Research Papers - Department of Civil Engineering

Permanent URI for this collectionhttps://rda.sliit.lk/handle/123456789/598

Browse

Filters

2007 - 200942010 - 201926

Advanced Search

Filter by

Settings

Author: search.filters.author.Rathnayake, U. SEnd date: 2019

Search Results

Now showing 1 - 10 of 30
  • Thumbnail Image
    PublicationOpen Access
    Entrance zone effect on the sediment trapping efficiency in desilting tanks of run-of-river type mini-hydropower plants
    (The University of Peradeniya, Peradeniya, Sri Lanka, 2007-11-30) Rathnayake, U. S; Harishchandra, M. R. T. S; Weerakoon, S. B
    Development of run-of-river type minihydropower plants is receiving increased attention in Sri Lanka at present owing to the incentives announced for developers of renewable power generation projects during the last decade by the Sri Lankan government. The sources for most of the run-of-river type mini hydropower plants are mountainous streams where the discharges experience significant seasonal variation with frequent flash floods. The catchments of these streams are generally steep and face an increasing trend of soil erosion due to cultivation and other human activities. Therefore, the stream flows carry high sediment loads during seasonal floods. This sediment-laden flow enters the headrace canals feeding water to the turbines of the rninhydropower plants. Sediment in the water passing through the turbines with high velocity erode the contact surfaces of turbine components. The erosion of turbine components leads to a drop in hydraulic efficiency and to a high maintenance cost of the turbines. Removal of sand carried with the flow in the headrace canals of run-of-river mini hydropower plants is therefore an important issue for the developers to reduce the maintenance cost of the turbines (Singal and Ranendra, 2006). Introduction of a de-silting tank in series with the headrace canal is one of the commonly used techniques for this purpose. De-silting tanks are designed as settling basins to settle sediment greater than a targeted size (Janssen, 2004). The shape and the size of the de-silting tank are major factors affecting the sand trapping efficiency of the desilting tank. Several empirical and semiempirical relations for the efficiency of …
  • Thumbnail Image
    PublicationOpen Access
    Experimental investigation of hyporheic interactions
    (2010) Rathnayake, U. S; Izumi, N
    Research on hyporheic interactions is not new to the present world, but most of the previous research is in the environmental and ecological points of view. This study was to understand the hyporheic interactions by means of engineering perspectives. Several experiments were carried out at laboratory scale to identify the relationships between important non-dimensional river parameters and non-dimensional interaction parameters. Results can be concluded to show some clear relationships among the non-dimensional parameters.
  • Thumbnail Image
    PublicationOpen Access
    Impact of urbanization on earth resources in suburbs of Colombo, Sri Lanka
    (NSF: Colombo, 2019) Rathnayake, U. S
    Climate change is believed to be a critical issue and there is enough evidence to identify the impact of climate change. Sri Lanka is expected to be one of the most affected countries from adverse impact of climate change. Various climatic models propose a rise of rainfall intensity to south Asian region while the number of rainy days are to be reduced. Therefore, the necessity is raised to find the clear trends in climatic factors in the region. However, a very few research work was carried out to see the climatic changes over the last few decades in Sri Lanka. Temporal variation of precipitation (rainfall) can be a good indicator to identify the trends in climate. In addition, these rainfall variations are used in many engineering aspects, including design of massive civil engineering structures like dams, design of water supply networks, etc. Furthermore, the rainfall variations are not only important in engineering aspects but also heavily in agriculture. Therefore, this research work targets to find the temporal variations of rainfall n Sri Lanka and then, to project the results to the available water resources.
  • Thumbnail Image
    PublicationOpen Access
    Theoretical analysis for the interaction between the river flow and the seepage flow
    (Proceedings of the 6th WSEAS International Conference on FLUID MECHANICS, 2009) Rathnayake, U. S; Izumi, N
    Many previous studies have been carried on the interaction between river flow and the seepage flow in the environmental point of view, but these hardly touch on the boundary conditions or the limitations for the interactions. The subsurface layer below the river is known as the hyporheic layer and it is a saturated band of sediment that surrounds river flow and forms a linkage between the river and the aquifer. The large velocity difference between the river flow layer and the seepage flow layer causes the instability of the flows. Due to this flow instability, a reciprocating flow motion is generated between the hyporheic layer and the above. Linear stability analysis technique is used to understand the stability of the natural flows in rivers as well as the flows occurred in the air by many researchers. In this study a linear stability analysis is carried out to presents the interaction between the river flow and seepage flow. Reynolds averaged Navier-Stokes equations and Brinkman-Forchheimer equations are used in order to formulate the river flow and seepage flow interaction. The open channel flow is analyzed by mixing length turbulent model and Spectral collocation method incorporated with the Chebyshev polynomials are used to perform the numerical solution of the perturbed equations. Instability diagrams are discussed with several slopes of the layers against the dimensionless particle diameter and wave numbers. It has been noted that the instability occurs even in the range of small dimensionless particle diameter with relatively high wave numbers if there is a seepage layer beneath the flow and the instability region increases with the slope when the wave numbers are at small values.
  • Thumbnail Image
    PublicationOpen Access
    Flood Modelling in Waidina Tributary, Fiji Islands
    (2015 Department of Civil and Environmental Engineering, University of Ruhuna3rd International Symposium on Advances in Civil and Environmental Engineering, 2015) Rathnayake, U. S; Arachchi, S. M. A
    Rewa River is the widest river and the second longest river in Fiji Islands. It is in the islands of Viti Levu. The river is 145 km in length and starts from the highest peak of the island, Tomanivi. Rewa River experiences frequent floods. However, a detailed flood model for Rewa River is still to be tabled. This paper briefs the flood modeling of part of Waidina tributary of the Rewa River. US Army Corps Engineers HEC-RAS hydraulic model is being successfully applied to the Rewa River and initial results are drafted for the Waidina tributary. These results are promising; however, a completed flood model should be developed for sound conclusions. Inundation top widths due to a random flood were presented. These inundations can effectively be used to inform the residents in the vulnerable areas in a flood event. In addition, the final expected results can be used for the flood protection structural measures.
  • Thumbnail Image
    PublicationOpen Access
    Hydrological assessment of flow in Uma Oya, Sri Lanka
    (Faculty of Engineering, Sri Lanka Institute of Information Technology, 2015-01-29) Rathnayake, U. S
    A current meter is usually used in river flow measurements. However, if someone is interested in obtaining the temporal variation of a particular river, it may not be the easiest method in the world to use a current meter (i.e. daily) to measure the flow rate. In such events, the stage measurements can be taken and then, they can be converted to the flow rates (USGS, 2014). One can use the stage-discharge relationship to find the corresponding flow rate (Mortuza et al., 2011; Raj and Azeez, 2009; Gupta and Chakrapani, 2005). However, this method still requires some flow measurements to produce the stage-discharge relationship. Therefore, a current meter should be there to measure the velocities and then, to calculate the flow rates. In case of absence of a current meter, one has to think another way of obtaining the flow hydrograph. This paper presents a simple approach in obtaining the flow hydrograph for a river in Sri Lanka: Uma Oya. Uma Oya catchment is being modeled and this study shows some preliminary results. The detailed flow hydrograph for Uma Oya for a longer period is being developed for the frequency analysis. The developed flow hydrograph is being used to model the Uma Oya catchment in Sri Lanka
  • Thumbnail Image
    PublicationOpen Access
    Sustainable stormwater management system: a conceptual design model for SLIIT, malabe campus, Sri Lanka
    (Faculty of Engineering, Sri Lanka Institute of Information Technology, 2016) Khaniya, B; Wanniarachchi, S. S; Rathnayake, U. S
    In recent years, significant attention has been given to the utilization of water and its components. Management of the wastewater including run-off to maintain a balanced eco-system has been an irony issue mostly in urban areas. Conventional water management systems such as reducing peak flow rate, sewer systems, end of pipe mitigation measures do not tend to fulfill the tortuous developmental plan of growing cities. It is therefore, necessary to use the principle management concepts such as best management practices (BMPs), low impact developments (LIDs) focusing on micro-management design concepts to intensify the existing hydrological cycle. Structural practices such as perforated infiltration trench along with bio-retention pond is thought to control the storm water at Sri Lanka Institute of Information Technology (SLIIT) premises based on the biophysical, hydrological and ecological ascribes of the landscape. This was identified as a critical issue to the well-being of the students during the rainy periods. Impervious layers introduced in aesthetic purposes have reduced the infiltration and then, increase the temporary flooding / pooling of these impervious surfaces. Post-development water management requires multi-disciplinary understanding of watershed along with identification of predevelopment functions and their constraints. Therefore, parameters of soil properties like permeability, grain size, and other parameters like soil profile analysis, water quality analysis, water table depth, soil moisture condition and trench geometry based on terrain at two different sites were analyzed. Field tests were performed to find infiltration rates to compute the performance of the trench and to determine the storage volume based on rainfall events. Thus, this paper imparts colors upon an affordable, pragmatic and long-term solution to meet the need of modern water management at SLIIT. An infiltration trench network is being proposed to overcome the flooding / pooling problems in SLIIT premises and the proposal is being presented to the management of the institution.
  • Thumbnail Image
    PublicationOpen Access
    Rainfall analysis in Uma Oya basin, Sri Lanka
    (Faculty of Engineering, Sri Lanka Institute of Information Technology, 2016) Senadeera, D; Wanniarachchi, S; Rathnayake, U. S
    Climate change is believed to be a critical issue and there is enough evidence to identify the impact of climate change. Sri Lanka is expected to be one of the most affected countries from adverse impact of climate change. Various climatic models propose a rise of rainfall intensity to south Asian region while the number of rainy days are to be reduced. Therefore, the necessity is raised to find the clear trends in climatic factors in the region. However, a very few research work was carried out to see the climatic changes over the last few decades in Sri Lanka. Temporal variation of precipitation (rainfall) can be a good indicator to identify the trends in climate. In addition, these rainfall variations are used in many engineering aspects, including design of massive civil engineering structures like dams, design of water supply networks, etc. Furthermore, the rainfall variations are not only important in engineering aspects but also heavily in agriculture. Therefore, this research paper presents an analysis of temporal variation of rainfall in Uma Oya basin, Sri Lanka. Initial results show some interesting trends in rainfall over a period of 24 years. Furthermore, research is being conducted using advanced statistical data analysis techniques to present comprehensive trends in rainfall in Uma Oya basin
  • Thumbnail Image
    PublicationOpen Access
    Urbanization and initial groundwater quality investigation in Malabe, Sri Lanka
    (https://www.tci-thaijo.org/index.php/easr/article/view/91589, 2018-06) Rajapakshe, A; Rathnayake, U. S
    Malabe, an eastern suburb of the capitalcity of Colombo, is one of the most rapidly urbanized and industrialized areasin Sri Lanka. Groundwater is avaluable resource inMalabe and itis being polluted. Malabe is located in a wet climatic zone with alateritic aquifer thatnormally contains water with avery low pH thatcan cause quality problems. Our objective was to investigate and analyzethe Malabe groundwater quality to understand the characteristics of significant parameters and their correlation so that policy planning can be correctly done. Groundwater samples from 16 water wells were collected and evaluated for eightphysicochemical parameters,i.e.,pH, turbidity, electrical conductivity (EC), color, nitrate (NO3), nitrite (NO2), sulfate (SO4), and phosphate (PO4). Two biological parameters were also determined for four wells. The essence of this finding is that the groundwater is very acidic, has a very low EC, but high coliform counts. Multivariable statistics of the data were performed usingPearson’scorrelation and principal components analysis (PCA) using the Princom package intheR statistical package. The first four principal components (PCs) explained 79.8 % of the total observed variance inthe data. The most significant parametersfrom the first principalcomponent, PC1, were the positive correlationsof turbidity andPO4, and negative correlationsof EC andNO3. Asignificant positive loading of pH with a negative loading of SO4was illustrated in PC2. These findings were similar to the correlation results. We concludesthat the high acidity of the groundwater is primarily caused by industrial waste. The groundwater pollution of the Malabe area was not cause by inorganic fertilizer but by anthropogenic waste runoff. Our finding is crucial for groundwater quality management inthe study area.
  • Thumbnail Image
    PublicationOpen Access
    Flood modeling in the Mahaweli River reach from Kothmale to Polgolla
    (University of Peradeniya, 2007) Rathnayake, U. S; Weerakoon, S. B; Nandalal, K. D. W; Rathnayake, U
    The occurrence of floods and inundation of the low lands adjacent to the Mahaweli River reach from Gampola to Polgolla were very frequent prior to the Kotmale reservoir project in mid 1980s. However, during last two decades with the construction of the Kotmale dam, the regulation of flow by the reservoir has reduced the inundation risk of these lands, which were vulnerable to frequent flooding. As a result, these lands are developed at an increasing rate and more people have started to live in them. This fact gives an alarming signal to the authorities, as the damage that might be caused due to an extreme flood event could be significant. It is therefore of paramount importance that comprehensive flood modeling and inundation analysis of the Mahaweli River reach between Kotmale and Polgolla is carried out. This paper presents the flood modeling and inundation analysis in the Mahaweli river reach from the Kotmale dam to Polgolla barrage using the HECRAS model. The HECRAS model was set up for the river reach using the river cross-sections at 200 m intervals from Kotmale dam to Polgolla barrage. The model was applied to estimate the water stages along the river reach for the floods of different return periods. Though the Kotmale reservoir acts as a flood control reservoir for floods of medium return periods, it becomes ineffective to reduce the flood levels in the downstream flood plains due to floods of high return periods when it has to release high discharge. Inundation areas in the downstream of the dam due to several flood discharges are presented.