Performance of flexible emergent vegetation in staggered configuration as a mitigation measure for extreme coastal disasters

The performance characteristics of emergent greenbelt vegetation has received considerable attention in the recent years, post-Great Indian Ocean Tsunami (26 December 2004). In the present work, a comprehensive laboratory study on the hydraulic resistance characteristics due to a group of slender cylindrical members representing flexible plantation has been carried out in a laboratory open channel. The model stem groups comprised of individual members of different sizes and concentrations in staggered configuration. The sizes and concentrations were chosen in such a way that they would fall into the practical ranges of vegetations in coastal forestry. The results indicate that the flow resistance varies with stem concentration, stem diameter and elastic properties of the individual members and the flow velocity. Based on the results, the Darcy friction factor, f, for various flow and vegetative parameters was derived. A new empirical equation is proposed for evaluating f for partially submerged vegetation in staggered configuration for a wide range of depths of flow in relation to un-deflected plant heights. It is expected that the f thus determined will be useful in modelling the shallow flows using shallow water equations. © 2012 Springer Science+Business Media B.V.