**Contents**


### **About the Editor**

**Jaan H. Pu** Dr Pu received both his BEng (1st Class Honours) and PhD degrees from the University of Bradford in 2003 and 2008, respectively. Since 2008, he has taken up several research and faculty positions at various universities/institutions around the world. He was appointed as a Lecturer in Civil Engineering at the University of Bradford in 2014; as Senior Lecturer in 2017; and as Associate Professor in 2020. Dr Pu's research concentrates on numerical and laboratory approaches to representing various water engineering applications which, include natural compound riverine flow, sediment transport, scouring, water quality, and vegetated flow. His research outputs have led to several high-quality journal articles (50+), conference proceedings (10+), edited books (2), and book chapters (2). He is currently supervising four PhD students at Bradford (three as their principal supervisor) who are investigating river hydrodynamics and sediment transport applications. He has also been appointed as the Leading Guest Editor of Special Issues, such as The Urban Fluvial and Hydro-Environment System (Frontiers in Environmental Science), Environmental Sediment Transport: Methods and Applications (MDPI Fluids), and Environmental Hydraulics, Turbulence and Sediment Transport (MDPI Fluids); and as the Guest Editor of a Special Issue on Advances in Modelling and Prediction on the Impact of Human Activities and Extreme Events on Environments (MDPI Water). He is currently a Visiting Scientist at Tsinghua University and Nanyang Technological University. He has been involved as a reviewer for several internationally well-reputed journals.

### **Preface to "Environmental Hydraulics, Turbulence and Sediment Transport"**

In the research on environmental hydraulics, its turbulence and sediment transport, constant challenges have been faced. The complexity of hydraulic impacts towards sediment morphology and turbulent flow properties makes research in this area a difficult task. However, due to pressure from climate change and the mounting issue of pollution, environmental flow studies are more crucial than ever.

Bedforming within rivers is a complex process that can be influenced by the hydraulics, vegetated field, and various suspended and bedload transports. Changes in flow conditions due to rain and flood can further complicate a hydraulic system. To date, the turbulence, morphologic, and bedforming characteristics of natural environmental flows are still not well understood.

This book aims to bring together a collection of state-of-the-art research and technologies to form a useful guide for the related research and engineering communities. It is useful for authorities and researchers interested in environmental and civil engineering studies, as well as for river and water engineers to understand the current state-of-the-art practices in environmental flow modelling, measurement and management. It is also a good resource for research, post-, or undergraduate students who wish to know about the most up-to-date knowledge in this field.

> **Jaan H. Pu** *Editor*

### *Editorial* **Environmental Hydraulics, Turbulence and Sediment Transport**

**Jaan H. Pu**

> Faculty of Engineering and Informatics, University of Bradford, Bradford DB7 1DP, UK; j.h.pu1@bradford.ac.uk; Tel.: +44-01274234556

> Within the environmental flows, i.e., river and canal networks or irrigation systems, hydraulic properties for water flow are usually impacted by eddies and sediment transport. Thus, the accuracy in predicting natural environmental flow behaviour is heftily related to the precise knowledge on its morphological characteristics under naturally occurring turbulence circumstances. The deposition and erosion under sediment-laden flow also play a crucial role in how the natural flows and watercourses are supposed to be managed to alleviate and avoid disastrous pollution transport.

> In a previous Special Issue (SI) of *Fluids* entitled "Environmental Sediment Transport: Methods and Applications", the sediment transport phenomenon has been explored in the applications of natural bedform (Pu [1]) and deposition within rainwater (John et al. [2]). As a continuation, the leading gues<sup>t</sup> editor for that SI decided to launch a new volume to further advance and expand on the discussion topics. This SI, which contains a collection of seven papers, gathers recent advances in the fields of environmental hydraulics, turbulence and sediment transport from various international authors/researchers to tackle the abovementioned important and pressing environmental issues.

> Owing to the fact that suspended solid transport is among the important factors to alleviate pollutant propagation, its mathematical modelling has been intensely investigated in recent literature studies. In the review work by Wallwork et al. [3], the previous research on mathematical modelling of suspended sediment transport has been summarised and analysed. Besides numerical models, the suggested analytical approaches in the literature to represent the suspended load have also been reviewed. Wallwork et al.'s study increases the potential for researchers to learn from previous experiences and studies in order to move towards the goal for accurate sediment transport modelling.

> Sediment-laden condition is regarded as one of the key mechanisms to the formation of rough bedform in natural flow (Pu [1]). To add to the complexity, any obstruction like wood-log or boulder, in particular those obstructions across channel width, can attach with the bedform during its formation to cause floods. To study the impact of the horizontal obstruction in rough bed flow, Devi et al. [4,5] have run a series of experiments by bedmounted cylinder to investigate their flow velocity [4] and turbulence [5]. Using an acoustic Doppler velocimetry (ADV) measurement approach, Devi et al. [4] concentrated on comparison between flow properties impacted by sand and gravel-formed beds, while Devi et al. [5] considered the turbulence of flow above sand bed by high-order bursting analysis. The findings by [4,5] are crucial for consolidating the knowledge of turbulence field induced by the horizontally laying cylindrical obstacle and predicting its actual flow characteristic over a rough bed.

> Tailing dam has been studied by Satyanaga et al. [6], where its sediment tailings have been investigated by incorporating the unsaturated solid mechanic approach. In their study, the soil consolidation process was illustrated to observe the stability of sediment within the dam. The experiment together with numerical analysis proposed within Satyanaga et al.'s study is particularly crucial to understand and manage the operation of the tailing dam. To better understand the dynamics of dredging and its impact on sediment transport within the natural river/watercourse environment, Zikra et al. [7] has studied a case at Nagan Raya Port of Indonesia. In their work, the numerical modelling and field study have

**Citation:** Pu, J.H. Environmental Hydraulics, Turbulence and Sediment Transport. *Fluids* **2022**, *7*, 48.https://doi.org/10.3390/ fluids7020048

Received: 19 January 2022 Accepted: 21 January 2022 Published: 23 January 2022

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been co-utilised, where the results showed a severe impact of dredging towards negatively promoting the sediment transport surrounding the port. The study by Zikra et al. [7] presented useful guidelines not only to the local Nagan Raya Port, but also to portA with similar natural environments.

In supporting structures above the water, various stability research has been performed for many common water-based structures. In the investigation by Bento et al. [8], the flow field around the bridge pier's scour has been studied. The oblong bridge piers have been concentrated in their study, where the proposed experimental results can explore the scour development pattern and hence is useful for the stability study of the bridge's structure. Besides rigid structures like bridges, the floating structures with high degrees of flexibility are also popularly used in water-based projects, e.g, as petroleum drilling platforms. Cui et al. [9] studied the hydrodynamic moment of such flexible structure using 121 sets of detailed experiments. Their results can shed the light on the relative industry in terms of the structural stability and durability subject to constant hydrodynamic loading.

Finally, it is also important to recognise the effort by anonymous reviewers to the abovementioned articles. Without their contributions, this Special Issue would not be possible.

**Funding:** This research received no external funding.

**Acknowledgments:** Throughout the editing of the whole Special Issue and the writing of this Editorial article, the author has been greatly inspired and supported by his family members, Aigul, Jasmin and Jeanette. Without their tireless supports, all these will not be possible.

**Conflicts of Interest:** The author declares no conflict of interest.
