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Laboratory investigations on the effect of fragmentation and heterogeneity of coastal vegetation in wave height attenuation
(Springer, 2019) Shirlal, K.G.; John, B.M.; Rao, S.
It has long been known that “bio-shields” do function as a sustainable solution for preserving our coasts. The presence of gaps in the “bio-shield”, that is, the forest cover, referred to as patchiness, is a common phenomenon in natural habitats. Various anthropogenic and natural causes can result in such gaps in coastal forests. This paper presents the results of a physical model investigation carried out with a fragmented heterogeneous vegetation model in a wave flume 50 m long, 0.71 m wide and 1.1 m deep. The heterogeneous meadow is modelled as a combined body of artificial submerged seagrass, rigid vegetation and emergent vegetation. To study the effect of fragmentation in vegetation, transverse gaps of varying widths are introduced in the heterogeneous model. The material used for modelling is polyethylene and nylon. The test runs were carried out with monochromatic waves of heights ranging from 0.08 to 0.16 m in water depths of 0.40 and 0.45 m, and wave periods 1.8 and 2 s. The wave height measurements at different locations within the vegetated meadow exhibit an exponential decay of wave heights. The presence of gaps in vegetation does not have a significant effect on wave height reduction. However, the experimental study revealed that heterogeneous vegetation showed a great promise leading to considerable wave attenuation, thus offering a good level of protection to life and property on the leeside. © Springer Nature Singapore Pte Ltd. 2019.
Effect of artificial vegetation on wave attenuation - An experimental investigation
(Elsevier Ltd, 2015) John, B.M.; Shirlal, K.G.; Rao, S.
In the wake of threats posed by rising sea levels and increasing severity of storms, the use of soft measures in coastal protection is acquiring an ever increasing importance. Coastal vegetation acts as a complex interface ecosystem between human communities and the sea and provides important ecosystem services by protecting these communities from coastal hazards, providing critical habitat for fishes and marine invertebrates and primary food source for animals like sea turtles. This paper tries to bring out the effect of simulated vegetation on wave attenuation through an experimental study. The tests were carried out with submerged artificial seagrass and artificial rigid vegetation in a 50 m long wave flume. For wave heights ranging from 0.08 m to 0.16 m at an interval of 0.02 m and wave periods 1.8 s and 2 s in water depths of 0.40 m and 0.45 m, measurements of wave heights at locations along the vegetation were observed. Â© 2015 The Authors. Published by Elsevier Ltd.
An experimental investigation on the hydraulic performance of suspended perforated hollow cylinders in a single row with a relative clear spacing of 0.15 between pipes was conducted in a two- dimensional wave flume. The influence of relative depth of submergence, incident wave steepness, size of pipes, size of perforations, percentage of perforations and water depth on wave attenuation has been investigated. From the investigation it was found that, as the depth of submergence increases transmission coefficient decreases. But beyond 50% of depth of submergence decrease in transmission is negligible. Transmission decreases as incident wave steepness increases. Forperforated pipes, size of the pipe has marginal effect on transmitted wave characteristics for the relative clear spacing considered. Perforated pipes with 25% of perforations are found to attenuate about 10% to 14% more wave energy than non-perforated pipes. Size of perforations does not have much effect on transmission for the same area of perforations. © 2001 Taylor & Francis Group, LLC.
(Laboratory investigation on wave transmission through suspended perforated pipes) Rao, S.; Rao, N.B.S.
2001
Tandem Breakwater consists of a submerged reef breakwater constructed at some distance in front of a conventional non-overtopping rubble mound breakwater. The submerged reef breakwater breaks the high waves and the stilling basin between two breakwaters attenuates them. Hence, smaller waves approach the non-overtopping rubble mound breakwater and break on it. Therefore, the non-overtopping rubble mound breakwater may be designed for smaller waves, resulting in relatively lighter armour stones. In the model studies, it has been found that for a relative breakwater spacing X/d varying from 3.33 to 4.29 between the breakwaters, the damage of a tandem Breakwater is 20% to 60% less as compared with a single breakwater for similar operating criteria. © 2003 Taylor & Francis Group, LLC.
(Laboratory studies on the stability of tandem breakwater) Shirlal, K.G.; Rao, S.
2003
The concept of rubble mound breakwater and submerged reef breakwaters, operating together as a single unit, is called the tandem breakwater. The effect of the submerged reef breakwater on the stability of non-overtopping rubble mound breakwater on its leeside was investigated in the present study, The tandem breakwater was tested for two spacings between the breakwaters, ie,for 1 m and 2,5 m. For each of the spacing, the effect of water depth, wave-period and wave height on the stability of tandem breakwater was studied. In the present study, the damage level of tandem breakwater for a relative spacing varying from 2.22 to 7.14 was 10% to 40% less compared to that of a single breakwater designed to meet the same operating criteria.
(Stability of tandem breakwater) Shirlal, K.G.; Rao, S.; Prasad, S.K.M.
2003
Laboratory investigation on horizontal and vertical plate breakwaters
(2010) Rao, S.; Shirlal, K.G.; Prashanth, S.; Varghese, R.V.
Submerged breakwaters are commonly used for coastal protection on many eroding coasts. Plates are proved to induce wave breaking and dissipate wave energy. These have the advantages of low interference with current and sediment transport while saving substantial quantity of material. They permit exchange of surface and subsurface water and living organisms and hence, suitable for ecologically sensitive region. This paper explains the physical model studies to evaluate the transmission coefficients of a rigid submerged horizontal and vertical plate. It is found that the horizontal plate with ds/Hi < 1.0 is effective to bring the values of Kt below 0.6 when d/L > 0.22. Vertical plate is effective for the entire range of d/L for ds/Hi = 0. © 2010 Taylor & Francis Group, LLC.
Wave steepness and relative width: Influence on transmission coefficient of horizontal interlaced, multilayered, moored floating pipe breakwater with five layers
(2011) Rajappa, S.; Hegde, A.V.; Rao, S.; Channegowda, V.
This paper presents the results of a series of physical model scale experiments conducted to determine the transmission characteristics of a horizontal interlaced, multilayered, moored floating pipe breakwater. The studies are conducted on physical breakwater models having five layers of PVC pipes. The wave steepness (H i/gT 2, where H i is incident wave height, g is acceleration due to gravity, and T is time period) was varied between 0.063 and 0.849, relative width (W/L, where W is width of breakwater and L is the wavelength) was varied between 0.4 and 2.65, and relative spacing (S/D, where S is horizontal centre to centre spacing of pipes and D is the diameter of pipes) was set equal to 2. The transmitted wave height is measured, and the gathered data are analyzed by plotting nondimensional graphs depicting the variation of K t (transmission coefficient) with Hi/gT 2 for values of d/W (d is depth of water) and of K t with W/L for values of H i /d. It is observed that K t decreases as H i /gT 2 increases for the range of d/W between 0.082 and 0.139. It is also observed that K t decreases with an increase in W/L values for the range of H i /d from 0.06 to 0.40. The maximum wave attenuation achieved with the present breakwater configuration is 78%.
Laboratory investigations of wave attenuation by simulated vegetation of varying densities
(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2019) John, B.M.; Shirlal, K.G.; Rao, S.
Coastal communities across the world are facing the need to adapt to rising sea levels, an increase in the frequency of natural hazards like storm surges, cyclones, tsunamis, and an increase in beach erosion. This present-day scenario calls for a sustainable, environment-friendly, and cost efficient solution for coastal protection. Under these circumstances, the role of vegetation in providing ecosystem services to coastal populations is becoming increasingly prominent. This work presents the results of an experimental study carried out with simulated rigid submerged and emergent vegetation meadows of varying plant densities in a wave flume 50 m long, 0.71 m wide and 1.1 m deep. The material used for modeling the vegetation is nylon. The tests are carried out with regular waves for water depths of 0.40 and 0.45 m, and wave periods 1.4–2 s at an interval of 0.2 s. Five different wave heights ranging from 0.08 to 0.16 m at an interval of 0.02 m are generated. Measurements of wave heights at different locations indicate an exponential decay in wave height along the vegetation meadow which leads to wave attenuation and confirms that vegetation can be a viable option for coastal protection. © 2017, © 2017 Indian Society for Hydraulics.
Hydrodynamic performance of floating kelp farms: Wave attenuation and coastal protection potential
(Elsevier Ltd, 2025) Surakshitha; Rao, M.; Rao, S.
Ecologically rich coastal zone play a crucial role in supporting both biodiversity and the economy. “Soft solutions” for coastal protection, such as vegetated breakwaters and artificial reefs, harness natural features to mitigate coastal erosion. Among these, flexible floating vegetation, such as kelp farms, presents a unique mechanism by altering flow patterns differently than bed-fixed vegetation. This study experimentally investigates the effectiveness of floating kelp farms in dissipating wave energy under monochromatic regular waves. The wave heights ranging from 0.06 m to 0.18 m and periods of 1.6 s–2.8 s is considered. The study examines the effects of two non-dimensional parameters: relative farm width (w/L, 0.1 to 2.5) and relative blade length (l/d, 0.25–1.0), representing the ratios of farm width to wavelength and blade length to water depth, respectively. Under the test conditions investigated, the highest wave dissipation coefficient (Kd ? 0.8) is observed for relative blade lengths of 0.75 and 0.5 at a water depth of 0.45 m. The optimal farm configuration occurred at a relative farm width between 0.3 and 0.4. These findings contribute to a better understanding of the role of kelp farm in wave energy dissipation and highlight its potential as a sustainable alternative for coastal protection. © 2025 Elsevier Ltd

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