Browsing by Author "Azamathulla, H. M"

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Open Access
Comparing Combined 1D/2D and 2D Hydraulic Simulations Using High-Resolution Topographic Data: Examples from Sri Lanka—Lower Kelani River Basin
(MDPi, 2022-02-17) Samarasinghe, J. T; Basnayaka, V; Gunathilake, M. B; Azamathulla, H. M; Rathnayake, U
The application of numerical models to understand the behavioural pattern of a flood is widely found in the literature. However, the selection of an appropriate hydraulic model is highly essential to conduct reliable predictions. Predicting flood discharges and inundation extents are the two most important outcomes of flood simulations to stakeholders. Precise topographical data and channel geometries along a suitable hydraulic model are required to accurately predict floods. Onedimensional (1D) hydraulic models are now replaced by two-dimensional (2D) or combined 1D/2D models for higher performances. The Hydraulic Engineering Centre’s River Analysis System (HECRAS) has been widely used in all three forms for predicting flood characteristics. However, comparison studies among the 1D, 2D to 1D/2D models are limited in the literature to identify the better/best approach. Therefore, this research was carried out to identify the better approach using an example case study of the Kelani River basin in Sri Lanka. Two flood events (in 2016 and 2018) were separately simulated and tested for their accuracy using observed inundations and satellite-based inundations. It was found that the combined 1D/2D HEC-RAS hydraulic model outperforms other models for the prediction of flows and inundation for both flood events. Therefore, the combined model can be concluded as the better hydraulic model to predict flood characteristics of the Kelani River basin in Sri Lanka. With more flood studies, the conclusions can be more generalized.
Open Access
Computation of Time of Concentration Based on Two-Dimensional Hydraulic Simulation
(MDPI, 2022-10-07) Zolghadr, M; Rafiee, M.R; Esmaeilmanesh, F; Fathi, A; Tripathi, R.P; Rathnayake, U; Gunakala, S. R; Azamathulla, H. M
: Time of concentration (TC) is a parameter in runoff estimation, used to study and design different types of projects in watersheds. Any error in TC calculation leads to an inaccurate estimation of the design flow, which can lead to over-sizing or under-sizing of designed facilities that can have great economic and environmental consequences. Therefore, choosing the correct method to estimate TC is of great importance. Due to the diversity of estimation methods in the literature, the obtained TC values are different. This study aims to present a new method to calculate TC, based on its main concept, i.e., the time required for a water parcel to reach its outlet from the farthest hydrological point of a watershed. A two-dimensional hydraulic simulation was used to model the water parcel travel. A watershed was selected as a case study, and its time of concentration was determined by salt solution tracing. The field measurement results were used for calibration of the numerical simulation model. Meanwhile, 31 empirical relations in the literature were reviewed to determine the most accurate ones. Estimated TC values were compared with the measured ones, and the relative error percentage was used to evaluate the accuracy of the result. In the empirical TC methods, the maximum error was above 300%, and the minimum error was 6.7% for the field studied area. The relative errors of hydraulic simulation outputs were between 3 and 27%. The results showed that only three empirical methods, namely Simas and Hawkins, SCSlag, and Yen and Chow, had the least errors respectively equal to 6.7%, 8.660%, and 13.5%, which can be recommended for the studied area and those with similar hydrological characteristics. On the other hand, hydraulic simulation is also introduced as an efficient method to determine TC which can be used in any desired watershed.
Open Access
Data exploration on the factors associated with cost overrun on social housing projects in Trinidad and Tobago
(Elsevier Ltd, 2024-02) Chadee, A. A; Allis, C; Rathnayake, U; Martin, H; Azamathulla, H. M
This data article explores the factors that contribute to cost overrun on public sector projects within Trinidad and Tobago. The data was obtained through literature research, and structured questionnaires, designed using open-ended questions and the Likert scale. The responses were gathered from project actors and decision-makers within the public and private construction industry, mainly, project managers, contractors, engineers, architects, and consultants. The dataset was analysed using frequency, simple percentage, mean, risk impact, and fuzzy logic via the fuzzy synthetic evaluation method (FSE). The significance of the analysed data is to determine the critical root causes of cost overrun which affect public sector infrastructure development projects (PSIDPs), from being completed on time and within budget. The dataset is most useful to project and construction management professionals and academia, to provide additional insight into the understanding of the leading factors associated with cost overrun and the critical group in which they occur (political factors). Such understanding can encourage greater decisions under uncertainty and complexity, thus accounting for and reducing cost overrun on public sector projects. © 2023
Open Access
Environmental and Social Impacts of Mini-hydropower Plants—A Case Study from Sri Lanka
(DAVID PUBLISHING, 2018-03-15) Senarath, P.; Khaniya, B; Baduge, N; Azamathulla, H. M; Rathnayake, U. S
This research study was conducted to review the environmental and social impact of mini hydropower plants (run-of-the-river type) by selecting Denawaka Ganga mini hydropower plant, which is located in Ratnapura district, Sri Lanka. Field visits and discussions among the authors, authorities and the residents were carried out. Then, the environmental and social impacts were scientifically analysed using regulation degree (RD) and environmental impact value (EIV) scores. It was found out that the Denawaka Ganga mini hydropower plant has induced some environmental concerns; however, significant positive social impact to the society. This is in addition to the green energy generation. Therefore, it can be concluded herein that the Denawaka Ganga mini hydropower is an asset to the country, Sri Lanka.
Open Access
Evaluation of Future Streamflow in the Upper Part of the Nilwala River Basin (Sri Lanka) under Climate Change
(MDPI, 2022-03-16) Chathuranika, I. M; Gunathilake, M. B; Azamathulla, H. M; Rathnayake, U
Climate change is a serious and complex crisis that impacts humankind in different ways. It affects the availability of water resources, especially in the tropical regions of South Asia to a greater extent. However, the impact of climate change on water resources in Sri Lanka has been the least explored. Noteworthy, this is the first study in Sri Lanka that attempts to evaluate the impact of climate change in streamflow in a watershed located in the southern coastal belt of the island. The objective of this paper is to evaluate the climate change impact on streamflow of the Upper Nilwala River Basin (UNRB), Sri Lanka. In this study, the bias-corrected rainfall data from three Regional Climate Models (RCMs) under two Representative Concentration Pathways (RCPs): RCP4.5 and RCP8.5 were fed into the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) model to obtain future streamflow. Bias correction of future rainfall data in the Nilwala River Basin (NRB) was conducted using the Linear Scaling Method (LSM). Future precipitation was projected under three timelines: 2020s (2021–2047), 2050s (2048–2073), and 2080s (2074–2099) and was compared against the baseline period from 1980 to 2020. The ensemble mean annual precipitation in the NRB is expected to rise by 3.63%, 16.49%, and 12.82% under the RCP 4.5 emission scenario during the 2020s, 2050s, and 2080s, and 4.26%, 8.94%, and 18.04% under RCP 8.5 emission scenario during 2020s, 2050s and 2080s, respectively. The future annual streamflow of the UNRB is projected to increase by 59.30% and 65.79% under the ensemble RCP4.5 and RCP8.5 climate scenarios, respectively, when compared to the baseline scenario. In addition, the seasonal flows are also expected to increase for both RCPs for all seasons with an exception during the southwest monsoon season in the 2015–2042 period under the RCP4.5 emission scenario. In general, the results of the present study demonstrate that climate and streamflow of the NRB are expected to experience changes when compared to current climatic conditions. The results of the present study will be of major importance for river basin planners and government agencies to develop sustainable water management strategies and adaptation options to offset the negative impacts of future changes in climate.
Open Access
Gene expression programming and artificial neural network to estimate atmospheric temperature in Tabuk, Saudi Arabia
(SpringerLink & King Abdulaziz City for Science and Technology, 2018-09-19) Azamathulla, H. M; Rathnayake, U. S; Shatnawi, A
Climate change is not a myth. There is enough evidence to showcase the impact of climate change. Town planners and authorities are looking for potential models to predict the climatic factors in advance. Being an agricultural area in Saudi Arabia, Tabuk region gets greater interest in developing such a model to predict the atmospheric temperature.Therefore, this paper presents two diferent studies based on artifcial neural networks (ANNs) and gene expression programming (GEP) to predict the atmospheric temperature in Tabuk. Atmospheric pressure, rainfall, relative humidity and wind speed are used as the input variables in the developed models. Multilayer perceptron neural network model (ANN model), which is high in precession in producing results, is selected for this study. The GEP model that is based on evolutionary algorithms also produces highly accurate results in nonlinear models. However, the results show that the GEP model outperforms the ANN model in predicting atmospheric temperature in Tabuk region. The developed GEP-based model can be used by the town and country planers and agricultural personals
Embargo
Impact of climate variability on hydropower generation: A case study from Sri Lanka
(Taylor & Francis Group, 2018-06-18) Khaniya, B.; Priyantha, H. G; Baduge, N; Azamathulla, H. M; Rathnayake, U. S
Hydropower accounts for 16.4% of world’s electricity demand. The key element in hydropower generation is the runoff and this runoff totally depends on the precipitation. However, the future climate is predicted to be debatable and can severely affect the water resources around the world. Therefore, a critical question to answer by the research community is, what would be the impact of climate change/variability on hydropower development? Hence, this paper aims to study the impingement of climate change on hydropower generation for Denawaka Ganga mini-hydropower located in Ratnapura district, Sri Lanka. Multi-year rainfall trend analysis for 30 years along with power generation trend study for 6 years have been carried out to evaluate the performance of the hydropower station under possible shifting precipitation pattern. Mann–Kendall test and Sen’s slope estimator tests were used to culminate the trend analysis. Seasonal and monthly trend analysis did not render negative trends (except one rain gauge) in rainfall. However, positive rainfall trends were found in several rain gauging stations for several months. Power generation trend study showcased a decreasing trend in electricity generation for January and November. Nevertheless, the results elucidate that the catchment area is not under an intense threat due to the climate variability.
Open Access
Influence of Crumb Rubber and Coconut Coir on Strength and Durability Characteristics of Interlocking Paving Blocks
(MDPI, 2022-07-13) Gamage, S; Palitha, S; Meddage, D. P. P; Mendis, S; Azamathulla, H. M; Rathnayake, U
Interlocking Paving Blocks (IPB) are, nowadays, a widely used construction material. As a result of the surge in demand for IPBs, alternative materials have been investigated to be used for IPBs. This study investigated the strength and durability characteristics (compressive strength, split tensile strength, density, water absorption, skid resistance, and abrasion resistance) of IPBs in the presence of (waste materials) crumb rubber (CR) and coconut coir fibers (CCF). Both compressive and split tensile strength increased in the presence of CCF to a certain extent. CR-based IPBs showcased an increase in skid resistance that satisfied both SLS 1425 and BS EN 1338 specifications. Abrasion depths of CR-based and CCF-based samples show a comparable increase in values when the respective fraction (CR or CCF) increases. Therefore, this research fills the knowledge gap, highlighting the importance of incorporating waste materials (CR and CCF) for the IPB industry rather than open dumping.
Embargo
Two consecutive storms and optimal control of urban sewer networks to minimize the pollution load of combined sewer systems
(Springer International Publishing, 2017-03-01) Rathnayake, U. S; Azamathulla, H. M
Combined sewer overflows (CSOs) are a burdened environmental issue. Structural measures are not the best solution to cope with or to minimize these adverse impacts from CSOs. Non-structural measures, if possible to implement, would be the best solution in sustainable development. Controlling of existing urban sewer networks is a potential non-structural measure to minimize the adverse impacts of CSOs. Several algorithms to control urban sewer networks are in literature; however, there is little literature in minimizing the environmental impacts from CSOs. Rathnayake and Tanyimboh (Management 29:2715–2273, 2015) have successfully developed a control algorithm to minimize the environmental impacts or to enhance the quality of receiving water in an event of CSOs. However, this control algorithm is based on single-peaked runoff hydrographs. Not only for the research in control of urban sewer networks, but also in most other researches, single-peaked runoff hydrographs are generally applied. This is due to the modeling simplicity. However, in real world, these conditions may not be applicable. It is very common to have a second peak after the first peak in the hydrograph. The second peak may or may not be high as the first; however, it is important to consider these peak flows, when it comes to design and control of combined sewer systems. Therefore, this reach was carried out to improve Rathnayake and Tanyimboh’s optimal control algorithm (2015) for two consecutive storms. Runoff hydrographs due to two consecutive storms and pollutographs were developed in improving the Rathnayake and Tanyimboh’s control algorithm. Results manifest the benefits of using multi-objective optimization in controlling combined sewer networks under two consecutive storms where many sets of feasible control settings can be obtained. A desired control settings can be implemented to the sewer system according to the available resources.