Abstract
Dams are important for flood mitigation, water supply, and hydroelectricity. Every dam has a water conveyance structure, such as a spillway, to safely release extreme floods when needed. The flows down spillways are often self-aerated and spillway design has typically been investigated in laboratory experiments, which is due to limitations in suitable full scale flow measurement instrumentation and safety considerations. Prototype measurements of aerated flows are urgently needed to quantify potential scale effects and to provide missing validation data for design guidelines and numerical simulations. Herein, an image-based analysis of free-surface flows on a stepped spillway was conducted from a top-view perspective at laboratory scale (fixed camera installation) and prototype scale (drone footage). The drone videos were obtained from citizen science data. Analyses allowed to remotely estimate the location of the inception point of free-surface aeration, air–water surface velocities, and their fluctuations, as well as the residual energy at the downstream end of the chute. The laboratory results were successfully validated against intrusive phase-detection probe data, while the prototype observations provided proof of concept at full scale. This study highlights the feasibility of image-based measurements at prototype spillways. It demonstrates how citizen science data can be used to advance our understanding of real world air–water flow processes and lays the foundations for the remote collection of long-missing prototype data.
Highlights
Reservoir dams represent a key part of water infrastructure and any failure or collapse would be catastrophic, causing rapid and unexpected flooding, which may result in destruction of property and loss of life [1]
Intense research has been carried out to understand the process of aeration and how it affects the hydraulics of spillway chutes
This study presents a proof of concept to remotely estimate air–water surface velocities and associated parameters in aerated flows down laboratory and prototype chutes
Summary
Reservoir dams represent a key part of water infrastructure and any failure or collapse would be catastrophic, causing rapid and unexpected flooding, which may result in destruction of property and loss of life [1]. Every dam is equipped with a flood release structure, often a spillway, which is designed to enable safe conveyance of flood waters (Figure 1a,b). A spillway must be soundly designed for the full range of potential flow conditions, accounting for flow aeration [2,3]. Flow aeration is often described as “white waters” and entrained air leads to flow bulking and drag reduction, which is associated with reduced energy dissipation [4,5], having a significant influence on design and operation of hydraulic structures. The region just downstream of the weir-crest is non-aerated, while the flows become aerated at the so-called inception point of free-surface aeration (Figure 1b). The aerated region is characterized by a range of air concentrations c within the air–water column, representing bubbly flow (c < 0.3), intermediate flow
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