Role of vegetation on attenuation of forces due to cnoidal waves on structures

Date: 19.11.2020; UTC Time: 9:00 AM- 10:00 AM

The tsunami has added a new dimension for the role of vegetation in minimizing the forces on structures in the coastal environment. In the present work, an experimental study has been conducted on the understanding of the variation of forces on structures fronted by vegetation. Slender flexible cylindrical members that represent plantation have been adopted for the tests. The experiments have been conducted for different G/B ratios of 0, 0.5, 1 and 1.5. (Where G is the distance between front face of vegetation/ green belt and the sea side face of the building of width B). Experiments were repeated for three widths of Green belts (BG) and in each of the BG two different diameters were used. The forces on structure were measured in the presence and absence of green belt. The measured results have been compared with existing results available in literature. Cnoidal waves with Ursell parameter ranging between 18 and 700 were employed for the experiments. The different non-dimensional vegetal and flow parameters have been identified. The variation of non-dimensionalised force over the slope in the presence and absence of vegetation as a function of the Ursell parameter, Relative rigidity and reduced velocity for different dimensionless SP/D of the green belt (where SP is the spacing between the stems and D its diameter ) clearly indicates that there is significant reduction in the force. Prior to the experiments with the green belt, tests were carried out on the force measurements of waves over a plane slope and was compared with existing results for the purpose of validation. In this talk, the experimental set-up, procedure and analysis and the results will be discussed.

It has been found that,

1. The non-dimensional Forces on the structure increases by about 80 %, when the distance G between the structure and the Green Belt is in the range of 0.5B to 1.5B.

2. The most favorable location for the Structure is adjacent to the Green Belt (G=0B) or away from the Green Belt by more than 2B. For this configuration the forces can be reduced by a maximum of 90% and to a minimum of 50%.