Abstract
Over the last two decades, interest in the free-surface behaviour of gravity-driven shallow turbulent flows has increased considerably. It is believed that observation of free-surface behaviour can provide useful information about the hydrodynamic characteristics of the flow and enable remote retrieval of these characteristics to non-invasively and rapidly monitor river flows. At the current state the literature presents scattered knowledge and also exhibits non-uniformity in the terminology used. This paper is a review of the state-of-art of this area of research and was created with two objectives: to gather the information relevant to understand the linkages between the free-surface behaviour and underpinning hydrodynamic processes while using a uniform terminology, and to analyse the gaps in our knowledge of this critical topic.
Highlights
There are many factors that govern the dynamics of streams, rivers and other open channel flows
This paper is a review of the state-of-art of this area of research and was created with two objectives: to gather the information relevant to understand the linkages between the free-surface behaviour and underpinning hydrodynamic processes while using a uniform terminology, and to analyse the gaps in our knowledge of this critical topic
When the free-surface velocity is slower than the minimum phase velocity for gravity-capillary waves in still water, cmin = 0.23 m s−1, the dominant pattern is formed by waves induced by turbulence through the forcing non-resonant growth proposed by Teixeira and Belcher (2006)
Summary
There are many factors that govern the dynamics of streams, rivers and other open channel flows. The free-surface interface represents the dynamic upper boundary of an open channel flow system, it seems reasonable to suggest that the free surface is influenced by the same parameters. The existing literature is approached from an application-based perspective, focusing on studies that provide directly usable information to link free-surface observations with flow conditions. For this reason, more theoretical works about the physical details of the process beyond what is measurable in realistic field conditions, or numerical studies focused on simulation approaches rather than on observable results, are not discussed in detail. Studies; Section 3 describes the main mechanisms that govern free-surface dynamics; Section 4 presents a review of the most influential studies of free-surface shallow turbulent flows which have attempted to establish relationships between the bulk flow parameters and the free-surface pattern; key findings are discussed in Section 5; and in Section 6 conclusions are derived and gaps in the knowledge are summarized along with recommendations as to how these may be addressed
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