Browsing by Author "Ratnasooriya, AHR"

Now showing 1 - 20 of 21

item: Article-Abstract
Ageing of pipes and sustainability of water supply
Ratnasooriya, AHR; Wijesekera, NTS
With ageing, the sustainability of the level of service of water supply in a pipe network may be adversely affected due to the reduction of flow rates caused by corrosion or scale deposition in pipes. In this study, attention is focussed on the effect of scaling on frictional losses in pipes and increased roughness values for pipes, based on experimental investigations, are presented. The influence of scaling on the performance of a small pipe network is analysed and relevant design issues are discussed.
item: Conference-Abstract
Assessment of tsunami hazards and exposure of sri lanka: case study in south-western coast
(Department of Civil Engineering, 2023-09-27) Kanishka, UAM; Ratnasooriya, AHR; Mallikarachchi, C; Hettiarachchi, P; Herath, S; Fernando, L
This research focuses on assessing the exposure of Sri Lanka's southwestern coast to tsunami hazards. Tsunamis are a series of ocean waves triggered by impulsive disturbances, such as undersea earthquakes, volcanic eruptions, landslides, and cosmic explosions. The catastrophic impact of tsunamis, as demonstrated by the devastating Indian Ocean tsunami (IOT) event in December 2004, underscores the urgent need for an effective early warning system to mitigate the loss of life and property in coastal regions. The study specifically examines the vulnerability and exposure of the southern coastline ranging from Rathgama to Dadalla. The Community Model Interface for Tsunami (ComMIT) is used in the research's numerical simulation. Access to a precomputed tsunami scenario database and the MOST (Method of Splitting Tsunami) model created by the NCTR (National Center for Tsunami Research) is made possible through ComMIT, a user-friendly graphical interface. The model simulates tsunami waves with magnitudes ranging from 7.6 to 9.2 Mw, originating from selected unit sources along the Sunda trench in Indonesia and the Makran fault in Pakistan. The Sunda Arc is a volcanic arc that formed the islands of Java and Sumatra. Makran fault is located to the northwest off the coast of Pakistan. Makran trench is less affected relative to Sunda arc. For this research study five zones in Sunda trench and one zone in Makran fault are taken for segmentation of unit sources. By combining the model's output with Green's law, the research calculates the maximum wave heights at a depth of 1 m. This data is crucial in identifying the levels of tsunami exposure along the coastal stretch. Furthermore, it enables the accurate projection of the exposure, facilitating the incorporation of lag-time effectively into early warning systems. The findings of this study will contribute to enhancing the understanding of tsunami hazards in Sri Lanka and specifically the southwestern coastal region. Exposure assessment will aid in issuing timely and accurate warnings, minimising the potential for fatalities and injuries in future tsunami events. Ultimately, the research aims to improve disaster preparedness and enhance the resilience of coastal communities in Sri Lanka to mitigate the impacts of tsunamis.
item: Conference-Full-text
Coastal erosion: investigations in the southwest coast of Sri Lanka
(2013-11-19) Wijayawardane, ISK; Ansaf, KMM; Ratnasooriya, AHR; Samarawickrama, SP
Sri Lanka is an island with a coastline of length approximately 1600 km. Coastal erosion has been identified as a major hazard in many coastal areas, particularly along the densely populated southwest coastline of the country. Numerical studies were conducted to assess the sediment transport rates in selected areas along the southwest coast. Field investigations were carried out at several locations to assess the behaviour of the coastline. In this on-going study, seasonal trends of sediment transport rates are to be assessed and compared with measured shoreline behaviour.
item: Conference-Extended-Abstract
The effect of scaling on frictional losses in pipes
(2007) Wijesekera, NTS; Ratnasooriya, AHR
The ability to predict the hydraulic performance of a pipe network during its working life plays an important role in the planning and design of water supply schemes. The nominal diameter and the friction factor of pipes are two essential parameters in the analysis of pipe networks. The values of these parameters are usually known for commercially used new pipes. With aging, corrosion and scaling in pipes may cause a reduction of diameter and an increase in surface roughness, leading to a reduction of carrying capacity. In this experimental study, attention is focused on the effect of scaling on frictional losses of commercially used pve pipes.
item: SRC-Report
Frictional resistance in fluid flow
(2016-08-22) Ratnasooriya, AHR
Title of the Publication "Mitigation of Tsunami inundation by costal vegetation"
item: Thesis-Abstract
Global climate change : impact on the coastal zone of Sri Lanka
Wijayawardane, ISK; Ratnasooriya, AHR; Samarawickrama, SP
It is unequivocal that sea level is rising and it will further exacerbate the already existing problems in the coastal regions. With the increase of greenhouse gases, the global warming which is the main factor affecting the sea level rise has accelerated. Rise in sea level can cause many problems in the socio-economic activities and coastal eco systems due to coastal erosion, inundation, salt water intrusion, etc. Therefore countries having low lying coastal areas need to pay attention on this before the problems become worst. This study was conducted in order to assess the shoreline variation due to SLR in southwest coast of Sri Lanka. Four coastal locations (Ambalangoda, Bentota, Kalutara and Lunawa) were selected which have different morphological features. Nearshore wave climates at those locations were established considering SLR scenarios established by IPCC (Intergovernmental Panel on Climate Change) in 2007. Offshore wave measurements were used for the analysis. In establishing nearshore wave climate MIKE21 Nearshore Spectral Wave Model was used and the shoreline recession was estimated for different scenarios by Bruun Rule. In addition change in wind direction and speed considered only at Lunawa. The established nearshore wave climate shows a clear increase in significant wave height in both sea and swell waves at all the locations with the increase of sea level. However the changes in mean wave period and in mean wave direction at nearshore are not significant. Shoreline recession caused by sea level rise varies from place to place depending on the wave climate and the morphological features of the area. Generally shoreline recession is 50 to 120 times the sea level rise.
item: Conference-Full-text
Global climate change impacts on wave energy potential along the south coast of Sri Lanka
(IEEE, 2020-07) Maduwantha, MGP; Karunarathna, HU; ukKamranzad, B; Ratnasooriya, AHR; De Silva, PKC; Weeraddana, C; Edussooriya, CUS; Abeysooriya, RP
The direct south-west swell wave approach and relatively narrow continental shelf create more favorable conditions for wave energy harvesting in Sri Lankan coastal region. South coast of Sri Lanka has the most energetic ocean waves which are highly modulated by the south-west monsoon winds. In this study, numerically projected ocean waves simulated using Simulating Waves Nearshore (SWAN) model for two time slices which represent the 'present' and 'future' (end-of-century) are used to evaluate the impact of global climate change on wave energy resource in the south coast of Sri Lanka. The results reveal that there will be a slight reduction of average available wave power in the west, south and east coasts of Sri Lanka in the future. Changes of wave heights during the south-west monsoon season can be identified as the reason for this reduction of wave power.
item: Thesis-Abstract
Hydro-geotechnical behaviour of porous coastal structures
Ratnasooriya, AHR; Hettiarachchi, SSL
Theoretical modeling of the flow field in the vicinity of a porous coastal structure was carried out to investigate the hydro-geotechnical behaviour of such a structure. The area of interest consists of the regions in front of and within the structure and in the sub soil below the sea bed, resulting in three inter-related flow models, External Flow, Internal Flow and the Pore Pressure Response Models. In the External Flow Model, the governmg equations are based on the principles of conservation of mass and momentum and were solved numerically by an explicit finite difference method. The model was shown to yield the flow characteristics and the computed wave run-up, run-down and reflection coefficient were shown to be in qualitative agreement with the available empirical formulae. The governing equations in the Internal Flow Model are also based on the principles of conservation of mass and momentum and were solved by a mixed numerical technique involving a combined finite difference-method of characteristic scheme and a finite element method. The model was shown to represent the two dimensional nature of flow and yield satisfactory agreement with the experimental data for the position of the phreatic surface. In the Pore Pressure Response Model, the governing equation for the flow in the soil is based on the principle of conservation of mass with the generation of pore pressure represented by an empirical expression. An explicit finite difference method was used to solve it and the solution provides the complete time history of pore water pressure response due to cyclic wave loading. With the flow models shown to be capable of simulating the flow field in the vicinity of a porous coastal structure, this study forms a basis for further studies aiming at supplementing the design practices of such structures presently based on physical modeling and empirical formulations.
item: SRC-Report
Improved tusnami wave height forecasting – an integrated approach for the analysis of results from early warning systems and inundation modelling for risk assessment
Hettiarachchi, SSL; Ratnasooriya, AHR; Samarasekera, RSM
A Tsunami Warning System must alert all persons on every vulnerable coast of imminent danger, covered by the system. The response of such a system must be rapid (as soon as possible), accurate (minimize false warning), reliable (continuous operation), effective (to save lives). UN-ISDR Framework for effective Early Warning Systems encompass four critical linked elements (Figure 1), • Detection, Monitoring and Warning Service (Technical Monitoring and Warning Service) • Risk Knowledge (Awareness of the Risk) • Dissemination and Communication (Dissemination of meaningful warnings to Persons and Communities at Risk) • Response Capability (Public Awareness and Preparedness to Respond)
item: Thesis-Abstract
Investigations on coastal sediment transport and shoreline behaviour
Ansaf, KMM; Ratnasooriya, AHR; Samarawickrama, SP
The ever-increasing economical and environmental considerations of coastal areas have provoked further studies of the variety of processes taking place in the coastal zone. This thesis elaborates a study conducted to quantify the coastal sediment transport rates along the Southwest coast of Sri Lanka. Representative near-shore wave climates have been established for the individual coastal cells along the considered coastline from Galle to Colombo. Available Galle offshore data measured at 70 m depth was used for the stated purpose with the help of MIKE 21 NSW numerical modelling tool. A statistical analysis was performed with the offshore wave records to identify the wave occurrence probability, and clear variations between the seasons were observed. The model has been validated with observed wave data in Hikkaduwa at 15 m depth near-shore and found that the model is accurately applicable for the Southwest coast. Near-shore wave climates were prepared separately for swell and sea conditions versus their occurrence probability. Kamphuis (2002) model is found to be simple and reliable for the sediment transport computation of the Sri Lankan coast. This computation has revealed that the highest sediment transportation takes place during the Southwest monsoon period. Sediment transportation induced by the swell wave conditions dominates over the sea waves. An annual net sediment transport rate of 105 m3 was obtained across all the cells along the Southwest coast. The direction of movement is towards north in almost all the cells. These transport rates could be termed as long-term and one dimensional morphology model was used to find possible monthly shoreline movement in various seasons. A series of field measurements carried out, have helped in understanding and determining seasonal changes of shoreline, local erosion/accretion behaviour, and representative median sediment size for the individual cells. The study can be considered as a new approach to quantify coastal sediment transport rates and to understand shoreline behaviour in Southwest coast of Sri Lanka.
item: Article-Full-text
Mitigation of Tsunami inundation by coastal vegetation
(The Institution of Engineers, 2008) Ratnasooriya, AHR; Samarawickrama, SP; Hettiarachchi, SSL; Bandara, RPSS; Tanaka, N
In the aftermath of the Indian Ocean Tsunami disaster in 2004, the protection offered by coastal vegetation has become evident in many countries affected and the role of vegetation as a possible tsunami impact mitigation measure has been identified. A study was conducted to assess the effectiveness of vegetation in mitigating tsunami inundation in which small scale physical model tests were carried out to investigate the influence of various characteristics of the vegetation in reducing the extent of inundation. Significant reduction levels of inundation were observed in the testing program and the relative influences of the location, density, extent and pattern of vegetation were identified.
item: Conference-Full-text
Non-revenue water reduction strategies for an urban water supply scheme: a case study for Gampaha water supply scheme
(IEEE, 2023-12-09) De Silva, WSD; Ratnasooriya, AHR; Abeykoon, H; Abeysooriya, R; Adikariwattage, V; Hemachandra, K
Many urban water supply schemes face numerous challenges, including inadequate water supply relative to public demand, outdated infrastructure causing water losses, leading to substandard services throughout the distribution process. The presence of high levels of Non-Revenue Water (NRW) further exacerbates these challenges, coupled with limited availability of funds. NRW poses a barrier to sustainability due to energy and water losses. Therefore, this research aims to focus specifically on addressing the issue of NRW to contribute to sustainable water management. The research objectives include exploring water losses in the transmission and distribution systems, primarily attributable to leakages, and evaluating the performance of individual water pipes. To accomplish the objectives, the study employs the Analytic Hierarchy Process (AHP) to assess various factors contributing to pipe leakages. The AHP methodology enables the identification and prioritization of key factors influencing pipe leakages, providing valuable insights for enhancing the performance and maintenance of water distribution systems. By identifying the factors contributing to pipeline leakage, proactive measures can be implemented to prevent and control leaks at an early stage, thereby shifting from a reactive to a proactive approach in water management. This transition will enable the industry to detect and address leakage issues more effectively, leading to improved overall water management and a reduction in NRW. The research focuses on the Gampaha Water Supply Scheme as a case study, aiming to develop effective strategies for reducing NRW. The findings of this research will provide practical recommendations for policymakers and water management authorities to optimize water supply systems, minimize losses, and enhance sustainability in urban water supply schemes.
item: Conference-Abstract
Non-revenue water reduction strategies for an urban water supply scheme:a case study for gampaha water supply scheme
(Department of Civil Engineering, 2023-09-27) De Silva, WSD; Ratnasooriya, AHR; Mallikarachchi, C; Hettiarachchi, P; Herath, S; Fernando, L
The urban water supply industry faces numerous challenges, including inadequate water supply relative to public demand, outdated infrastructure causing water loss, substandard services throughout the distribution process, and management and staff mindset towards service provision. Rapid urbanisation and population growth have further strained water resources and infrastructure, exacerbating these challenges. The presence of high levels of Non-Revenue Water (NRW), which encompasses both physical losses (leakages) and commercial losses (unauthorised consumption and inaccurate metering), further exacerbates these challenges, coupled with limited availability of funds for infrastructure improvement and maintenance. NRW poses a barrier to sustainability not only due to energy and water loss but also due to revenue loss for water utilities, impacting their financial viability. Therefore, this research aims to focus specifically on the issue of NRW to contribute to sustainable water management, addressing both environmental and economic concerns. The research objectives include not only exploring and discussing water losses in the transmission and distribution system but also analysing the socio-economic factors that contribute to NRW. By delving into the socioeconomic aspects, the study aims to provide a holistic understanding of the issue, considering factors such as affordability, consumer behavior, and illegal water tapping. To accomplish these objectives, the study employs the Analytic Hierarchy Process (AHP), a widely recognised decision-making tool that allows for a structured evaluation of complex multi-criteria problems. By utilising AHP, the research assesses various factors contributing to pipe leakages and NRW. The AHP methodology enables the identification and prioritisation of key factors influencing pipe leakages, providing valuable insights for enhancing the performance and maintenance of water distribution systems. By identifying the factors contributing to pipeline leakage and NRW, proactive measures can be implemented to prevent and control leaks at an early stage, thereby shifting from a reactive to a proactive approach in water management. This transition will enable the industry to detect and address leakage issues more effectively, leading to improved overall water management and a reduction in NRW. The research also acknowledges the importance of public awareness campaigns and community engagement in reducing NRW, as informed consumers can play a crucial role in leak detection and reporting. The research focuses on the Gampaha Water Supply Scheme as a case study due to its relevance to the challenges faced by urban water supply systems in many developing countries. The findings of this research will provide practical recommendations for policymakers and water management authorities to optimise water supply systems, minimise losses, and enhance sustainability in urban water supply schemes. This research contributes to the ongoing discourse on sustainable urban water management by addressing the critical issue of NRW. Through these efforts, the research aims to pave the way for more resilient and efficient water supply systems that can cater to the needs of growing urban populations while minimising resource wastage and financial losses.
item: Conference-Extended-Abstract
Numerical modelling of tsunamis - case study from Galle
(2007) Samarawickrama, SP; Hettiarachchi, SSL; Ratnasooriya, AHR
In the context of Tsunamis the location of Galle is extremely vulnerable. It lies besides a wide bay and a natural headland on which is located the historic Galle Fort with very reflective vertical non-porous walls on all sides. In the vicinity of the headland on which the Galle Fort is located, the wave energy concentrates due to refraction. These waves then reflected from the vertical solid walls of the Fort and moved around the headland. Such walls reflect almost all the incident wave energy with very high wave heights at the wall itself. There is hardly any dissipation.
item: SRC-Report
Public awareness of Tsunami hazards in Sri Lanka
Samarawickrama, SP; Ratnasooriya, AHR; Hettiarachchi, SSL
The objective of this research study was to assess the degree of public awareness on tsunamis. The results of the study are useful in planning awareness programs, the preparation of the Hazard Maps and in the implementation of research findings of the other components of the overall research project. A questionnaire survey was carried out covering a sample of more than 1200 people. The survey covered around 600 members of the general public and 600 school children
item: Conference-Extended-Abstract
Resistance to tsunami inundation vegetation: an experimental study by coastal
(2007) Ratnasooriya, AHR; Samarawickrama, SP; Hettiarachchi, SSSL; Bandara, RPSS
More than two thirds of the coastline of Sri Lanka was subjected to inundation by the Indian ocean tsunami on 26 December 2004. The inundation distance and the associated damage caused by the tsunami varied widely with the local near shore wave height, topography and the hydraulic resistance offered to the overland flow. In addition to the ground surface resistance, the resistance offered by vegetation and man made features in the coastal zone are among the contributory factors to the hydraulic resistance. It is important to asses the resistance offered by coastal vegetation to the overland flow in order to identify its effectiveness as a tsunami impact mitigation measure. Such a measure would also have the duel advantages of being environmentally friendly and cost effective.
item: Thesis-Abstract
Tsunami hazards : impact mitigation by bio-shields
(2014-08-06) Hemanthi, TDHM; Hettiarachchi, SSL; Ratnasooriya, AHR
In the consequences of the Indian Ocean tsunami in 2004 and subsequent alerts in 2005 and 2007, the protection offered by bio shields such as sand dunes, coral reefs and coastal vegetation became evident in many countries affected and the role of coastal green belts in mitigating tsunami impacts has now been clearly recognized. In this research, exploring the effectiveness of bio shields as an environmental friendly and cost effective measure of tsunami impact mitigation was mainly concerned. The preliminary experimental and numerical model studies in investigating of resistance offered by coastal vegetation to tsunami overland flow were expanded to determine the energy dissipation characteristics and reduction in inundation extent in detail, in order to assess the effectiveness of coastal green belts in tsunami impact mitigation. The resistive forces offered towards the flow which depend on the characteristics of an individual plant and characteristics of the vegetation as a whole, have been assessed. For an individual plant, the inundation of the stem of plants without the aerial root system, and branch structure perhaps representing the most common type of coastal vegetation, was considered in the tests as well as the vegetation as a whole can be characterized by its location from the shoreline, extent of spread, density or spacing between plants, distribution pattern and the size of plants. Detailed experimental studies were conducted to assess energy dissipation characteristics in which the vegetation was represented by geometrically similar small scale models (approximately 1:100). Similar to preliminary studies, this study was also conducted in a hydraulic flume. The energy dissipation of flow through vegetation was determined under steady flow conditions and reduction in inundation extent was assessed under unsteady flow conditions where mass of water was released over a sloping surface. Reduction levels in energy dissipation were obtained in the range up to 48 % and the levels of reduction in inundation extent were obtained nearly up to 35 % in the experiments, which indicates the possibility of achieving significant levels of energy reduction of tsunami inundation by coastal green belts. The dependence of the level of inundation reduction on the level of energy dissipation was also investigated.
item: Conference-Full-text
Tsunami Hazards: Energy Dissipation And Impact Mitigation Using Bio Shields
(2014-06-10) Jayawardena, DMSS; Hewageegana, VH; Ratnasooriya, AHR
Tsunamis can cause severe destruction in coastal areas. Though the tsunami hazard itself cannot be mitigated nor eliminated, the vulnerable element can be protected by a variety of mitigation measures. Bio shields, including coral reefs, coastal sand dunes and vegetation have been known to provide protection against tsunami inundation. The protection provided by bio shields was evident after the Indian Ocean Tsunami in 2004 in many of the countries affected. In view of these circumstances, attention was focused in this study to identify the capacity of protection provided by bio shields. Small scale physical model tests have been carried out to identify the mitigation characteristics of bio shields in the form of coastal vegetation. This study focused on detailed analysis of the results obtained by model tests. The protection capacity offered by the vegetation was assessed by considering two aspects, namely energy dissipation and reduction in the extent of inundation
item: Conference-Full-text
Tsunami hazards: energy dissipation and impact mitigation using bio shields
(Department of Civil Engineering, University of Moratuwa, 2014-03) Jayawardena, DMSS; Hewageegana, VH; Ratnasooriya, AHR; Hettiarachchi, MTP
Tsunamis can cause severe destruction in coastal areas. Though the tsunami hazard itself cannot be mitigated nor eliminated, the vulnerable element can be protected by a variety of mitigation measures. Bio shields, including coral reefs, coastal sand dunes and vegetation have been known to provide protection against tsunami inundation. The protection provided by bio shields was evident after the Indian Ocean Tsunami in 2004 in many of the countries affected.*In view of these circumstances, attention was focused in this study to identify the capacity of protection provided by bio shields. Small scale physical model tests have been carried out to identify the mitigation characteristics of bio shields in the form of coastal vegetation. This study focused on detailed analysis of the results obtained by model tests. The protection capacity offered by the vegetation was assessed by considering two aspects, namely energy dissipation and reduction in the extent of inundation.
item: Conference-Extended-Abstract
Tsunami hazards: public awareness and response
(2007) Samarawickrama, SP; Ratnasooriya, AHR; Hettiarachchi, SSL; Lawrance, MKD; Kumara, GGA
The objective of this research study was to assess the degree of public awareness on tsunamis. The results of the study are useful in planning awareness programs, the preparation of the Hazard Maps and in the implementation of research findings of the other components of the overall research project. A questionnaire survey was carried out covering a sample of more than 1200 people. The survey covered around 600 members of the general public and 600 school children.