Browsing by Author "Hettiarachchi, SSL"

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Application of management frameworks for coastal zone management
Hettiarachchi, SSL
Sri Lanka is an island state with a coastline of approximately 1600 km and a land area of around 64,000 sq. km. Coastal erosion has been identified as a major natural hazard faced by Sri Lanka for a very long time. Its impact has increased at alarming rates due to unplanned human intervention in the coastal zone and with more than half of the country's total population settled in coastal areas, the unplanned development of coastal infrastructure resulting from increased settlements has naturally led to accelerated degradation of the coastal environment. Although the coastal problems of Sri Lanka have been recognized from the turn of the century it is in the last two decades that growing attention has been focused on these problems because they have been seriously aggravated
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Application of mathamatical modelling in investigating coastal phenomena
(12/2/2011) Wijesekara, GN; Hettiarachchi, SSL; Samarawickrama, S
With the evolvement of Information Technology, the simulation of physical theories on real matter in order to envisage the behavior of man-made structures and its impact on earth resources have “spread its wings” from scaled models to highly sophisticated virtual reality computer models where all elements can be viewed in 2D/3D in graphic user interfaces. Particularly the study in Coastal wave mechanics and simulation of such uncertainty with man-made structures, have proven the value of technology and it has been much effective with cost and time. With the current research that had been carried so far, commercially used in-house wave models were studied and a whole new design and analysis of a computer simulated numerical model for Sediment Transport Modelling was carried out. Case study on Hambanthota describes the coastal processes that has been undertaken in order to investigate the wave climate, wave induced currents and sediment movement for the proposed fishery harbour at Hambathota in Sri Lanka. Various components of an available wave modelling suite (“Halcrow”) were applied to evaluate the nearshore wave climate for design purposes, for optimization of the harbour configuration, for examination of wave penetration and for the input to the beach evolution model. The wave modelling shows that there is no significance wave penetration for the proposed fishery harbour. In addition, Wave-induced current modelling and investigation of beach evolution of the existing bay has been undertaken. The proceedings of a final year project discussed on environmental impact on ecological and social environment with several proposed alternatives for a fishery harbour in Negombo Lagoon were considered for a case study using a commercial wave model to examine the significance impact of the wave climate for the nearshore region and structures proposed to be located in Negombo Bay. Several components of “Halcrow” wave model are used in order to validate the first alternative and modifications required are suggested herewith. Most important of all, a sophisticated numerical model is designed and analyzed with the use of paradigms of software engineering for the simulation of Alongshore Abstract Sediment Transport. Equations by Kamphuis (1992) based on empirical co-relations and dimensional analysis of properties have been used and followed through the whole design. Theories and equations integrated from research carried out by Dr. Saman Samarawickrama were used in deriving solutions for the numerical model of which the design is based on many GIS (Geographical Information System) functionalities.
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Assessment of vulnerability in relation to Tsunami risk assessment
Hettiarachchi, SSL
Planning post tsunami rehabilitation and conservation of the Sri Lankan coastline should ideally be undertaken within a multi hazard coastal risk assessment framework giving due consideration to all the coastal hazards. Even when risk assessments are undertaken only for the tsunami hazard it is important to conduct such studies on a platform which can accommodate other coastal hazards. For risk assessment against the tsunami hazard it is important to assess scientifically and establish the basis and criteria on which such an exercise is undertaken. Planning based on observations arising from a single extreme event without scientifically analyzing the true character of potential events, their impacts and future threats and risks should be avoided
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Coastal and environmental impacts arising from major coastal infrastructure development projects
Soysa, VAN; Samarawickrama, SP; Hettiarachchi, SSL
Sri Lanka being an island state, strategically located in the Indian Ocean, has a high potential for the developments of its economy in the coastal zone. During the reason past, there have been major development projects undertaken by the Government of Sri Lanka including the developments of ports, tourism industry and urban development. At the same time, it must be noted and recognised that the coastal zones are environmentally very sensitive and have to be conserved in order for well-being of unique coastal eco-system, This conflict between development and conservation has raised major issues among the environmental protectionist. Such groups have raised concerns of the impacts of development project on the coastal zone. Although many coastal region development projects have been undertaken, hardly any project has been monitored to study its impact on the environment. In this respect, planned monitoring of Colombo South Harbour (CSH) project, one of the largest engineering projects to be undertaken in Sri Lanka, provided an excellent opportunity to study the impacts arising from appreciable disturbances to the seabed and neighbouring regions. The analysis of this monitoring, which is the major part of this research study identifies the extent of impact arising from mega coastal projects. Both CSH and associated Loading Out Point (LOP) at Wadduwa have therefore been considered, In addition, it focused on the Kirinda Fishery Harbour project, which failed in the first instances as well as after rehabilitation. The impact on vessels manoeuvring during extreme hazardous condition was investigated via the case study of Shimoda port Japan, undertaken by the researcher during a training programme at Port and Airport Research Institute, Japan. From this research study, it is concluded that no significant coastal environment impacts are raised due to CSH project as far as sea water quality, air quality and suspended particles levels are concerned. However, threshold values for noise levels were frequently exceeded at quarry site. Further, LOP at Wadduwa indicated severe erosion at northern sections, and significant accumulation at southern sections. Observed data and calculations revealed that with the beach nourishment, for duration of a month, still amount of over 900 m3 of volume for a stretch of 50 m along the coastline, eroded around 0+150 N to 0+500 N and the value decreases to 250 m3 around 0+750 N to 0+900 N. From the results of numerical simulations for drifting bodies at Shimoda port, specific locations were identified as the safest and most suitable locations to be developed for berth and moor purposes at Shimoda port minimizing the intensity and probability of collision hazard. It is expected that detailed research studies will high-light the extent of impacts on the coastal zone of large civil engineering projects which interact with coastal water. Such interaction includes dredging, reclamation, construction of major coastal works, and its impact on livelihood of the coastal community during and after construction. In the absence of detailed monitoring during and after construction, one would only speculate the long term impacts without cross comparison with prevalent condition away from projects.
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Damage mechanism of Hikkaduwa due to December 2004 Indian Ocean tsunami
(2007) Welhena, T; Samarawickrama, SP; Hettiarachchi, SSL
More than two thirds of the Sri Lankan coastline got affected from the December 2004 Indian Ocean Tsunami. Field surveys conducted clearly indicate that some of the cities in the western coast of Sri Lanka in the shadow of the incident tsunami experienced significantly high damage similar to that of the eastern coast which was directly facing the incident tsunami. Destruction caused by the tsunami in the western coast was patchy and the cities like Galle and Hikkaduwa could be identified as the worst affected. In the case of Galle, the Bay and Headland combination would have increased the height and speed of the Tsunami wave and the damages accordingly. Even without such prominent coastal features Hikkaduwa experienced a similar scale of damages. This led to the investigations in identifying the damage mechanisms of Hikkaduwa where inundation and wave heights were as much as 5-10 times of the surrounding areas of the south west coast. Such complex mechanism of damages can be interpreted via results of Numerical Modeling and analysis of the existing coastal features in Hikkaduwa.
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Development of an analytical model to studywave motion to through porough porous vertical to coastalstructures
Samarasekara, MMPD; Hettiarachchi, SSL
This study is concerned with the development of an analytical model to predict wave reflection and transmission characteristics of porous, vertical coastal structures. Because of the complexity of the problem the study was limited to non-breaking, small amplitude, long waves normally incident to the structure. The input data for the model are the incident wave characteristics and the properties of the porous media. The wave climate is identified by the wave height, the wave period and still water depth. The porous structure is characterised by its length, overall porosity and the laminar and turbulent flow coefficients (determined under steady flow conditions). The Forchheimer equation was used for the hydraulic gradient-velocity relationship. Continuity and momentum equations are linearised for the inclusion in the model. The model was verified with results obtained from hydraulic model investigations carried out at Imperial college, London and Lanka hydraulics institute, Sri Lanka. Satisfactory agreement was obtained between experimental and predicted values. 11
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Disaster management frameworks in Sri Lanka and compliance with global standards
Jayasiri, GP; Hettiarachchi, SSL; Siriwardana, CSA
In the recent past Sri Lanka has experienced several significant natural disasters. At present, the DMC and all the line agencies focus on disaster management functions under the ministry of disaster management. The comprehensive disaster management program was prepared in 2014 and it is to be used up until 2018. Furthermore, it was proposed to identify mechanisms to integrate the Sendai Framework into the Sri Lankan national disaster management framework. However, during recent disasters, the DMC and the disaster management framework was under severe criticism from the public as well as the technical community. Therefore, the aim of this study is to investigate disaster management framework in Sri Lanka and its compliance with global standards. Initially an in-depth literature review was carried out to identify the terminology and existing local and international frameworks related to Disaster Management. Then the local frameworks were evaluated against seven criteria, which were identified after carefully analysing the requirements of the Sendai Framework. During this investigations several recent disaster incidents were referred as well. In addition, a case study was carried out to identify the status of some of the key components of coastal community resilience. Interviewing key professionals in the field of Disaster Risk Reduction in Sri Lanka and the focused group and panel discussions provided sufficient data for the analysis. Sri Lanka is in the process of aligning themselves with the Sendai Framework and Even though country lacks proper and efficient resilience mechanisms focused on the coastal communities, national efforts are underway to build up the coastal resilience. Training and public awareness campaigns, efficient funds, properly maintained hierarchy and concern to the coastal ecosystems are some of the enablers associated in building coastal resilience. Developing a multi-hazard map, improving the interagency cooperation, Use of social media to disseminate Early Warnings and focusing more on the development of a people-centered Multi-Hazard Early Warning Systems (MHEWS) are some of the recommendations given.
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Drainage and exclusion of salt-water in low-lying coastal areas — a case study from the Southern Province of Sri Lanka
(Elsevier, 1997) Hettiarachchi, SSL
Storm-water drainage and salt-water exchange are two important phenomena which should be incorporated in an environmental management programme of an estuarine ecosystem. This paper presents the results of an investigation to study, within an integrated management framework, the problems associated with salt-water exclusion and drainage in the Southern Province of Sri Lanka. This paper recognizes the relevance of identifying the relationship between the impact of development activities and other parameters which influence salt-water intrusion. The need to adopt coastal engineering techniques to keep the outfalls open free from sand bar formation while maintaining a stable coastline on either side is discussed. This paper identifies the importance of adopting well-formulated estuarine management strategies, which give priority to the continual existence of the natural estuarine environment and consider both the resources of the ecosystem as well as the demand for its exploitation.
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Drainage and exclusion of salt‐water in low‐lying coastal areas: A case study from the Southern Province of Sri Lanka
Hettiarachchi, SSL
Storm‐water drainage and salt‐water exchange are two important phenomena which should be incorporated in an environmental management programme of an estuarine ecosystem. This paper presents the results of an investigation to study, within an integrated management framework, the problems associated with salt‐water exclusion and drainage in the Southern Province of Sri Lanka. This paper recognizes the elevance of identifying the relationship between the impact of development activities and other parameters which influence salt‐water intrusion. The need to adopt coastal engineering techniques to keep the outfalls opens free from sand bar formation while maintaining a stable coastline on either side is discussed. This paper identifies the importance of adopting wellformulated estuarine management strategies, which give priority to the continual existence of the natural estuarine environment and consider both the resources of the ecosystem as well as the demand for its exploitation.
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EMERGING COMPETENCIES WITHIN NATIONAL AND LOCAL GOVERNMENT FOR SOCIETAL RESILIENCE TO DISASTERS IN SRI LANKA
(2016-08-29) Hettiarachchi, SSL; Goonasekera, H; Gunatilake, S; Weeresinghe, S
Emerging competencies for societal resilience to disaster within the built environment domain of Sri Lanka were analysed in the aim of developing a professional doctoral (DProf) course through the CADRE (EU-FP7) project. Competencies were compiled following the amalgamation of both emerging market needs and skills within the built environment domain of Sri Lanka. In its investigation, qualitative and quantitative data collection was facilitated through a literature review. Data collection was conducted in respective to all stages of the construction cycle (i.e. Preparation, Design, Pre-construction, Construction, Use). The analysis was conducted using resilience themes for five thematic areas (i.e. social, technological, environmental, economic and institutional) in relation to each stage of the construction cycle. Despite local and national government bodies affecting a central role in policy, planning and implementation of land use changes and construction, built environment professionals with specialised expertise was minimal. Parallels were drawn regarding the gaps within the private sector and local and national government, such as a critical need for skills development programmes to ensure a viable skilled labour force and job security. Finally, it is critical for national and local government to enforce existing certification systems and standards for skilled workers to ensure a safe, viable and competitive construction industry.
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Emerging competencies within national and local government for societal resilience to disasters in Sri Lanka
(Ceylon Institute of Builders, 2016-07) Hettiarachchi, SSL; Goonasekera, H; Gunatilake, S; Weeresinghe, S; Sandanayake, YG; Karunasena, GI; Ramachandra, T
Emerging competencies for societal resilience to disaster within the built environment domain of Sri Lanka were analysed in the aim of developing a professional doctoral (DProf) course through the CADRE (EU-FP7) project. Competencies were compiled following the amalgamation of both emerging market needs and skills within the built environment domain of Sri Lanka. In its investigation, qualitative and quantitative data collection was facilitated through a literature review. Data collection was conducted in respective to all stages of the construction cycle (i.e. Preparation, Design, Pre-construction, Construction, Use). The analysis was conducted using resilience themes for five thematic areas (i.e. social, technological, environmental, economic and institutional) in relation to each stage of the construction cycle. Despite local and national government bodies affecting a central role in policy, planning and implementation of land use changes and construction, built environment professionals with specialised expertise was minimal. Parallels were drawn regarding the gaps within the private sector and local and national government, such as a critical need for skills development programmes to ensure a viable skilled labour force and job security. Finally, it is critical for national and local government to enforce existing certification systems and standards for skilled workers to ensure a safe, viable and competitive construction industry.
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Energy dissipation characteristics of rock armoured rubble mound breakwaters
(1999) Hettiarachchi, SSL; Mirihagalla, PD
The paper presents the results of large scale physical model investigations on the hydraulic performance of rock armoured rubble mound breakwaters. The energy dissipation characteristics of conventional trapezoidal layered breakwaters and berm breakwaters, both statically and dynamically stable are presented. The hydraulic performance of the structures are evaluated as a function of the incident wave parameters.
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Experience of the Indian Ocean tsunami on the Sri Lankan coast
(2005) Hettiarachchi, SSL; Samarawickrama, SP
The Indian Ocean Tsunami de 'r-stated the- coastline of Sri Lanka. This paper sumrnarises the initial efforts in understanding the tsunami wave and its hydraulic impact on the Sri Lankan coastline. It focuses attention on the hydraulic processes which led to large scale inundation, analysis of wave- current measurements recorded offshore of Colombo Harbour and describes post tsunami field investigations to assess the overall impact on the coastline. The paper identifies the need for modeling of potential tsunamis and discusses briefly issues relating to the planning of countermeasures.
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Hydraulic Performance of ‘HOBO’ units
(2015-08-03) Odara, MGN; Hettiarachchi, SSL; Mirihagalla, PD
The paper presents the results of a detailed two dimensional model investigation of a rubble mound breakwater armoured with Hollow Block (HOBO) concrete armour units, with respect to the hydraulic performance. The results of the model investigations are analysed to obtain graphical and numerical relationships between the energy dissipation, wave reflection, energy transmission, wave steepness, wave period, Iribarren number and the section properties of the breakwater.
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Hydraulic performance of ‘HOBO’ units
Odara, MGN; Hettiarachchi, SSL; Mirihagalla, PD
The paper presents the results of a detailed two dimensional model investigation of a rubble mound breakwater armoured with Hollow Block (HOBO) concrete armour units, with respect to the hydraulic performance. The results of the model investigations are analysed to obtain graphical and numerical relationships between the energy dissipation, wave reflection, energy transmission, wave steepness, wave period, Iribarren number and the section properties of the breakwater.
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Hydraulic performance of coastal and harbour structures
(2014-07-07) Thilakarathne, UGT; Hettiarachchi, SSL
The main focus of the research study is the development of an analytical model for the prediction of reflection and transmission coefficients of porous vertical structures of both the open and close (absorber) types. Having developed governing equations for the. different flow regions, appropriate boundary conditions and other justified simplifications have to be adopted in order to develop a solution. The input data for the model are the incident wave characteristics and the properties of the porous media. The wave climate is identified by its height, the wave period and still water depth. The porous structure it self is characterized by its length, overall porosity and the flow coefficients in the Forchcheimer equation ( I = au + b u 2 ) . The model was verified with results obtained from hydraulic model investigations conducted previously. This study incorporates a literature review and presents the results of hydraulic performances especially on wave reflection and transmission characteristics of a wide range of structures varying from vertical, homogeneous sloping, multi layered sloping and berm configurations. Hydraulic model test can provide reliable method to quantify many of the wave structure response functions for sea walls and breakwaters. But fewer experiments have been carried out of these structures in Sri Lanka especially on berm structures. Therefore a detailed hydraulic model investigation (1:20) relating to the hydraulic performances of berm breakwater with berm width of 6m was done as a part of this study. It was tested in Lanka Hydraulic Institute (LHI), Katubedda, Moratuwa. The results are compared with a model investigation done on a berm structure with the berm width of 12m at a scale of 1:20 (also tested in Lanka Hydraulic Institute in 1999).
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Hydraulic performance of porous vertical coastal Structures
(Engineering Research Unit, Faculty of Engiennring, University of Moratuwa, 1997-11) Hettiarachchi, SSL; Hettiarachchci, P
Porous vertical structures have been used for coast protection and for harbour structures. In the case of harbours these structures have been used as the principal breakwaters and as internal structures. The ability to predict the level of reflection and transmission plays an important role in the assessment of their hydraulic performance. This paper identifies the relative advantages of using porous vertical structures in practice and focuses attention on the hydraulic performance of a range of such structures with specific reference to energy dissipation characteristics in relation to their hydraulic design.
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Hydraulic Performance Of Rubble Mound Breakwaters
(2014-06-10) Hettiarachchi, SSL; Odara, MGN; Godagedara, TH; Herath, HHHB
Breakwaters are widely used to mitigate the adverse impacts of ocean wave action. Breakwater failures that occurred during late seventies and early eighties, have highlighted the need for further investigations on breakwaters in terms of their hydraulic performance. This paper presents the hydraulic performance of conventional rubble mound rock armoured breakwaters and concrete armoured rubble mound breakwaters, statically stable berm breakwaters and reshaping berm breakwaters based on the re-analysis of large scale model tests.
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Hydraulic performance of rubble mound breakwaters
(Department of Civil Engineering, University of Moratuwa, 2014-03) Hettiarachchi, SSL; Odara, MGN; Godagedara, TH; Herath, HHHB; Hettiarachchi, MTP
Breakwaters are widely used to mitigate the adverse impacts of ocean wave action. Breakwater failures that occurred during late seventies and early eighties, have highlighted the need for further investigations on breakwaters in terms of their hydraulic performance. This paper presents the hydraulic performance of conventional rubble mound rock armoured breakwaters and concrete armoured rubble mound breakwaters, statically stable berm breakwaters and reshaping berm breakwaters based on the re-analysis of large scale model tests.
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Hydraulic performance of statically stable berm breakwaters & gabion structures
Fernando, KPM; Hettiarachchi, SSL
The ability to predict the level of reflection, transmission and dissipation for various types of coastal structures plays an important role in the assessment of their hydraulic performance. These parameters together with the hydraulic, geotechnical and structural stability of the individual components and of the structure as a whole determine the overall performance of the structure. This study has done a literature review and presents the results from a study of the hydraulic performances especially on wave reflection and transmission characteristics of a wide range of structures (vertical, sloping and berm) used in harbour and coastal engineering. Hydraulic model test can provide reliable method to quantify many of the wave structure response functions for breakwaters. A detailed hydraulic model investigation (1:20) relating to the hydraulic performances of berm breakwater with berm width of 6m was done as a part of this study. It was tested in Lanka Hydraulic Institute (LHI), Katubedda, Moratuwa. The results are compared with a model investigation done on a berm structure with the berm width of 12m at a scale of 1:20 (also tested in Lanka Hydraulic Institute in 1999) and Allsop and Channel (berm widths of 4m, 8m and 16m) test sections. The investigations were designed to obtain a full profile of the energy dissipation characteristics of the structures tested, including the damping of waves as they propagate through the structure.