Ranganathan Sundaravadivelu

Abstract: Shoreline erosion takes place due to the movement of sand by tides, wave actions, and wave-induced currents. The conventional techniques used for coastal protection such as artificial armor units and rubble mound are costly, and transportation is difficult in remote areas. Moreover, they may not be suitable for poor soil conditions. In this paper, the detailed physical experimental studies were carried out for a geo-tube saline embankment with ten geo-tubes in a four-layer configuration in a wave flume. This soft engineering solution may be particularly viable since the location is remote with poor soil strata. The studies include a scaled model (1:10) of geo-tube embankment with and without gabion boxes to check its possible utilization for coastal protection. The model is tested in the deep wave flume equipped with a piston type wave maker. The embankment is studied for two different water depths of 0.4 m and 0.5 m. The chosen 0.4-m water depth characterizes the high tide condition, while the 0.5-m water depth reproduces the combined high tide and storm surge conditions. The regular wave heights are varied in the range of 2 to 16 cm with a corresponding wave period of 1.5 to 2.2 s. Three probe methods are used to obtain the hydrodynamic parameters, based on which a geo-tube embankment protected with gabion box as armor is designed and constructed along the coast of Pentha (Odisha, India).

Abstract: Chilika lake is the largest lagoon along the east coast of Indian state Odisha, situated between latitude 19° 28′ and 19° 54′ N and longitude 85° 05′ and 85° 38′ E. The place is known for rich biodiversity and is the largest wintering ground of migratory bird and largest population of Irrawaddy dolphin, habited by migratory birds and by a special type of dolphins. The highly productive ecosystem of the lake supports the livelihood for fishermen and also acts as drainage for Mahanadi River Basin. The estuary is very sensitive to the sediment dynamics. The closure of estuary mouth or shifting of Chilika Lake mouths tremendously changes salinity and ecology of the lake system. The east coast of India along this coast is having a net alongshore drift of about 0.7 × 106 m3 annually toward north direction. The inlets of Chilika Lake are under the influence of alongshore sediment transport from the coast. Apart from this, the rivers bring sediments during peak southwest monsoon season. Because of this the inlets are migrating, depending on the season. The details of migration of estuary opening were analyzed using satellite imageries. The analyses of watershed, coastal process, and configuration of estuary are detailed in this paper.

Abstract: ) Corresponding author Abstract: In the last decades the design of stepped spillways regained some interest because of their suitability with new construction methods including gabions. The hydraulic performances of gabion stepped weirs were investigated experimentally in terms of the flow patterns, air-water flow properties and energy dissipation. A laboratory study was conducted in a 26.6° slope (1V:2H) and 0.10 m step height facility with both smooth impervious and gabion steps. The visual observations highlighted the seepage flow through the gabions, inducing a modification of the cavity flow, especially in the skimming flow regime. In skimming flows, higher velocities were measured at the downstream end of the gabion stepped chute, associated with smaller energy dissipation rates and lower friction factors, compared to the smooth impervious stepped chute data. Keywords: Gabion weirs, Stepped spillways, Energy dissipation, Air entrainment, Physical modelling.

Abstract: Critical rainfall for flash flood early warning is a converse result of precipitation-runoff process based on warning discharge threshold for a warning station of interest in a watershed; the key aspects of critical rainfall include rainfall amount and rainfall duration. Using hydrological modeling technique with detailed sub-basin delineation and manual for design precipitation-runoff computation, this study introduces basic concept and methods of analyzing critical rainfall for flash flood early warning. Taking South Branch of Censhui watershed in China as an example, typical critical rainfalls for flash flood dynamic early warning were estimated for 3 warning stations located in the watershed. This research illustrates that detailed watershed characteristics in the context of several warning stations can be modeled in-depth by further delineating the watershed into smaller sub-basins to simulate spatial distribution of various basin parameters. It further confirms that time of concentration of a watershed is an important factor to rainfall duration determination, and the antecedent soil moisture condition of a watershed has significant impact on critical rainfall for same rainfall duration.

Abstract: This article evaluates the impacts of ‘Fani’, a category four cyclone on the shoreline and ecology of the largest brackish water lagoon of Asia, Chilika, on the East Coast of India. The cyclone forced open two New Tidal Inlets (NTI) along the northern shore of the lagoon’s outer channel leading to erosion of the embankments and spits. The average rate of change due to cyclonic storm ‘Fani’ was – 6.12 m while 66.03% of the total transects registered symbol of erosion along the shoreline of Chilika lagoon. Post Fani the information made available on its impact on Chilika was minimal which made us to look into published news articles, online news channels,past published scientific literature to corroborate the likely impact of such erosion and new tidal inlets on the lake ecosystem. Experts differed on their opinions on how the plankton, fish, seagrass and critically endangered Irrawaddy Dolphin would respond to the salinity changes in the lake aftermath of the cyclone. Some of the impacts of ‘Fani’ on the lake shoreline and ecosystem were imminent, such as the opening of tidal inlets and spot death of three Irrawaddy dolphins; whereas, long-term impacts such as changes in the biomass and composition of plankton communities, fish and bird population in the lake are primarily unknown and warrants further detailed investigation. Nevertheless, the study asserts that cyclone driven shoreline damage can impact lagoon ecosystem by bringing in a rapid change in the salinity field

Abstract: Rising sea levels are causing more frequent flooding events in coastal areas and generate many issues for coastal communities such as loss of property or damages to infrastructures. To address this issue, this paper reviews measures currently in place and identifies possible control measures that can be implemented to aid preservation of coastlines in the future. Breakwaters present a unique opportunity to proactively address the impact of coastal flooding. However, there is currently a lack of research into combined hard and soft engineering techniques. To address the global need for developing sustainable solutions, three specific breakwater configurations were designed and experimentally compared in the hydraulic laboratory at Coventry University to assess their performance in reducing overtopping and the impact of waves, quantifying the effectiveness of each. The investigation confirmed that stepped configurations work effectively in high amplitudes waves, especially with the presence of a slope angle to aid wave reflection. These results provide a very valuable preliminary investigation into novel sustainable solutions incorporating both artificial and natural based strategies that could be considered by local and national authorities for the planning of future mitigation strategies to defend coastal areas from flooding and erosion.

Abstract: Harnessing the advantages of geotextile sand containers (GSCs), numerous submerged breakwaters and shoreline protection structures have been constructed worldwide. But an emerged breakwater structure with geotextile armour units, capable of replacing the conventional structures, is rarely discussed. A 1:30 scaled physical experimentation is chosen as a preliminary investigation to test the feasibility of using GSCs as breakwater armour units. Structural design is evolved based on a comprehensive literature survey. The paper focuses on the stability parameters and damage characteristics of the proposed structure. Four different configurations are subjected to waves, confining to Mangaluru's wave parameters. Effect of armour unit size and sand fill ratio on the stability of the structure is analysed and it is concluded that changing sand fill ratio from 80% to 100% shot up the structural stability to a maximum of 14%. Increasing bag size also resulted in the increased stability up to 8%. Experiments revealed that the best performing configuration could withstand wave heights up to 2.7 m. Stability curves for all tested configurations are discussed and can serve as an effective guideline for designing GSC breakwaters.