Abstract
A positive surge is an unsteady open channel flow motion characterized by an increase of flow depth. In previous experimental studies, a positive surge was typically induced by either a sudden increase of discharge in a channel or by the rapid closure of a downstream sluice gate, thus leading to a steep initial profile. However, in many instances, the evolution of a positive surge is of a progressive manner (e.g., in the downstream navigation canal during the emptying operation of lock chambers). In the present work, the inception and development of a positive surge induced by a progressive increase of discharge was investigated in a rectangular channel with a smooth bed. Both undular and breaking surges were studied. The results demonstrate that the maximum wave height at the first wave crest of an undular surge is in very close agreement with the McCowan theory. Additionally, the wave amplitude essentially shows a linearly increasing trend with an increasing surge Froude number up to Fr0 = 1.26 to 1.28, whereas it tends to suggest a power law reduction for larger surge Froude numbers. Moreover, the dispersion of undular surges is consistent with the linear wave theory only for surge Froude numbers close to unity. Overall, the present study demonstrates the unique features of positive surges induced by a progressive increase of discharge.
Highlights
A positive surge is an unsteady open channel flow motion characterized by an increase of flow depth [1]
The free-surface properties of a positive surge induced by the progressive opening of an
The free-surface properties of a positive surge induced by the channel progressive an upstream plate gate were investigated experimentally in a rectangular with opening a smoothofbed
Summary
A positive surge is an unsteady open channel flow motion characterized by an increase of flow depth [1]. Positive surges are widely observed in man-made and natural channels. They may be induced by the emptying of lock chambers during lock operations [2] or by sluice gates installed along water supply canals for irrigation and power purposes [3]. The passage of undular and breaking surges is associated with significant variations in hydrodynamics (i.e., flow velocity, water level and Reynolds stresses), and they can be expected to affect the mixing and advection processes of sediments in channels [4,5]. In the case of navigation channels, these surges potentially influence tow’s maneuverability, thereby affecting the navigation safety and functional efficiency of locks [6]
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