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Open Channel Flows: An Open Topic That Requires Further Exploration

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A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Hydraulics and Hydrodynamics".

Deadline for manuscript submissions: closed (20 March 2025) | Viewed by 2864

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Dr. Mouldi Ben Meftah

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Department of Civil, Environmental, Land, Building Engineering and Chemistry, Polytechnic University of Bari, Via E. Orabona 4, 70125 Bari, Italy
Interests: open channel flows; hydrodynamics; turbulent flows; vegetated channels; hydraulic structures; local scouring; hydraulic jumps; boundary layers; experimental and numerical modeling; coastal monitoring; maritime hydraulics
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Special Issue Information

Dear Colleagues,

Rivers, valleys, waterways, streams, streamlets, creeks, tributaries, flumes, sewers, spillways, drains, canals, ditches, lakes, estuaries, etc., are frequently present in our environment. They are all open channel flows and are the most common major drainage system on Earth. They are natural or man-made conveyance systems for stormwater, surface water, wastewater, and groundwater. The free-surface flow in an open channel is driven by gravity and is essentially contained within the channel boundaries. The channel characteristics, i.e., the cross/section shape, roughness, bottom slope, sediment types, constriction, presence of vegetation, and obstruction (with natural bodies or hydraulic structures), strongly influence the hydrodynamic flow structures. The flow interactions with these channel features lead to complex dynamic phenomena that may not be easily explained with simple parameterizations and theoretical descriptions.

This Special Issue aims to collect new studies on hydrodynamic structures in open channel flows and develop recent ideas and research directions on waterway ecosystems' restoration and sustainable management.

I cordially invite you to participate in this Special Issue by submitting your recent works on this topic, such as experimental and/or numerical modeling of turbulent flow in rivers and open channels, flow–vegetation interaction, scouring processes, wastewater discharge in cross flows, mixing and dispersion of contaminants, meandering streams, flow–boundary interaction, estuary dynamics, river flooding management, and many other themes.

Dr. Mouldi Ben Meftah
Guest Editor

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Water is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

open channel flows
experimental and numerical modeling
vegetated channels
scouring processes
turbulence
mixing processes
estuary dynamics
river flooding
boundary layers
meandering streams

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Published Papers (3 papers)

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Research

19 pages, 9716 KiB

Open AccessArticle

Turbulent and Subcritical Flows over Macro-Roughness Elements

by Francisco Martínez and Javier Farías

Water 2025, 17(9), 1301; https://doi.org/10.3390/w17091301 - 27 Apr 2025

Viewed by 131

Abstract

Determining the friction coefficients for uniform flows over very rough bottoms is a long-standing problem in open-channel hydraulics and river engineering. This experimental study presents measurements of the surface deformation as well as Darcy–Weisbach and Manning friction coefficients for steady, turbulent (6058 [...] Read more.

\leq R e \leq

28,502), and subcritical flows (0.14

\leq F r \leq

0.52) over large roughness elements, where

F r

and

R e

denote the Froude and Reynolds numbers, respectively. The experiments were conducted in a rectangular, inclined flume with a train of half-cylinders mounted on the bed, with radii in the range 20 mm

\leq a \leq

50 mm. These obstacles yield a relative submergence 1.45

\leq h_{N} / a \leq

4.41 and a constant spacing ratio

e / a = 12.8

across all experimental runs, where

h_{N}

and e denote the normal flow depth and the center-to-center spacing between cylinders, respectively. The relative amplitude of the surface profiles, (

Δ h / a

), was analyzed and found to correlate strongly with

h_{N} / a

R e

and

F r

. The results reveal very high values of the Darcy friction factor, f, which follows scaling laws of the form

{f \propto (h_{N} / a)}^{\hat{n}}

, with

\hat{n} < 0

, independent of a, and

{f \propto R e}^{β}

, where

β < 0

is closely linked to a. Scaling relationships for the Manning roughness coefficient, (n), were also investigated and are reported herein. Full article

(This article belongs to the Special Issue Open Channel Flows: An Open Topic That Requires Further Exploration)

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15 pages, 3318 KiB

Open AccessArticle

Designing Long-Throated Flumes for Improved Water Management in Rice Cultivation: A New Automated Approach

by María Fátima Moreno-Pérez, Francisco Javier Pérez-Ardoy and José Roldán-Cañas

Water 2025, 17(8), 1137; https://doi.org/10.3390/w17081137 - 10 Apr 2025

Viewed by 168

Abstract

Rice is irrigated by flooding, maintaining constant water levels and achieving high water requirements. At the outlet of the plot is a drainage canal whose monitoring using a long-throated flume to determine the flow rate leaving the plot allows for the establishment of practices to reduce highwater consumption. Since the drainage channel has a trapezoidal cross-section and is built on land, the throat of the flume is also trapezoidal to ease the transition between the two sections and to reduce head losses. Herein, a new accurate procedure is developed that provides a quick and automated design of a long-throated flume. This method allows direct calculation of the dimensions of the narrowed section, side slope, and bottom width by choosing the modular limit, the sill height, and the length of the throat based on the characteristics of the channel where the flume is to be installed. The new process is applied to the design of a long-throated flume that allows us to measure the entire range of flow rates required. The design developed based on our methodology is evaluated using the WinFlume Version 2.1 software, and the results obtained demonstrate its strength and suitability. The modular limit values considered (between 0.5 and 0.8) ensure a significant reduction in head losses as water passes through. Full article

(This article belongs to the Special Issue Open Channel Flows: An Open Topic That Requires Further Exploration)

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Figure 1

20 pages, 7073 KiB

Open AccessArticle

Flow Characteristics in Partly Vegetated Channels: An Experimental Investigation

by Mouldi Ben Meftah, Danish Ali Bhutto, Diana De Padova and Michele Mossa

Water 2024, 16(6), 798; https://doi.org/10.3390/w16060798 - 7 Mar 2024

Cited by 2 | Viewed by 1926

Abstract

In this study, we attempt to experimentally investigate the flow turbulence structure in a partly vegetated channel. To achieve the objective of this study, we conducted extensive measurements of flow velocities within and outside the vegetated area, where the flow is fully developed. The experiments were conducted in a very large channel at the Coastal Engineering Laboratory of the Department of Civil, Environmental, Building Engineering and Chemistry at the Polytechnic University of Bari, Italy. The instantaneous three flow velocity components were accurately measured using a 3D-Acoustic Doppler Velocimeter (ADV)-Vectrino system at high frequency. Flow behaviors through the vegetated area, at the interface, and in the unobstructed area were analyzed via time-averaged velocities, turbulence intensity, correlation properties, spectral analysis, and vortex identification. Experimental results showed the development of three distinct characteristic flow zones: (i) a vegetated area of low streamwise velocity, high turbulence intensities, dominant inward interactions, and more intense power spectrum, (ii) a shear layer zone of increasing streamwise velocity, more enhanced transverse flow motion, exponential decrease in turbulence intensities, and frequent ejection and/or outward interaction events, and (iii) a free-stream zone of higher and almost constant streamwise velocity, lower turbulence intensities, frequent sweep and/or inward interaction events, and less intense streamwise power spectrum. The results brought further insights into the flow behaviors in these characteristic flow zones. The extensive and detailed measured data can provide a basis for improving and calibrating numerical simulations of partly vegetated channels. Full article

(This article belongs to the Special Issue Open Channel Flows: An Open Topic That Requires Further Exploration)

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