Attenuation of Wave Energy Due to Mangrove Vegetation off Mumbai, India

Abstract

Coastal regions of India are prone to sea level rise, cyclones, storm surges, and human-induced activities, resulting in flood, erosion, and inundation, and some of these impacts could be attributed to climate change. Mangroves play a very protective role against some of these coastal hazards. The primary aim of the study was to estimate wave energy attenuation by mangrove vegetation using modeling, and to validate the model results with measurements conducted off Mumbai coast, where a mangrove forest is present. Wave measurements were carried out from 5–8 August 2015 at three locations in a transect normal to the coast using surface-mounted pressure-level sensors in spring tide conditions. The measured data presented wave height attenuation of the order of 52%. Model set-up and sensitivity analyses were conducted to understand the model performance with respect to vegetation parameters. It was observed that wave attenuation increases with an increase in drag coefficient, vegetation density, and stem diameter. For a typical set-up in the Mumbai coastal region having a vegetation density of 0.175 per m2, stem diameter of 0.3 m, and drag coefficient varying from 0.4 to 1.5, the model reproduced attenuation ranging from 49% to 55%, which matches reasonably well with the measured data. Spectral analysis performed for the cases with and without vegetation very clearly portrays energy dissipation in the vegetation area. This study also highlights the importance of climate change and mangrove vegetation.

Mangroves As Coastal Bio-Shield: A Review of Mangroves Performance in Wave Attenuation

“…Thus, accounting the various parameters taken, the reduction performance in the following cases might not be comparable among cases, but the dissipation function on several wave conditions is still proven. [69,74]. As previously explained, bottom friction is the driving factor influencing the wave reduction, along with the vegetation drag force.…”

Wave Climate Variability and Occurrence of Mudbanks Along the Southwest Coast of India

“…Mudbanks prevail in semi-circular shape and extend up to 8-10 km offshore in water depth up to 15 m and 3-4 km alongshore. As was shown mud dominated bottom can damp the waves (Rajesh Kumar et al, 2008;Parvathy and Bhaskaran, 2019) and this effect comparable with wave attenuation due to the vegetation (Samiksha et al, 2019). Samiksha et al (2017) studied the wave attenuation due to the MBs using measurements and modeling and found that 65-70% of waves dampened in the MBs area.…”