Browsing by Author "De Silva, PKC"

Now showing 1 - 6 of 6

item: Conference-Abstract
Analysis of multi-day extreme rainfall events in Kelani River basin
(Department of Civil Engineering, University of Moratuwa, 2021-11) Chathuranga, GK; Fernando, WCDK; De Silva, PKC; Hettiarachchi, P
Floods, one of the major disasters in Sri Lanka occur not only due to a single daily rainfall but due to multiday rainfall events. Thus, to safeguard the properties, analysis of the multiday rainfall events is more relevant than analysis of one-day rainfall events. The objective of the research is to identify the temporal rainfall pattern in the Kelani River upper catchment (using Canyon, Castlereigh, Laxapana, Norton and Hatton - Meteorological stations) for conducting rainfall frequency analysis using data from the annual maximum (AMAX) series. The preparation of the data series is done by using the Block Maxima tool and the trend pattern is identified with the Mann-Kendall test. Then selected potential candidates for frequency analysis using the L-moment method and selected the best fit distribution by using the goodness of fit test. The final outcome is to identify the Extreme rainfall values for different return periods. According to Manne Kendal test results, all series have increasing trends but they are not significant, except for Norton PX3D which has a significant increasing trend. Hatton Kotagala PX3D has a decreasing trend that is not significant. For all AMAX series skewness is positive, In the kurtosis for all AMAX series except PX2D and PX3D in the Canyon, its tails are longer and wider, and often its central peak is higher and sharper(leptokurtic). For AMAX series PX2D and PX3D in the Canyon, its tails are shorter and narrower, and often its central peak is lower and broader (platykurtic). Gamma (G), Lognormal (LN), and Weibull (EV3) were selected as potential candidates for frequency analysis. From KS test results Gamma distribution fitted to 46% of the series, while Lognormal and Weibull fitted to 27% of the series. The maximum PX1D is 440 mm in 1989 at Laxapana and for the PX2D series, the maximum value is 831 mm in 1989 at Laxapana. It was observed that the maximum PX3D is 924.7 mm in 1989 at Laxapana. The average ratio between 3-day maxima to 1-day maxima is 2.1 and the ratio of 2-day to 1-day becomes 1.9. This finding greatly helps to estimate PX2D or PX3D in the context of engineering design when there is a lack of data. It is seen that there is an increasing trend at all stations except Hatton-Kotagala PX3D. However, a significant increasing trend was detected at Norton PX3D at a 5% level of significance. For all other stations, AMAX shows no significant trends. In general, it can be argued that the Kelani River Upper catchment has an increasing trend but is not significant for annual maximum rainfall series of one day, two days and three days at a 5% level of significance. The Gamma distribution is the best-fit distribution for most of the one-day annual maximum rainfall series. However, for two-day and three-day series all three distributions - Gamma distribution, Lognormal distribution, and Weibull distribution can be considered as equal. In low return periods such as 25 years and 50 years there is no such difference in return levels. However, for larger return periods, the discrepancy is higher. The accuracy and reliability of the results can be further improved by increasing the length of records and the number of gauging stations. If four- or fiveday events are considered in the analysis, a better idea about the extreme events can be obtained and how they combined with the flooding condition. These results can be used for flood mitigation projects, for statistical estimation of probable maximum precipitation, better models of risk and damage can be developed from multi-day extreme rainfall events and flooding.
item: Conference-Abstract
Effectiveness of it applications on consumer complaint for improvement of water supply: a case study with cluster analysis
(Department of Civil Engineering, 2023-09-27) Fernando, GDP; De Silva, PKC; Mallikarachchi, C; Hettiarachchi, P; Herath, S; Fernando, L
One of the most significant concerns of humankind has been the provision of adequate quantities and quality of water. Unfortunately, modern water distribution networks are complex and challenging to manage due to increased levels of urbanisation, varying consumer demands, and limited resources. Therefore, authorities must make critical decisions to solve problems associated with different phases and time frames of water distribution networks. Most of the management issues are challenging to solve using conventional problem-solving techniques. One of the versatile approaches for solving these management problems is to use customer complaints to develop optimisation techniques. National Water Supply & Drainage Board (NWSDB) receives various complaints about their services. This thesis presents a case study on the Biyagama water supply scheme, focusing on analysing leakage occurrence in the pipeline network. The study utilised a dataset collected by the National Water Supply and Drainage Board (NWSDB) for three years. Aim is to investigate the factors influencing leak occurrence in the Biyagama water supply scheme and develop a comprehensive understanding of pipe network vulnerability, with the objective of informing targeted maintenance strategies and improving the overall reliability and efficiency of the water supply system. The primary objective was to investigate the factors influencing leakages in the network and develop a comprehensive understanding of pipe network vulnerability. The research employed the Kmeans algorithm, implemented using the Python programming language, to conduct a cluster analysis of the dataset. The analysis incorporated factors, including age, inner diameter, and hydraulic parameters, such as pressure and velocity, to identify patterns and correlations associated with leak occurrence. The cluster analysis results revealed that age physical characteristics and hydraulic parameters alone were insufficient to explain the variations in leak frequency among the clusters. To account for this, additional factors were considered, including pipe material, installation quality, maintenance practices, temperature, soil condition, traffic load and environmental conditions. Incorporating hydraulic parameters, such as pressure and velocity, provided valuable insights into the relationship between fluid dynamics and leak vulnerability. High fluid velocities also correlated with leak occurrence. The findings emphasise the complexity of pipe network vulnerability and highlight the importance of considering multiple factors in assessing leakage occurrence. By gaining a comprehensive understanding of the factors influencing leaks, stakeholders can develop targeted maintenance strategies and improve the overall reliability and efficiency of the water supply system. This research contributes to the field of water supply management by providing insights into the vulnerabilities of pipe networks and the factors influencing leak occurrence. The findings can inform decision-making processes for infrastructure maintenance and support the development of sustainable water management strategies.
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: Conference-Abstract
Investigation on wave energy characteristics in South-Western coastline of Sri Lanka
(Department of Civil Engineering, University of Moratuwa, 2021-11) Thujanan, T; De Silva, PKC; Hettiarachchi, P
Ocean wave power is an abundant and promising renewable energy source with limited environmental impact and high energy density. The distribution of wave energy varies spatially and temporally, attributed to bathymetric and seasonal effects. Therefore, a proper wave energy resource assessment is required in order to find optimum sites which have higher wave energy potential so that the energy produced from Wave Energy Converters (WECs) can be maximised. The aim of this study was to investigate the wave power potential around the south-western coast of Sri Lanka and its spatio-temporal and directional distribution based on 5 years (1999 to 2003) of wave data simulated using SWAN (Simulating WAves Nearshore). The results of the analysis indicated that the annual mean wave power in the region is exceeding 10 kW/m while the possible monthly mean wave power values are higher than 5 kW/m throughout the year. A significant increase in the monthly mean wave power was observed from May to September months because of the influence of the tropical south-west monsoon. Sixteen study points were selected along the nearshore and offshore around the west coast (from Colombo to Beruwala) and south-west coast (from Beruwala to Matara) for a detailed assessment and numerical modelling was done using DELFT3D for high resolution nearshore bathymetry. The calculated annual and monthly mean wave power values at the selected nearshore points showed that the south-west coast has higher potential than the west coast except near Matara area. The temporal and directional variations were also assessed at selected points using statistical indices and wave power roses, and those revealed that the region has moderately stable wave power with narrow directionality. The annual electric power output that can be extracted from three commercially available wave energy converters; Oyster, Wave Star and Wave Dragon were estimated at all nearshore points using wave scatter diagrams and publicly available power matrices. Accordingly, the nearshore area from Galle to Weligama found to be most suitable for wave energy harvesting. Further, the performance of the selected devices was evaluated based on their capacity factors, and the Oyster and Wave Star converters were found to be most suited to the prevailing wave conditions in the region.
item: Thesis-Abstract
Tsunami hazards - assessment of exposure of Sri Lanka
De Silva, PKC; Ratnasooriya AHR; Samarawickrama SP
The coastal belts of several Indian Ocean countries including Indonesia, Sri Lanka, India and Thailand suffered massive loss of life and damage to property due to the tsunami unleashed by the great earthquake in the Sunda trench on 26 December 2004 which is now called as Indian Ocean Tsunami. In the context of Sri Lanka the extent of inundation and the associated damage varied significantly with the local near shore wave height, topography and the resistance offered to the overland flow and due to the lack of preparedness and unawareness about tsunamis, death toll and the damage was quite high around two third of the coastal zone of the country.As indicated by the Indian Ocean Tsunami and subsequent tsunami alerts in 2005 and 2007, it will be important to assess the risk of tsunamis for Sri Lanka from possible undersea earthquake zones around the country to mitigate the adverse effects of a future tsunami. That kind of study should assess the exposure of the country in terms of tsunami arrival time, nearshore wave height and extent of inundation for possible tsunami scenarios which could affect the country. Also according to the geographical location of the country, Sri Lanka is threatened by far field tsunamis with tsunami travel time of hours. So the ideal tsunami impact mitigation measure is an early warning and evacuation system. Therefore this study was focussed on assessing the exposure of Sri Lanka to potential tsunami events from Sunda trench and arranging the information from such assessment to be effectively utilized by an early warning system and evacuation system.
item: Conference-Abstract
Validating numerical model for bridge pier scour estimation through physical modelling – Case study of Kelanisiri Bridge
(Department of Civil Engineering, University of Moratuwa, 2024) Rathnayake, KKHM; Thembiliyagoda, A; De Silva, PKC; Pasindu, HR; Damruwan, H; Weerasinghe, P; Fernando, L; Rajapakse, C
Bridge scour is the erosion of sediment around bridge piers by flowing water, causing a significant risk to bridge stability and safety. Scour depth, the extent of sediment erosion around bridge piers or other structures caused by flowing water, is a critical parameter in bridge engineering. Generally, there are three types of scour phenomena that impact the performance and safety of bridges as local scour, contraction scour, and degradational scour. Understanding these are essential for identifying and reducing any dangers to the stability and safety of bridges. This research aims to investigate the scouring phenomenon around the bridge piers of the Kelanisiri Bridge in Sri Lanka, understand its mechanisms, develop predictive models, and propose effective mitigation measures. The Kelanisiri bridge spans 134 m and is 10.4 m wide, has two cylindrical piers with a diameter of 2.5 m and has undergone scouring around piers, posing a severe danger to its stability. Also, this aims to contribute to the creation of sustainable solutions by examining the scouring processes and assessing the effects of variables like sediment types, flow velocities, and hydrological conditions through a combination of field investigations, laboratory experiments, and numerical modelling techniques. Further, this research will help to improve Sri Lanka's transportation infrastructure by ensuring the country's road network remains resilient and connected in the face of changing hydraulic conditions and sediment transport processes in river systems. In this research, a laboratory scale physical model is developed to validate the results obtained from a numerical model developed using HEC-RAS software. The physical model replicates the bridge pier and surrounding riverbed at a scaled-down size, using similar materials. This allows for direct visualization of the scour process and the collection of detailed scour depth data at various locations around the pier. In the numerical model, HEC-RAS has capability to incorporate sediment transport equations, conduct extensive flow pattern studies, simulate complex river geometries, and offer a broad array of analytical tools. Comparing the scour depths obtained in the physical model with the predictions from the numerical model allows for an assessment of the validity and limitations of the numerical simulations. The performance of the HEC-RAS model in replicating the physical model's scour depth measurements was assessed using R-squared (R²) and Root Mean Squared Error (RMSE). R², ranging from 0 to 1, indicates the proportion of variance in the observed scour depths explained by the model's predictions. A good model exhibits both a high R² (strong correlation) and a low RMSE. The outcomes of the physical model comply well with the HEC-RAS numerical model results, with R2 value of 0.87 and RMSE value of 0.12. Therefore, the accuracy of the numerical model, which had been designed to predict scour depth for the bridge piers at Kelanisiri bridge can be validated through this laboratory-scale experimentation. Finally, these discoveries will be critical in assuring the safety and durability of bridge constructions in Sri Lanka