Gravity currents from a dambreak in a rotating channel
View/Open
Date
20050726Author
Helfrich, Karl R.
Mullarney, Julia C.
Metadata
Show full item recordCitable URI
http://hdl.handle.net/1912/149As published
http://dx.doi.org/10.1017/S0022112005004544DOI
10.1017/S0022112005004544Keyword
Gravity current; Dambreak problemAbstract
The generation of a gravity current by the release of a semiinfinite region of buoyant fluid of depth $H$ overlying a deeper, denser and quiescent lower layer in a rotating channel of width $w$ is considered. Previous studies have focused on the characteristics of the gravity current head region and produced relations for the gravity current speed $c_{b}$ and width $w_b$ as a functions of the local current depth along the wall $h_b$, reduced gravity $g^\prime$, and Coriolis frequency $f$. Here, the dambreak problem is solved analytically by the method of characteristics assuming reducedgravity flow, uniform potential vorticity and a semigeostrophic balance. The solution makes use of a local gravity current speed relation $c_{b} \,{=}\, c_b(h_b,\ldots)$ and a continuity constraint at the head to close the problem. The initial value solution links the local gravity current properties to the initiating dambreak conditions. The flow downstream of the dam consists of a rarefaction joined to a uniform gravity current with width $w_b$ (${\le}\, w$) and depth on the righthand wall of $h_b$, terminated at the head moving at speed $c_b$. The solution gives $h_b$, $c_b$, $w_b$ and the transport of the boundary current as functions of $w/L_R$, where $L_R \,{=}\, \sqrt{g^\prime H}/f$ is the deformation radius. The semigeostrophic solution compares favourably with numerical solutions of a singlelayer shallowwater model that internally develops a leading bore. Existing laboratory experiments are reanalysed and some new experiments are undertaken. Comparisons are also made with a threedimensional shallowwater model. These show that lateral boundary friction is the primary reason for differences between the experiments and the semigeostrophic theory. The wall noslip condition is identified as the primary cause of the experimentally observed decrease in gravity current speed with time. A model for the viscous decay is developed and shown to agree with both experimental and numerical model data.
Description
Author Posting. © Cambridge University Press, 2005. This article is posted here by permission of
Cambridge University Press for personal use, not for redistribution. The definitive version was published
in Journal of Fluid Mechanics 536 (2005): 253283, doi:10.1017/S0022112005004544.
Collections
Related items
Showing items related by title, author, creator and subject.

Measurements and models of finestructure, internal gravity waves and wave breaking in the deep ocean
Eriksen, Charles C. (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 197609)Measurements of horizontal and vertical current by propeller cluster current meters and temperature by thermistors mounted on a rigid array 8 m high and 20 m long moored in the oceanic main thermocline near Bermuda are ... 
Density currents in the Chicago River : characterization, effects on water quality, and potential sources
Jackson, P. Ryan; Garcia, Carlos M.; Oberg, Kevin A.; Johnson, Kevin K.; Garcia, Marcelo H. (200803)Bidirectional flows in a river system can occur under stratified flow conditions and in addition to creating significant errors in discharge estimates, the upstream propagating currents are capable of transporting contaminants ... 
Wave breaking turbulence at the offshore front of the Columbia River Plume
Thomson, James M.; HornerDevine, Alex R.; Zippel, Seth; Rusch, Curtis; Geyer, W. Rockwell (John Wiley & Sons, 20141219)Observations at the Columbia River plume show that wave breaking is an important source of turbulence at the offshore front, which may contribute to plume mixing. The lateral gradient of current associated with the plume ...