 122 (2017), p. 4704-4722. - URL: http://onlinelibrary.wiley.com/doi/10.1002/2016JC012284/abstract . - DOI: 10.1002/2016JC012284

We investigate wind-driven circulation in a peri-alpine lake (Lake Ledro - Italy) using LES-COAST. Lake Ledro is interesting because its own dimensions are suited for LES and it is surrounded by complex orography, affecting wind distribution. We consider the winter condition when stratification is nearly absent. Two types of time-varying wind stress are used: spatially homogeneous and spatially inhomogeneous respectively. The analysis of the eddy viscosities shows substantial differences with respect to the ocean case characterized by absence of coastal boundaries and homogeneous, steady wind. The quantities exhibit a noticeable inhomogeneous behavior: the horizontal eddy viscosity is larger in the water body far from the boundaries, whereas the vertical one is larger close to the lateral boundaries due to the presence of a boundary layer. The energetic bottom boundary layer, typically occurring in lakes, is not present. This because of the intrinsic unsteadiness of the thermal wind blowing over the lake and due to the absence of large amplitude internal waves, the latter present only in case of stable stratification. In the inhomogeneous wind case, up-welling and down-welling areas are not confined along the shoreline only, but are also generated in the water body due to substantial horizontal velocity divergence, and turbulent mixing, quantified by eddy viscosities, TKE and its dissipation rate, appears enhanced with respect to the homogeneous wind case. Finally, downwelling/upwelling areas along the windward/leeward coastline respectively were observed, whose quantitative estimation may give explanation for the bloom of cyanobacteria at the lake surface observed in winter.

2017 journal paper

A plunge into the depths of Italy’s Lake Garda 2017

Toffolon, M.; Piccolroaz, S.; Dijkstra, H., "A plunge into the depths of Italy’s Lake Garda" in EOS, v. 98, (2017), p. 1-3. - URL: https://eos.org/meeting-reports/a-plunge-into-the-depths-of-italys-lake-garda . - DOI: 10.1029/2017EO074499

2017 journal paper

Ecogeomorphological feedbacks of water fluxes, sediment transport and vegetation dynamics in rivers and estuaries 2016

D'Alpaos, Andrea; Toffolon, Marco; Camporeale, Carlo, "Ecogeomorphological feedbacks of water fluxes, sediment transport and vegetation dynamics in rivers and estuaries" in ADVANCES IN WATER RESOURCES, v. 93, (2016), p. 151-155. - URL: https://www.sciencedirect.com/science/article/pii/S0309170816301567 . - DOI: 10.1016/j.advwatres.2016.05.019

2016 journal paper

Metal fate and effects in estuaries: A review and conceptual model for better understanding of toxicity 2016

de Souza Machado, Anderson Abel; Spencer, Kate; Kloas, Werner; Toffolon, Marco; Zarfl, Christiane, "Metal fate and effects in estuaries: A review and conceptual model for better understanding of toxicity" in SCIENCE OF THE TOTAL ENVIRONMENT, v. 541, (2016), p. 268-281. - URL: www.elsevier.com/locate/scitotenv https://www.sciencedirect.com/science/article/pii/S0048969715307051?via%3Dihub . - DOI: 10.1016/j.scitotenv.2015.09.045

Metal pollution is a global problemin estuaries due to the legacy of historic contamination and currently increasing metal emissions. However, the establishment of water and sediment standards or management actions in brackish systems has been difficult because of the inherent transdisciplinary nature of estuarine processes. According to the European Commission, integrative comprehension of fate and effects of contaminants in different compartments of these transitional environments (estuarine sediment, water, biota) is still required to better establish, assess and monitor the good ecological status targeted by the Water Framework Directive. Thus, the present study proposes a holistic overview and conceptual model for the environmental fate of metals and their toxicity effects on aquatic organisms in estuaries. This includes the analysis and integration of biogeochemical processes and parameters, metal chemistry and organism physiology. Sources of particulate and dissolved metal, hydrodynamics, water chemistry, and mechanisms of toxicity are discussed jointly in a multidisciplinary manner. It is also hypothesized how these different drivers of metal behaviour might interact and affect metal concentrations in diverse media, and the knowledge gaps and remaining research challenges are pointed. Ultimately, estuarine physicochemical gradients, biogeochemical processes, and organismphysiology are jointly coordinating the fate and potential effects of metals in estuaries, and both realistic model approaches and attempts to postulate site-specific water criteria or water/sediment standards must consider such interdisciplinary interactions. © 2015 Elsevier B.V. All rights reserved.

2016 journal paper

Prediction of river water temperature: a comparison between a new family of hybrid models and statistical approaches 2016

Piccolroaz, Sebastiano; Elisa, Calamita; Majone, Bruno; Aurélien, Gallice; Annuziato, Siviglia; Toffolon, Marco, "Prediction of river water temperature: a comparison between a new family of hybrid models and statistical approaches" in HYDROLOGICAL PROCESSES, v. 30, n. 21 (2016), p. 3901-3917. - URL: https://onlinelibrary.wiley.com/doi/abs/10.1002/hyp.10913 . - DOI: 10.1002/hyp.10913

River water temperature is a key physical variable controlling several chemical, biological and ecological processes. Its reliable prediction is a main issue in many environmental applications, which however is hampered by data scarcity, when using datademanding deterministic models, and modelling limitations, when using simpler statistical models. In this work we test a suite of models belonging to air2stream family, which are characterized by a hybrid formulation that combines a physical derivation of the key equation with a stochastic calibration of parameters. The air2stream models rely solely on air temperature and streamflow, and are of similar complexity as standard statistical models. The performances of the different versions of air2stream in predicting river water temperature are compared with those of the most common statistical models typically used in the literature. To this aim, a dataset of 38 Swiss rivers is used, which includes rivers classified into four different categories according to their hydrological characteristics: low-land natural rivers, lake outlets, snow-fed rivers and regulated rivers. The results of the analysis provide practical indications regarding the type of model that is most suitable to simulate river water temperature across different time scales (from daily to seasonal) and for different hydrological regimes. A model intercomparison exercise suggests that the family of air2stream hybrid models generally outperforms statistical models, while cross-validation conducted over a 30-year period indicates that they can be suitably adopted for long-term analyses. Copyright © 2016 John Wiley & Sons, Ltd.

2016 journal paper

Interactions between river stage and wetland vegetation detected with a Seasonality Index derived from LANDSAT images in the Apalachicola delta, Florida 2016

la Cecilia, Daniele; Toffolon, Marco; Woodcock, Curtis E.; Fagherazzi, Sergio, "Interactions between river stage and wetland vegetation detected with a Seasonality Index derived from LANDSAT images in the Apalachicola delta, Florida" in ADVANCES IN WATER RESOURCES, v. 89, (2016), p. 10-23. - URL: https://www.sciencedirect.com/science/article/pii/S0309170815300142 . - DOI: 10.1016/j.advwatres.2015.12.019

The distribution of swamp floodplain vegetation and its evolution in the lower non-tidal reaches of the Apalachicola River, Florida USA, is mapped using Landsat Thematic Mapper and Enhanced Thematic Mapper Plus (TM/ETM+) images captured over a period of 29 years. A newly developed seasonality index (SI), the ratio of the NDVI in winter months to the summer months, shows that the hardwood swamp, dominated by bald cypress and water tupelo, is slowly replaced by bottomland hardwood forest. This forest shift is driven by lower water levels in the Apalachicola River in the last 30 years, and predominantly occurs in the transitional area between low floodplains and high river banks. A negative correlation between maximum summer NDVI and water levels in winter suggests the growth of more vigorous vegetation in the vicinity of sloughs during years with low river flow. A negative correlation with SI further indicates that these vegetation patches are possibly replaced by species typical of drier floodplain conditions. © 2015 Elsevier Ltd. All rights reserved

2016 journal paper

Sediment and vegetation spatial dynamics facing sea-level rise in microtidal salt marshes: Insights from an ecogeomorphic model 2016

Belliard, Jean-philippe, Laurent, Louis-marie; Di Marco, Nicola; Carniello, Luca; Toffolon, Marco, "Sediment and vegetation spatial dynamics facing sea-level rise in microtidal salt marshes: Insights from an ecogeomorphic model" in ADVANCES IN WATER RESOURCES, v. 93, (2016), p. 249-264. - URL: https://www.sciencedirect.com/science/article/pii/S030917081500295X . - DOI: 10.1016/j.advwatres.2015.11.020

Modeling effort s have considerably improved our understanding on the chief processes that govern the evolution of salt marshes under climate change. Yet the spatial dynamic response of salt marshes to sea-level rise that results from the interactions between the tidal landforms of interest and the presence of bio-geomorphic features has not been addressed explicitly. Accordingly, we use a modeling framework that integrates the co- evolution of the marsh platform and the embedded tidal networks to study sea-level rise effects on spatial sediment and vegetation dynamics in microtidal salt marshes considering different ecological scenarios. The analysis unveils mechanisms that drive spatial variations in sedimentation rates in ways that increase marsh resilience to rising sea-levels. In particular, marsh survival is related to the effectiveness of transport of sediments toward the interior marshland. This study hints at additional dynamics related to the modulation of channel cross-sections affecting sediment advection in the channels and subsequent delivery in the inner marsh, which should be definitely considered in the study of marsh adaptability to sea-level rise and posterior management. ©2015 Elsevier Ltd. All rights reserved.

2016 journal paper

An analytical approach to determining resonance in semi-closed convergent tidal channels 2016

Cai, Huayang; Toffolon, Marco; Savenije, Hubert H. G., "An analytical approach to determining resonance in semi-closed convergent tidal channels" in COASTAL ENGINEERING JOURNAL, v. 58, n. 3 (2016), p. 1650009-1-1650009-37. - URL: https://www.tandfonline.com/doi/abs/10.1142/S0578563416500091 . - DOI: 10.1142/S0578563416500091

An analytical model is used to investigate the resonant behavior in a semi-closed channel. The main integral quantities of the tidal wave are obtained by means of a linearized one-dimensional model as a function of three dimensionless parameters, representing cross-section convergence, friction and distance to the closed boundary. Arbitrary along-channel variations of width and depth are accounted for by using a multi-reach approach, whereby the main tidal dynamics are reconstructed by solving a set of linear equations satisfying the continuity conditions of water level and discharge at the junctions of the sub-reaches. We highlight the importance of depth variation in the momentum equation, which is not considered in the classical tidal theory. The model allows for a direct characterization of the resonant response and for the understanding of the relative importance of the controlling parameters, highlighting the role of convergence and friction. Subsequently, the analytical model is applied to the Bristol Channel and the Guadalquivir estuary. The proposed analytical relations provide direct insights into the tidal resonance in terms of tidal forcing, geometry and friction, which will be useful for the study of semi-closed tidal channels that experience relatively large tidal ranges at the closed end.

2016 journal paper

Biomorphodynamic modelling of inner bank advance in migrating meander bends 2016

Zen, Simone; Zolezzi, Guido; Toffolon, Marco; Gurnell, Angela M., "Biomorphodynamic modelling of inner bank advance in migrating meander bends" in ADVANCES IN WATER RESOURCES, v. 93, (2016), p. 166-181. - URL: https://www.sciencedirect.com/science/article/pii/S0309170815002924 . - DOI: 10.1016/j.advwatres.2015.11.017

We propose a bio-morphodynamic model at bend cross-sectional scale for the lateral migration of river meander bends, where the two banks can migrate separately as a result of the mutual interaction between river flow, sediments and riparian vegetation, particularly at the interface between the permanently wet channel and the advancing floodplain. The model combines a non-linear analytical model for the morphodynamic evolution of the channel bed, a quasi-1D model to account for flow unsteadiness, and an ecological model describing riparian vegetation dynamics. Simplified closures are included to estimate the feedbacks among vegetation, hydrodynamics and sediment transport, which affect the morphology of the river-floodplain system. Model tests reveal the fundamental role of riparian plants in generating bio-morphological patterns at the advancing floodplain margin. Importantly, they provide insight into the biophysical controls of the ‘bar push’ mechanism and into its role in the lateral migration of meander bends and in the temporal variations of the active channel width. ©2015 Elsevier Ltd. All rights reserved.

2016 journal paper

Comparing simple models to predict river water temperature 2016

Piccolroaz, Sebastiano; Calamita, Elisa; Majone, Bruno; Gallice, Aurélien; Siviglia, Annunziato; Toffolon, Marco, "Comparing simple models to predict river water temperature" in 33rd SIL Congress - Book of Abstracts, Torino: SIL - International Society of Limnology, 2016, p. 228-228. Proceedings of: SIL2016, Torino, 31st July - 05th August 2016. - URL: http://www.sil2016.it/files/3214/7272/2565/33rd_SIL_Congress_2016_-_Book_of_Abstracts.pdf

2016 extended abstract

Editorial 2016

Toffolon, Marco, "Editorial" in WATER MANAGEMENT, v. 169, n. 5 (2016), p. 199-200. - URL: https://www.icevirtuallibrary.com/doi/pdf/10.1680/jwama.2016.169.5.199 . - DOI: 10.1680/jwama.2016.169.5.199

2016 journal paper

Minimal model for double diffusion and its application to Kivu, Nyos, and Powell Lake 2015

Toffolon, Marco; Wüest, Alfred; Sommer, Tobias, "Minimal model for double diffusion and its application to Kivu, Nyos, and Powell Lake" in JOURNAL OF GEOPHYSICAL RESEARCH. OCEANS, v. 120, n. 9 (2015), p. 6202-6224. - URL: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JC010970 . - DOI: 10.1002/2015JC010970

Double diffusion originates from the markedly different molecular diffusion rates of heat and salt in water, producing staircase structures under favorable conditions. The phenomenon essentially consists of two processes: molecular diffusion across sharp interfaces and convective transport in the gravitationally unstable layers. In this paper, we propose a model that is based on the one‐dimensional description of these two processes only, and—by self‐organization—is able to reproduce both the large‐scale dynamics and the structure of individual layers, while accounting for different boundary conditions. Two parameters characterize the model, describing the time scale for the formation of unstable water parcels and the optimal spatial resolution. Theoretical relationships allow for the identification of the influence of these parameters on the layer structure and on the mass and heat fluxes. The performances of the model are tested for three different lakes (Powell, Kivu, and Nyos), showing a remarkable agreement with actual microstructure measurements.

2015 journal paper

A hybrid model for river water temperature as a function of air temperature and discharge 2015

Toffolon, Marco; Piccolroaz, Sebastiano, "A hybrid model for river water temperature as a function of air temperature and discharge" in ENVIRONMENTAL RESEARCH LETTERS, v. 10, n. 11 (2015), p. 114011. - URL: http://iopscience.iop.org/issue/1748-9326/10/11 . - DOI: 10.1088/1748-9326/10/11/114011

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 1oC, 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.

2015 journal paper

HOW LAKES RESPOND TO AIR TEMPERATURE CHANGES: A LUMPED MODEL FOR LONG-TERM PREDICTIONS 2015

Toffolon, Marco; Piccolroaz, Sebastiano; Majone, Bruno, "HOW LAKES RESPOND TO AIR TEMPERATURE CHANGES: A LUMPED MODEL FOR LONG-TERM PREDICTIONS" in ASLO 2015 Aquatic Sciences Meeting: PROGRAM BOOK, Waco, Texas: ASSOCIATION FOR THE SCIENCES OF LIMNOLOGY AND OCEANOGRAPHY, 2015. Proceedings of: ASLO 2015, Granada, Spain, 22-27/02/2015. - URL: https://www.sgmeet.com/aslo/granada2015/static/files/aslo2015-pgmbk-web.pdf

2015 extended abstract