Showing papers by "Vallam Sundar published in 2021"

Baseline Study on Microplastics in Indian Rivers under Different Anthropogenic Influences

Abstract: Microplastic particles are found in environmental compartments all over the world and receive a great deal of attention, especially in the aquatic environment. Currently, a particularly high input of microplastics via Asian rivers is assumed, but so far, there are hardly any data through field measurements. Three rivers in South India were considered for this purpose to focus on their microplastic load. The emphasis was on the comparison of microplastic concentrations in urban and rural rivers. While two rivers in the megacity Chennai (Tamil Nadu) were found to have an average microplastic concentration of 0.4 microplastic particles/L, a rural river near Munnar (Kerala) had an average concentration of 0.2 microplastic particles/L. Rough estimates of annual microplastic discharge from the Adyar River (Chennai) into the Bay of Bengal are found to be as high as 11.6 trillion microplastic particles. This study should be one of the first baseline studies for microplastic loads in South Indian streams and should be complemented with further environmental sampling before, during and after the monsoon season to get more detailed information on the storage and transportation of fluvial microplastics under different weather conditions.

Hydrodynamic performance characteristics of an oscillating water column device integrated with a pile breakwater

Abstract: The hydrodynamic performance characteristics of an oscillating water column (OWC) device mounted on a pile-supported breakwater (OWC-PSB) exposed to action of regular and random waves is investigated. The results are compared with that of a vertical wall type pile-supported breakwater (VW-PSB). The experiments were carried out in a wave flume in a constant water depth of 0.95 m covering intermediate to deepwater conditions. The wave energy transmission past both models is found to be similar under deepwater conditions, and marginally less for OWC-PSB in intermediate water depths. The OWC-PSB model exhibited less wave reflection for most of the tests. Since a part of incident wave energy is converted to water column oscillations inside the OWC chamber, the energy dissipation co-efficient for OWC-PSB is more than that for VW-PSB. The wave amplification factor for the OWC device is higher for long waves; however, the hydrodynamic efficiency is higher for high-frequency waves with the efficiency being a maximum close to 50% under deepwater conditions.

Three-dimensional direct numerical simulation of flow induced by an oscillating sphere close to a plane boundary

Abstract: The dynamic interaction of submerged spherical structures with ocean waves alters the local flow field and is responsible for the movement of sediments over the seabed, which would have detrimental effects on the ecosystems. The present research aims to gain insight into the effect of a plane boundary on the vorticity dynamics and shear modifications on the plane boundary induced by the flow due to an oscillating sphere. The flow field around an oscillating sphere close to a plane boundary is investigated numerically by three-dimensional direct numerical simulation of the Navier–Stokes equations. The sphere oscillates perpendicular to the plane boundary modeling the seabed. The flow structure, resulting mean and fluctuating shear stress distribution on the plane boundary, and the Lagrangian particle transport are investigated as a function of the sphere oscillation amplitude, Reynolds number, and the distance of the sphere from the plane boundary. The systematic correlations for the variation of maximum shear stress on the plane boundary are estimated from scaling parameters. The time-mean results are then linked to the Lagrangian particle transport where it is observed that the Lagrangian path lines track the mean streamlines closely. Further, the particles at the stagnation zone cease drifting and oscillate about a constant mean position. The practical significance of this result is that a ring of zero mean shear on the seabed is found toward where particles congregate. This provides a guide for the optimum location for the mooring anchors, minimizing the risk of anchor scour or undermining.

Hydrodynamic characteristics of vertical and quadrant face pile supported breakwater under oblique waves

Abstract: This paper presents the results from a comprehensive experimental study on the Quadrant Face Pile Supported Breakwater (QPSB) in two different water depths exposed to three different oblique wave a...

Shoreline changes due to construction of groyne field in north of Chennai Port, India.

Abstract: Chennai Port (13.099872° N, 80.297407° E), located along the southeast coast of India, has been a hub for maritime trade since the fifteenth century. An artificial harbour was initially constructed in 1881 which underwent numerous expansions in the following years. The breakwaters of the harbour intercepted the heavy sediment-laden littoral drift along the coast, resulting in the formation of the world's second-longest urban beach south of the port, i.e. on its up-drift side. Meanwhile, the coast north of the port, i.e. the down-drift side, experienced intense erosion due to a lack of sediment supply and forces induced on the coast due to waves and currents. The shoreline change study in this paper investigates a shoreline stretch of about 6 km (protected by transitional groynes), north of Chennai Port by dividing it into three segments. The rate of shoreline changes over a period of about 12 years across three different segments was assessed using statistical parameters by employing remote sensing techniques complemented with geographical information system (GIS) and digital shoreline analysis system (DSAS) tool. It is inferred that the coast has witnessed accretion and sizable growth in beach width has been observed post the construction of groyne field.

Sustainable hard and soft measures for coastal protection – Case studies along the Indian Coast

Abstract: Any stretch of a coastline warrants protection measure when it experiences an erosion rate beyond a threshold value, and when the seasonal littoral drift changes fail to restore equilibrium. The ca...

Geo-technical Stability and Sensitivity Analysis of Geo-synthetic Seawall at Pallana Beach, Kerala, India

Abstract: The various geo-synthetic components such as geo-tubes, geo-bags, geo-mattresses, geo-containers, geo-grids, geo-cells find extensive applications in coastal engineering practice. It is more sought after due to the ease of construction, quick implementation and reduced cost as the supply of natural rocks is eluded. Innovative geo-synthetic materials of numerous units were compounded to form a sea wall cross section, to be constructed at Pallana coast (9° 17′ 55.19″ N and 76° 23′ 18.55″) of Allepey, Kerala, to prevent wave run up during high tide level. The Pallana beach is also characterized with poor soil subgrade properties and hence the proposal to construct a geo-synthetic seawall in contrast to the conventional measures. The cross section is designed to ensure stability against overturning, sliding, overtopping and scour protection. The major concerns such as UV radiation, stability against wave action, settlement of the structure and protection against scour are to be addressed prior to the implementation of the design on site. The objective of the paper is to arrive at the significant geo-technical parameters responsible for the geo-technical stability of the structure over time. The pore-water pressures beneath the structure, rapid drawdown, transient stability and sensitivity analysis are computed for the above said structure using GeoStudio software application, which employs finite element method. A visualization of the geo-technical performance can be arrived that aids to verify the design parameters adopted.

Studies on Locating Sediment Trap for Reducing Dredging in Jellingham Navigational Fairway, Kolkata

Abstract: Formation of shoals in an estuarine environment creates significant problems such as reduction in depth in navigational channels, decreased discharges and degradation of water quality. One of the widely used solutions to reduce sedimentation is the implementation of a sediment trap by creating a trench or a pit in the submerged bottom at specific locations. A sediment trap is defined as a section of the estuarine bed deepened to a depth greater than its surroundings. The lower velocity allows sediments to deposit in the trap rather than move past over it. Implementation of a silt trap at specific locations in a highly dynamic domain like Hooghly estuary helps to optimize the dredge quantity or the maintenance dredging can be localized to a specific location (the trap) rather over a wide submerged area. This study involves optimization of the location and shape of a silt trap near the Haldi-Hooghly confluence point, West Bengal, India. The trap was designed to reduce the dredging quantity in the downstream Jellingham channel which is a part of the navigational channel en route to Haldia Dock Complex in the Hooghly estuary. Based on a comprehensive numerical study, an option of irregular polygon shaped silt trap of a surface area of 250,000 m2 positioned in such a way to trap the sediments from both the Hooghly and the Haldi rivers near the Haldia anchorage was finalized which was found to perform efficiently in reducing the dredge quantity in the Jellingham channel. The details of the study are reported in this paper.

Stability of Groynes Built Using Geo Systems

Abstract: In general, the groyne sections are made of rubble stones of different sizes. To conserve the ecosystem and also due to the scarcity of natural rocks around certain locations, the reliance on these hard materials for the construction of groyne sections becomes questionable forcing us to look for alternate eco-friendly soft materials, for example, geo systems. In order to evaluate the feasibility and advantages of geo systems for groyne construction and to test their hydrodynamic stability, the core section of rubble stones was replaced by geo-bags filled with sand. The objective of this study is to assess the wave transmission, hydrodynamic stability and wave overtopping of a groyne section with a geo-bags filled core section through physical model studies. The tests were conducted in a wave flume in Department of Ocean Engineering, Indian Institute of Technology Madras, India. A model scale of 1:15 is adopted based on Froude’s scaling law and dimensional limitations of the testing facility. The aforementioned cross sections were tested simultaneously in a wave flume that was partitioned longitudinally. The transmission and hydrodynamic stability of both the sections have been analysed by subjecting the corresponding sections to the action of random waves defined by JONSWAP spectrum through a well-controlled experimental programme. The details of test set-up, testing facility, parameters of model, test procedure, analysis of results and discussion will be reported in this chapter.

Design of a Minor Fishing Harbor in India with Special Reference to Training of the Mouth of River Chapora

Abstract: Most of the fishing harbors along the Indian coast are located within the tidal inlets, barring a few on the open coast. Fishing harbor on an open coast needs protection in the form of breakwaters or training walls for providing tranquility conditions and safe vessel maneuvering and landing facilities. Practically, all inland fishing harbors suffer siltation problems. The studies on the development of a new inland fishing harbor on River Chapora (15° 36′4 6.22″ N and 73° 44′ 51.34″ E) in the state of Goa in India with such problem were carried out, the results of which are reported in this paper.