Analysis of lock-exchange gravity currents over smooth and rough beds

Abstract

Gravity currents produced by full-depth lock-release of saline water into a fresh water tank are studied focusing on the influence of the initial density of the saline mixture in the lock and the bed roughness on gravity current kinematics. Temporal evolution of the current front position and front velocity are analysed and related to different phases of the current. Time–space evolution of current depth-averaged density and current height are assessed as well. Roughness of the channel bed plays an important role in the current kinematics, particularly in decreasing the front velocity due to extra drag at the bed. The analysis of Froude numbers, estimated with the initial and local reduced gravity and established with different length scales of the current, allow for the definition of the important variables and current dynamics of each phase of the current development.

Keywords:

• Bed roughness
• density currents
• density evaluation
• image analysis technique
• lock-exchange experiments

Acknowledgements

This research was supported by the Portuguese Foundation for Science and Technology (FCT), through the research project PTDC/ECM/099752/2008, and the research grant SFRH/BD/48705/2008. Acknowledgements are due to Alexandre Sousa for help in data interpretation. The authors would like to thank the reviewers for helping to improve the content of the manuscript.