Research

27 pages, 6578 KiB

Open AccessArticle

Hydrogeomorphic Scaling and Ecohydraulics for Designing Rescaled Channel and Floodplain Geometry in Regulated Gravel–Cobble Bed Rivers for Pacific Salmon Habitat

by Rocko A. Brown

Water 2022, 14(4), 670; https://doi.org/10.3390/w14040670 - 21 Feb 2022

Cited by 3 | Viewed by 2954

Abstract

Societies are increasingly restoring and/or rehabilitating rivers below dams for keystone species such as salmon. A fundamental concept for rehabilitating river morphology below dams for salmon is that a rescaled version of the river corridor synchronized to the regulated flow regime can restore [...] Read more.

Societies are increasingly restoring and/or rehabilitating rivers below dams for keystone species such as salmon. A fundamental concept for rehabilitating river morphology below dams for salmon is that a rescaled version of the river corridor synchronized to the regulated flow regime can restore habitat quantity and quality. Downscaled and resized hydrographs have been shown to provide environmental benefits to fish communities including salmon as well as riparian vegetation communities. However, less research exists on how this can be achieved through the topographic rescaling of heavily modified and regulated river corridors. The goal of this paper is to review analytical methods to determine initial of size of rescaled channel and floodplain mesohabitat units in regulated gravel–cobble bed rivers for Pacific salmon (Oncorhynchus spp.) habitat using hydrogeomorphic scaling and ecohydraulics. Hydrogeomorphic flow scaling is the prediction of river morphology and geometry using empirical and analytical relationships. Ecohydraulic scaling refers to the use of ecohydrology, habitat suitability curves, and fish density relationships to determine the size of mesohabitat units for ecologically relevant flows. In practice, these are complimentary first order estimates of channel and floodplain configurations followed by iterative design in a hierarchical manner. This review advances the science of river design by synthesizing these complimentary ideologies for Pacific salmon habitat restoration in regulated rivers. Following the review, the layout of features is briefly discussed followed by a discussion of important considerations beyond the physical and topographic rescaling of river corridors for salmonid habitat restoration. Full article

(This article belongs to the Special Issue Fluvial Hydraulics and Applications)

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19 pages, 5229 KiB

Open AccessArticle

Hydraulic Efficiency of Green-Blue Flood Control Scenarios for Vegetated Rivers: 1D and 2D Unsteady Simulations

by Giuseppe Francesco Cesare Lama, Matteo Rillo Migliorini Giovannini, Alessandro Errico, Sajjad Mirzaei, Roberta Padulano, Giovanni Battista Chirico and Federico Preti

Water 2021, 13(19), 2620; https://doi.org/10.3390/w13192620 - 23 Sep 2021

Cited by 39 | Viewed by 2826

Abstract

Flood hazard mitigation in urban areas crossed by vegetated flows can be achieved through two distinct approaches, based on structural and eco-friendly solutions, referred to as grey and green–blue engineering scenarios, respectively; this one is often based on best management practices (BMP) and [...] Read more.

Flood hazard mitigation in urban areas crossed by vegetated flows can be achieved through two distinct approaches, based on structural and eco-friendly solutions, referred to as grey and green–blue engineering scenarios, respectively; this one is often based on best management practices (BMP) and low-impact developments (LID). In this study, the hydraulic efficiency of two green–blue scenarios in reducing flood hazards of an urban area crossed by a vegetated river located in Central Tuscany (Italy), named Morra Creek, were evaluated for a return period of 200 years, by analyzing the flooding outcomes of 1D and 2D unsteady hydraulic simulations. In the first scenario, the impact of a diffuse effect of flood peak reduction along Morra Creek was assessed by considering an overall real-scale growth of common reed beds. In the second scenario, riverine vegetation along Morra Creek was preserved, while flood hazard was mitigated using a single vegetated flood control area. This study demonstrates well the benefits of employing green–blue solutions for reducing flood hazards in vegetated rivers intersecting agro-forestry and urban areas while preserving their riverine ecosystems. It emerged that the first scenario is a valuable alternative to the more impacting second scenario, given the presence of flood control areas. Full article

(This article belongs to the Special Issue Fluvial Hydraulics and Applications)

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22 pages, 30642 KiB

Open AccessArticle

Silting in the Grand Canal in the Domain of Chantilly (Oise, France)—Catchment-Scale Hydrogeomorphological Reconnaissance and Local-Scale Hydro-Sedimentary Transport Modelling

by Guillaume G. Chevalier, Florent Locatelli, Eric Masson and Olivier Blanpain

Water 2021, 13(14), 1989; https://doi.org/10.3390/w13141989 - 20 Jul 2021

Viewed by 2225

Abstract

The domain of Chantilly (Oise, France) includes a castle and a garden, both dating from the eighteenth century, which are seen as important legacies of France’s history. Nowadays, the 2.5 km canal that runs through the domain is subject to the phenomenon of [...] Read more.

The domain of Chantilly (Oise, France) includes a castle and a garden, both dating from the eighteenth century, which are seen as important legacies of France’s history. Nowadays, the 2.5 km canal that runs through the domain is subject to the phenomenon of silting, leading to the accumulation of sediments within the canal linked to the proliferation of algae, which has a dissuasive effect among visitors. HEC-RAS software (Hydrologic Engineering Centers River Analysis System, US army corps of Engineers, Washington, D.C., USA) was used to model and understand sediment accumulation within the canal. This model is widely used in the literature tackling sediment transport and accumulation, and allows the forecasting of which stretches of the canal are most susceptible to sediment accumulation. The simulation results highlight an accumulation of sediment near the entrance of the Nonette stream into the canal and a propagation through the canal. The total accumulated volume assessed by the model between 2001 and 2010 equals 3901 m³, when the reconnaissance of the catchment showed the sediment was not a limiting factor. However, the volumes determined are underestimated, as matter brought by vegetation or other systems different from the river (e.g., wind, rainfall) is not considered in the calculation. The quantity of sediment is also subject to uncertainties, as the bathymetry of the canal is not available. Full article

(This article belongs to the Special Issue Fluvial Hydraulics and Applications)

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24 pages, 10071 KiB

Open AccessFeature PaperArticle

Comparative Analysis of HLLC- and Roe-Based Models for the Simulation of a Dam-Break Flow in an Erodible Channel with a 90^∘ Bend

by Sergio Martínez-Aranda, Robin Meurice, Sandra Soares-Frazão and Pilar García-Navarro

Water 2021, 13(13), 1840; https://doi.org/10.3390/w13131840 - 01 Jul 2021

Cited by 4 | Viewed by 2342

Abstract

In geophysical surface flows, the sediment particles can be transported under capacity (equilibrium) conditions or noncapacity (nonequilibrium) conditions. On the one hand, the equilibrium approach for the bedload transport assumes that the actual transport rate instantaneously adapts to the local flow features. The [...] Read more.

In geophysical surface flows, the sediment particles can be transported under capacity (equilibrium) conditions or noncapacity (nonequilibrium) conditions. On the one hand, the equilibrium approach for the bedload transport assumes that the actual transport rate instantaneously adapts to the local flow features. The resulting system of equations, composed of the shallow water equations for the flow (SWE) and the Exner equation for the bed evolution, has been widely used to simulate bedload processes. These capacity SWE + Exner models are highly dependent on the setup parameters, so that the calibration procedure often disguises the advantages and flaws of the numerical method. On the other hand, noncapacity approaches account for the temporal and spatial delay of the actual sediment transport rate with respect to the capacity of the flow. The importance of assuming nonequilibrium conditions in bedload numerical models remains uncertain however. In this work, we compared the performances of three different strategies for the resolution of the SWE + Exner system under capacity and noncapacity conditions to approximate a set of experimental data with fixed setup parameters. The results indicate that the discrete strategy used to compute the intercell fluxes significantly affected the solution. Furthermore, the noncapacity approach can improve the model prediction in regions with complex transient processes, but it requires a careful calibration of the nonequilibrium parameters. Full article

(This article belongs to the Special Issue Fluvial Hydraulics and Applications)

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12 pages, 6724 KiB

Open AccessArticle

Turbulent Flow Structure in a Confluence: Influence of Tributaries Width and Discharge Ratios

by Leila Alizadeh and João Fernandes

Water 2021, 13(4), 465; https://doi.org/10.3390/w13040465 - 11 Feb 2021

Cited by 3 | Viewed by 2836

Abstract

River channel confluences are rather important interfaces where intense changes in physical, mixing and sediment transport processes occur. Following an experimental campaign, the main flow mechanisms in confluences and the development of the shear layer formed between the two tributary flows are presented. [...] Read more.

River channel confluences are rather important interfaces where intense changes in physical, mixing and sediment transport processes occur. Following an experimental campaign, the main flow mechanisms in confluences and the development of the shear layer formed between the two tributary flows are presented. As the experimental flow cases comprised changes in the flow discharge and channel widths of the tributaries, the influence of width and discharge ratios on the turbulent flow structure and shear layer is also evaluated. Main findings indicate that changes in the difference between momentum ratio in the tributaries have a significant effect on the magnitude and location of flow mechanisms. Full article

(This article belongs to the Special Issue Fluvial Hydraulics and Applications)

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20 pages, 7380 KiB

Open AccessFeature PaperArticle

Impact Force of a Geomorphic Dam-Break Wave against an Obstacle: Effects of Sediment Inertia

by Cristiana Di Cristo, Massimo Greco, Michele Iervolino and Andrea Vacca

Water 2021, 13(2), 232; https://doi.org/10.3390/w13020232 - 19 Jan 2021

Cited by 2 | Viewed by 2226

Abstract

The evaluation of the impact force on structures due to a flood wave is of utmost importance for estimating physical damage and designing adequate countermeasures. The present study investigates, using 2D shallow-water approximation, the morphodynamics and forces caused by a dam-break wave against [...] Read more.

The evaluation of the impact force on structures due to a flood wave is of utmost importance for estimating physical damage and designing adequate countermeasures. The present study investigates, using 2D shallow-water approximation, the morphodynamics and forces caused by a dam-break wave against a rigid obstacle in the presence of an erodible bed. A widely used coupled equilibrium model, based on the two-dimensional Saint–Venant hydrodynamic equations combined with the sediment continuity Exner equation (SVEM), is compared with a more complex two-phase model (TPM). Considering an experimental set-up presented in the literature with a single rigid obstacle in a channel, two series of tests were performed, assuming sand or light sediments on the bottom. The former test is representative of a typical laboratory experiment, and the latter may be scaled up to a field case. For each test, two different particle diameters were considered. Independently from the particle size, it was found that in the sand tests, SVEM performs similarly to TPM. In the case of light sediment, larger differences are observed, and the SVEM predicts a higher force of about 26% for both considered diameters. The analysis of the flow fields and the morphodynamics shows these differences can be essentially ascribed to the role of inertia of the solid particles. Full article

(This article belongs to the Special Issue Fluvial Hydraulics and Applications)

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17 pages, 6111 KiB

Open AccessArticle

Structural Properties of the Static Armor during Formation and Reestablishment in Gravel-Bed Rivers

by Qiang Wang, Yunwen Pan, Kejun Yang and Ruihua Nie

Water 2020, 12(7), 1845; https://doi.org/10.3390/w12071845 - 28 Jun 2020

Cited by 4 | Viewed by 1670

Abstract

The formation and reestablishment of bed structural properties in the static armor layer is an important research subject. To address this issue, we conducted a series of static armor layer experiments in a laboratory flume that focused on formation and reestablishment. Through an [...] Read more.

The formation and reestablishment of bed structural properties in the static armor layer is an important research subject. To address this issue, we conducted a series of static armor layer experiments in a laboratory flume that focused on formation and reestablishment. Through an automatic measurement system, we obtained a real-time bed load transport rate. The bed surface elevation at different flow intensities was obtained using a PTS (Photo Terrain Scanning) system. The results show that the formation and reestablishment of the bed load transport rate in the static armor layer increased from zero to its peak before decaying. The bed structure response was found to be highly dependent on the unevenness of the bed surface elevation. The bed surface elevation of a static armor layer in a laboratory flume is considered as a two-dimensional random field. In a two-dimensional random field, the changes in bed elevation are characterized using statistical parameters. Statistical parameters are evaluated from precise digital elevation models (DEMs) of bed surfaces. Experimental results provide the change of probability distribution functions (PDFs) and second-order structure functions of bed elevations between formation and reestablishment after breaking the static armor layer. By quantitatively analyzing the changes in these statistical parameters, we quantified the difference between the bed structure in the static armor layer formation and the new static armor layer formed after being broken. Thus, this finding reveals that the bed structure of the static armor layer formed by different flow intensities is different, and this difference can be quantified using statistical methods. Full article

(This article belongs to the Special Issue Fluvial Hydraulics and Applications)

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13 pages, 1451 KiB

Open AccessArticle

Discharge Estimation Using Tsallis and Shannon Entropy Theory in Natural Channels

by Jitendra Kumar Vyas, Muthiah Perumal and Tommaso Moramarco

Water 2020, 12(6), 1786; https://doi.org/10.3390/w12061786 - 23 Jun 2020

Cited by 12 | Viewed by 2332

Abstract

Streamflow measurements during high floods is a challenge for which the World Meteorological Organization fosters the development of innovative technologies for achieving an accurate estimation of the discharge. The use of non-contact sensors for monitoring surface flow velocities is of interest to turn [...] Read more.

Streamflow measurements during high floods is a challenge for which the World Meteorological Organization fosters the development of innovative technologies for achieving an accurate estimation of the discharge. The use of non-contact sensors for monitoring surface flow velocities is of interest to turn these observed values into a cross-sectional mean flow velocity, and subsequently, into discharge if bathymetry is given. In this context, several techniques are available for the estimation of mean flow velocity, starting from observed surface velocities. Among them, the entropy-based methodology for river discharge assessment is often applied by leveraging the theoretical entropic principles of Shannon and Tsallis, both of which link the maximum flow velocity measured at a vertical of the flow area, named the y-axis, and the cross-sectional mean flow velocity at a river site. This study investigates the performance of the two different entropic approaches in estimating the mean flow velocity, starting from the maximum surface flow velocity sampled at the y-axis. A velocity dataset consisting of 70 events of measurements collected at two gauged stations with different geometric and hydraulic characteristics on the Po and Tiber Rivers in Italy was used for the analysis. The comparative evaluation of the velocity distribution observed at the y-axis of all 70 events of measurement was closely reproduced using both the Shannon and Tsallis entropy approaches. Accurate values in terms of the cross-sectional mean flow velocity and discharge were obtained with average errors not exceeding 10%, demonstrating that the Shannon and Tsallis entropy concepts were equally efficient for discharge estimation in any flow conditions. Full article

(This article belongs to the Special Issue Fluvial Hydraulics and Applications)

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