Hydraulics of Plane Plunge Pool Scour

Abstract

Plunge pool scour involves a significant risk with trajectory spillways because of structural undermining at a dam foot or destabilization of adjacent valley slopes. An experimental program towards the understanding of plane plunge pool scour of a completely disintegrated rock surface was conducted, in which the following items received attention: jet shape, jet velocity, jet air content, tailwater elevation, granulometry, upstream flow to the scour hole, and the end scour profile in terms of the basic scour features. These effects were experimentally investigated based on a systematic variation of the governing scour parameters. The results of this paper allow answering questions that have so far not been addressed. Design equations were proposed to sketch the main tendency of the data sets. The significant effect of the densimetric particle Froude number was substantiated. This research may be used to estimate the prominent scour features for nearly two-dimensional jet arrangements involving a pre-aerated high-speed flow.

Morphological dynamics of an englacial channel

“…Cave size will be influenced by discharge, flow velocity and step-riser height that, combined, control the degree of flow detachment and jet breakup and impact point. Dimensions of these caves are likely mediated by energy dissipation and ice creep closure; this quasi-equilibrium form may be analogous to that suggested in flume studies and theoretical considerations for bedrock rivers (Mason and Arumugam, 1985;Stein et al, 1993), where jet impact angle, jet velocity, and the tailwater depth are influential (Pagliara and Hager, 2006). A combination of a partly bed-supported and partly ballistic jet at a type 1B knickpoint may lead to higher recession rates in the upper part of the riser face, allowing transition towards type 1A morphology.…”

Plane plunge pool scour with protection structures

“…It has to be noted that the scour profile measurements for 1 and 5 minutes from the beginning of the experiment are not representative of an ''instantaneous'' condition, since the measurement time is about 1 minute for a single profile. All the tests were conducted in both unsubmerged jet and black-water (corresponding to no air presence in jet) conditions, although as stated by Pagliara et al (2006) for black-water flows, scour depths are practically the same for both submerged and unsubmerged jets. The distance between the pipe and the water surface was kept constant and equal to about 2 times the pipe diameter D. Thus no jet curvature can occur and the characteristics of the impinging jet on the water surface can be considered the same as the ones present at the pipe outlet.…”

“…Mason (2002), Canepa and Hager (2003), Dey and Sarkar (2006a) and Dey and Sarkar (2006b) also gave a considerable contribution to find out the main hydraulic and geometrical parameters which govern the scour phenomenon. More recently, Pagliara et al (2006) studied the hydraulics of plane plunge pool scour in clear water conditions and proposed some useful relationships to find out the maximum scour depth without any protection work in the stilling basin. When a protection structure is introduced, the whole scour mechanism changes depending on the type and the location of the structure.…”

Influence of aeration and initial water thickness on axial velocity attenuation of jet flows

“…Bohrer et al (1998) documented velocity decay of free falling rectangular jet in a plunge pool. Due to the difficulties in performing measurements inside the flow, research in this area has concentrated on the resulting outcome of the aerated jet flows, i.e., the impact pressure and the scour in the pool bottom (Chatterjee et al, 1994;Sarkar and Dey, 2004;Pagliara et al, 2005). Regarding jet aeration, the effects of the amount of air on the scouring are much more complicated and the interaction between air-water and riverbed material must be considered, as well as the air entrainment, the geological and geotechnical characteristics of the riverbed.…”