Role of tree crown height for effective mitigation capability of inland coastal forest considering the flow structures and scour phenomena

Abstract

This research investigated the relationship of tree crown height with the trunk part under the mobile bed condition for the proper management of inland coastal forests. A series of flume experiments under the quasi-steady flow conditions were performed while varying different parameters like change in crown heights from the ground (highest Hct = 0.7, medium Hct = 0.5, and lowest Hct = 0.3; where Hct = hc/ht: Hct is the non-dimensional parameter, hc is the crown height from ground and ht is the tree height), forest thicknesses in the streamwise direction i.e. L and L/2 (where L is the forest length), and initial Froude number conditions (Fr) ranging from 0.668 to 0.732. The outcomes demonstrated that the flow structures are strongly influenced by the lowest crown height i.e. Hct = 0.3 causing the maximum flow energy reduction i.e. 40-43%. On the contrary, the scour produced around the forest due to the high impact force of overflowing water became excessive that can significantly damage the coastal forest defense system. The optimum results in the form of significant energy reduction of the approaching current and minimum vulnerability (permissible scouring) of the defense system have been observed to be associated with the medium crown height i.e. Hct = 0.5 and largest possible forest thickness.