Master of Engineering in Water Resources Engineering & Management

Permanent URI for this collectionhttp://192.248.9.226/handle/123/16125

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item: Thesis-Full-text
Identification of water management concerns in irrigation - study of water issue practice at rajangana reservoir, sri lanka
Chemjong, H; Wijesekera, NTS
Sri Lankan paddy production satisfies only 90% of total demand and 10% is being imported from other countries. On one hand, the cultivable land is narrowing day by day because of the urbanization. On the other hand, Climate change factors, food requirements for increased population and present level of yields demonstrate the need to significantly increase the production in support of future food requirements. Average rice yield of Sri Lanka is 4.5 MT/Ha but the potential is between 7 to 12 MT/Ha. In most parts of Sri Lanka, water is the critical factor for cultivation. Using the appropriate amount saves water for more land to be cultivated. Hence efficient water management is very important to increase food production. Irrigation water distribution is usually carried out with the help of Guidelines. Therefore in a operational scheme, it is possible to compare a canal water issues and planned water issues to capture the status of water management for necessary improvements The present work is a study of irrigation water issue practice in Rajangana Irrigation Scheme at Anuradhapura which is located in the North Central Province of Sri Lanka Technical Guideline of Irrigation Department is the document used for irrigation system management in Sri Lanka. Using water issues and other data for the period of 2008-2013 the present work compared weekly water requirements with actual water issues. Initially using field data computed the water requirements as recommended by the Guideline was computed using field data and 75% probability rainfall. Then the quantities were calculated to identify the modifications to the plan with the availability of actual rainfall data during operations. These two data sets was named "Recommended Irrigation Plan" and "Anticipated water use" respectively. They were compared with each other and also with irrigation plans that had been prepared by Rajangana Irrigation Scheme, and with the water issues at the sluice gate. The study compared the case of Left Bank gravity fed irrigation area which covers an approximate 2500 Ha area with 39 Km tertiary canal network. The Rajangana project area is cultivated mainly with paddy during the two main rainy seasons namely "Maha" and "Yala". Water issue model for the study comparisons was developed using a weekly time resolution. Comparison of actual water use with the quantities which were computed by following Irrigation Department Guidelines, disclosed a significant over issue in Maha and Yala seasons amounting to 63% and 52% respectively. In the case of making the adjustments to the plan with the receipt of actual rainfall, then a further reduction of water issue by 35% and 8% in Maha and Yala respectively could have been possible. It was revealed that though computations were based on the same Irrigation Department Guideline recommendation, average Maha and Yala water requirements land increased by 25% and 75% respectively in the Rajangana Irrigation Division plan when compared with the plan developed by the study. Average actual water use during the initial crop growth stage was 4 times higher than the guideline recommended plan and taking account of rainfall received at Rajangana Scheme. In case of other growth stages too, the average increase of usage between 1.5 to 2.4 times reflected a poor rainfall accounting in practice. Evaluation revealed the need of gauge network, a spatially distributed performance monitoring system and a critical evaluation of the present Guideline in order to suitably manage the water utilization in the Rajangana Left bank irrigation scheme. It has been pointed out that better use of water in the scheme would enable better chances of serving other water deprived areas.
item: Thesis-Full-text
Development of a rainfall runoff model for Kalu ganga basin of Sri Lanka using HEC-HMS model
Jayadeera, PM; Wijesekera, NTS
Water resources management and flood management in a watershed needs identification of the runoff hydrographs and their relationship with the watershed parameters. Sri Lankan Engineering guidelines or literature in Sri Lankan studies do not provide recommendations for a Hydrologic Model or a modeling methodology guideline for a water manager to use for application purposes. In order to fill the gap in knowledge, this research developed a model using Hydrologic Engineering Centre - Hydrologic Modeling System (HEC-HMS) through a case study application on Ellagawa watershed in Kalu Ganga basin of Sri Lanka. Eight year daily rainfall data from 2006 to 2014 for five rain gauging stations scattered in the Ellagawa watershed with daily streamflow data in Ratnapura and Ellagawa river gauging stations together with eight year monthly evaporation data of Ratnapura station for the same period were used for this study. After a critical evaluation of HEC HMS options, one layer Deficit and Constant loss method in HEC HMS, was used as precipitation loss model which accounts for the soil moisture content in the continuous model. Soil Conservation Service (SCS) unit hydrograph method and recession method were selected for simulation of direct runoff and baseflow respectively. The evaluation identified Muskingam model as the suitable routing model. Model calibration was done using data from 2006 to 2010 and the calibrated model was verified using the dataset from 2010 to 2014. Both automated parameter optimization in HEC HMS and manual calibration were used in model calibration. The study demonstrates a systematic methodology for the selection of a search algorithm and the appropriate objective function was incorporated. The univariate gradient search method was selected to optimize the parameters by minimizing the Sum of Absolute Residual objective function. Manual calibration was carried out using Mean Ratio of Absolute Error (MRAE) as the objective function. In addition, another two statistical goodness of fit measures such as percent error in volume, and Nash-Sutcliff model efficiency were also checked as an observation. Evaluation shows that the value of MRAE for Ellagawa and Ratnapura catchments were 0.5406 and 0.5226 respectively during calibration. The MRAE values for Ellagawa and Ratnapura catchments during model verification were 0.6070 and 0.7732 respectively. Model estimated intermediate flows between 17 m3/s and 31 m3/s, with a very high accuracy of MRAE 0.326 and flows between 31 m3/s and 143 m3/s, estimations was acceptable at a MRAE of 0.5279. Model estimated high flows greater than 143m3/s with a very high accuracy of MRAE 0.3244, while the low flows which was less than 17 m3/s, could not be estimated very well. But the magnitude of lowflow errors for both catchments were only 1% of average annual streamflow of Ellagawa and Ratnapura and therefore this model can be used satisfactorily for water resources management. The model matching of time of peakflow occurrence was at an accuracy of 60% while the peak flow magnitude accuracy was 75%. Therefore, this model is acceptable to use in flood management.
item: Thesis-Full-text
Untitled
(2015-10-19) Jaman, M; Rajapakse, RLHL
All over the world, masses of human beings consume water for both potable and non-potable uses. While access to safe drinking water is explicitly acknowledged as a basic human need, water has an economical value in today’s world market. The water crisis and impending climate change impacts highlight the immediate need for adopting alternative solutions to relieve the pressure on conventional water sources and Rain Water Harvesting (RWH) is ascribed as one of the most sustainable, low cost solutions equally applicable to both the urban and rural water management systems. In consideration of ever growing need for water conservation and as a measure in addressing the future issues of sustainable water management, the Government of Sri Lanka (GOSL) has recently implemented policies, rules and regulations to promote rainwater harvesting and one of the technologies recommended by the government is the Roof-top Rainwater Harvesting Systems (RRWHS). However, the initial investment cost for the storage tank is relatively high for rural communities in need and lack of information on tank size selection, cost recovery time, etc., hinder the popularizing and adopting of RRWHS among both rural and urban communities. In this study, an evaluation and assessment of presently existing RRWH practices in Sri Lanka have been undertaken in an attempt to identify the probable reasons that hinder popularising of RRWH among both communities, while a special consideration is given to the design aspects lacking concerns of cost, making RRWHS unaffordable especially to rural communities in need. To investigate the design considerations under the constraints of economical and reliability aspects, the design of storage tank, conveyance system and quality system of RRWHS are considered. Based on the findings of the present study, the estimation of the storage tank size is recommended to be achieved by daily water balance equation method and the excel worksheet model developed in this study was found to be more effective than the mass balance, analytical, and sequent peak algorithm methods presently in practice. The conveyance system is recommended to be designed based on updated rainfall intensity values (from updated IDF curves) and the quality of water harvested can be improved by incorporating a fixed volume first flush diverter. The time for cost recovery estimated based on present tariff for pipe-borne water and average household water use has been recognized as a fact to justify use of RRWH in urban setups, further to other indirect benefits. The recommendations for the best methodologies and possible further improvements are proposed based on the benefits of cost reduction estimated according to the present water consumption rate using present water tariff and calculating the cost recovery period for the RRWH systems.
item: Thesis-Abstract
Event based modelling of streamflow for reliable flood mitigation and drainage infrastructure designs using snyder’s synthetic unit hydrograph method - a case study of Karasnagala watershed in the Attanagalu oya of Sri Lanka
(2015-10-19) Thapa, G; Wijesekera, NTS
The main purpose of water resources development is to enhance the water availability and equitable distribution among the stakeholders. Most of the infrastructure development structures are seen in the ungauged watersheds and as a country looking forward for development activities requires accurate estimations. Although the regional parameters provide a simple and clear indication, only limited work could be found on event based or watershed characteristics based or watershed characteristic based runoff coefficient estimates. In this study, daily rainfall data is applied to Karasnagala river basin (52.58 km2), Sri Lanka to simulate discharge. The study used event based modelling and Concave method baseflow separation technique to derive the Snyder’s Unit Hydrograph parameters. A minimum Inter-event Time criterion was applied to determine the independent events for modelling. The model calibration was done with 30 events and 30 events were used for model verification. An average value of Ct and Cp from 30 optimised events during calibration was 3.75 and 0.38 respectively. Model performance showed that Mean Ratio of Absolute Error (MRAE) and Ratio of Absolute Error to Mean (RAEM) were 0.20 and 0.21 respectively. This model developed for Karasnagala provides Low values of MRAE and RAEM reflected the very good matching the peakflow magnitude and the shape the opportunity to make better estimates of water recourse . The Synthetic Unit Hydrograph parameters Ct and Cp obtained with systematic calibration and verification process demonstrates the applicability of the method to any ungauged watershed of the region with a short duration of gauged data. The model computations with Concave baseflow separation method revealed an average loss rate of 1.20mm/hr for Karasnagala watershed.
item: Thesis-Abstract
Evaluation of runoff estimation using scs method for infrastructure design - a case study of Attanagalu oya basin- Karasnagala, Sri Lanka
(2015-10-19) Tobgay, S; Wijesekera, NTS
Runoff estimation information on streamflow is a central component for water resource engineering and management. Generally, majority of catchments that demand for water engineering interventions are ungauged. Lack of runoff is a hindrance for optimum infrastructure development. Soil Conservation Service Curve Number method commonly known as the SCS CN method is a popular model elsewhere and in Sri Lanka for runoff estimation in ungauged catchments. One key factor in the use of this model is the determination of Curve Number for the concerned area. Though there are applications SCS model had been carried out for Sri Lanka, the CN estimations had been based on literature recommended values and methods. However the uses of such values require verifications with modeled and observed streamflows. The present study carried out an evaluation of runoff estimation using SCS-CN method developing an event based rainfall runoff model for Attanagalu Oya River Basin at Karasnagala. This study first evaluated the use of literature reported methods for base flow separation and effective rainfall computations to determine the appropriate models for computing direct runoff from the observed streamflows. The SCS CN model developed for the Karasnagala was then tested with a comparison of computed and observed hydrographs. Daily rainfall and runoff data of ten years (1971-1981), 1:50,000 topographic maps, land use and soil data were used for the model development. 60 events were separated after an evaluation of available streamflow and rainfall data. 30 events were used for model calibration and 30 were used for verification. Model evaluation was carried out in several ways. Initially the watershed curve number was determined using standard SCS tables. Then each individual event was calibrated by optimising CN numbers. Average CN from the calibration dataset was then verified using 30 events. Parameter optimisations were done with the Mean Ratio of Absolute Error (MRAE) as the objective function while the Ratio of Absolute Error to Mean (RAEM), ratio of absolute errors corresponding to peak flow, the time to peak and the time base of the hydrographs were computed to reflect the goodness of fit between the observed and modeled streamflows. The present work used the concave method for baseflow separation while the constant loss method was incorporated for the determination of effective rainfall. The weighted catchment average CN for Karasnagala was 85.18. Calibration of the model produced an average MRAE of 0.59. Results of graphical outputs and the errors computed for peak flow magnitude and occurrence revealed that in case of very good model outputs, the MRAE values were well below 0.20. Average optimised catchment CN value during calibration was 70.11. Verification with the average CN value resulted in a MRAE of 0.40 and the outputs demonstrated that the modeled peak flow magnitudes may be considered as reasonable. The entire set of 60 events showed a MRAE of 0.59 for weighted average CN. The average optimised CN for the same set was 70.11 with a MRAE of 0.40. The present work revealed that the estimate of stream flows with CN estimations based on standard tables were of lesser quality when compared with those with the use of average CN value from individual observed event calibrations. It was also identified that the SCS CN model estimations with average optimised CN values for Karasnagala watershed do not produce satisfactorily representative results and hence should be used with caution. While showing a wide disparity in the hydrograph reproduction, the SCS CN model outputs indicated the possibility of using the SCS CN model for computation of peak flow magnitude
item: Thesis-Abstract
Development and verification of a soil erosion model based on OIS to determine erosion hazard zones in a watershed
Chandrasena, KG; Wijesekara, NTS
For Sri Lanka the protection of it's central highland as a watershed is most important because most of development projects in dry areas are based on water and this water is from rivers that now from central highlands. On the other hand in physical terms, soil erosion causes greater damage to agricultural productivity than any other factor. As a result of soil erosion, serious land degradation takes place specially in hilly areas. The occurrence of landslides and flash floods increases the loss of lives and property causing a set back to the country's economic growth. In a limited resources environment this problem of watershed degradation has been neglected for several decades. Therefore, it is of utmost important to address this problem since soil erosion is one of the major problems in watershed management because it directly affects the natural vegetation and also reduces the agricultural productivity. As such in watershed management, it is natural that soil erosion reduction measures are given priority over many other issues. In this context - it is necessary to identify the most vulnerable areas to implement a watershed management programme in relation to soil erosion. The present study is an attempt to contribute towards that goal of selection of vulnerable soil erosion zones. An area was selected in the Gurugoda watershed of Kegalle District carry out a case study. Universal Soil Loss Equation (USLE) was used for computation of soil erosion using a Geographical Information System (GIS) technique. Most parameters appear in the USLE were tested and recommended for Western countries and studies for the tropical countries are limited or non-existent. Parameters for computation using USLE was done through a literature survey. Values of different parameters thus obtained were used to asses. the erosion hazard zones in the study area. The parameters and catchment characteristics such as topography, land cover, soil types etc were incorporated into a layered GIS data base. Overlaying was done to compute the annual soil loss distribution in a spatial context. The zones were classified into three different classes namely the regions with Negligible erosion, Moderate erosion, and Severe erosion A field survey was conducted to identify the actual erosion hazard zones and these zones were also classified in the same manner. Values obtained from field work were compared with the values from USLE and parameters from literature. The comparison of field identified erosion levels with computations, used a trial and error variation of erosion class classification to verify the estimation. The verification of the soil erosion model identified the classification that could be used for watersheds similar to the Gurugoda watershed in the Kegalle District.
item: Thesis-Abstract
Peakflow estimation in ungauged watersheds using flood transposition
Abeynayake, JC; Wijesekera, NTS
Flood estimation is one of the major aspects of hydraulic design and is the first step in planning for flood regulation and protection measures. Proper selection of the design floods is of utmost importance as it effects both the safety and cost of any structure. Too small a design flood for a major structure involves a high risk, not only of total failure of the structure and the service rendered by it but also to the safety of the persons and the property located down stream. An excessive design flood, on the other hand, will result in an unnecessarily costly structure which may adversely effect the economic feasibility of the project. Hence it is required good reliable methods to estimate stream flow at various locations in order to carry out hydraulic design. Flood transposition is a very helpful tool which can be effectively used for design purposes. This allows the transfer of flood information from gauged catchments to other catchments where sufficiently detailed stream flow information is not available. This research deals with a study of annual maximum floods of all four major river basins in the wet zone of Sri Lanka. Peakflows of Kelani Ganga, Kalu Ganga, Gin Ganga and Nilwala Ganga were used for this study. Based on the assumption that peakflows are mostly dependent on watershed area the link between watershed area to its peakflow was studied to find a relationship between watersheds. Seventy-nine watershed combinations in the wet zone of Sri Lanka were analyzed to identify the relationship and the values that could be used for exponent n in flood transposition. Twenty-five watershed combinations out of seventy-nine combinations were within the same basin and the rest is between basins. In order to identify the catchments of which peakflow characteristics are similar, an index called Peakflow Characteristics Similarity Index was defined, When watersheds are similar in peakflow characteristics it was found that the peakflow could be transposed using a function comprising of watershed area only. This relationship showed that peakflow of a particular watershed is proportionate to the nth power of its area and that the n could be taken as 0.8. Average estimated error for this relationship is found to be 34% for catchments within the same river basin whereas an average error of 55% was present for any watershed in the wet zone. Design flow calculations were performed for all similar watersheds using the derived relationship and were compared with those computed with observed values. Design flow estimations using transposed data from the same river basin had an average error of 15%. The error was 40% when the data used for design flow computations was transposed between basins.
item: Thesis-Abstract
Seasonal climate forecasts for water and environmental management
Bulathsinhala, DH; Samarawickrama, S; Subair, L
The network of about 15 meteorological stations in Sri Lanka provides the baseline temperature data upon which most hematological studies are based. Since the data serve many primary users both local and foreign each year, and untold secondary users, quality control is an important consideration/ The quality of the monthly temperature data at the main stations of the Sri lanka Department of Meteorology and Agriculture were evaluated based on station histories, comparison with other stations and internal consistency of the data The Global Historical Climatology Network (GHCN) has previously carried out such quality control for 11 Sri Lankan stations 15 stations, each of which were of a longer duration than used in the GHCN analysis The data that failed to pass the quality control based on multiple checks and consistency of statistical relationships of mean temperature among the different stations were discarded. An estimate has been constructed for the temperature record for each station based on its best-correlated stations alone. The comparison of the actual and constructed data brings out shifts in mean and variance and a technique to adjust the data has been formatted There have been several relocations of stations and changes of instrumentation that caused these shifts Overall, the dataset resulting from this work is more comprehensive while meeting all the standards used in the GHCN work/ The present quality control leads to a much smaller set of data being discarded It is found that major inconsistencies are present in the nineteenth century records of several stations Effective use of available water resources is a serious problem facing the world as it enters the 2P' century An important source of concern in water resources management is the occurrence of severe and sustained droughts that deplete reservoir storage to dangerous levels. Such droughts are often associated with low frequency climatic fluctuations, such as the El Nino Southern Oscillation (ENSO)./ Forecasting future reservoir inflows or rainfall requires an understanding of the nature and causes of climatic variability. There have been significant advances in physically based models of the climatic and hydrologic systems in recent decades. However their operational utility beyond a few days or weeks, and accuracy of their forecasts remain rather limited. /Consequently, where long historical records of the variables of interest are available, statistical approaches could provide a basis for useful seasonal to inter annual flow forecasts Identification of the oceanic or atmospheric variables that fun useful predictors of rainfall is an important step in developing a long-term forecasting model. Third chapter is of a study to develop a framework for rainfall probabilistic forecasting using available climatic information.
item: Thesis-Abstract
Coastal engineering impacts of the proposed Sethusamudran ship channel project
Gunawardena, MJA; Samarawickrama, SP
Abstract Under the Sethusamudram Ship Canal Project (SSCP), the State Government of India will construct a 260 km long shipping canal one section 120 km long from Tuticorin Port to Adam's Bridge, and another 140 km long from Adam's Bridge (North of Rameshwaram) to the Bay of Bengal. Supposedly, it is to be constructed entirely within the territorial waters of India. The canal will have a depth of 12 meters, enabling 10,000 to 12,000 GRT vessels to pass through. During the dredging (estimated to take up to four years), nearly 84 million cubic metres of sand is to be removed from the area. The projected cost of the SSCP is more than USS 1 billion. The whole idea behind the SSCP is ostensibly to save on the travel time which is usually required to skirt around the south side of Sri Lanka in order to get from an eastern seaport in India to the country's west coast. According to the Daily Mirror of July 11 (which quoted a report in "the Hindu" newspaper) the federal government has projected that savings in fuel costs, once the SSCP is completed, will be between USS 1,700 and US$ 4,100 for vessels with loads of 100-500 metric tones. It is estimated by the Indian Government that it will save Indian Rs 2.15 billion (about USS 50 million) in foreign exchange in the first year of its operation in 2008. Though there has been a demand from various quarters for the implementation of the project, there is also opposition to it from environmentalists. They point out that the dredging of the Palk Strait and the Gulf of Manner could affect the ecology of the zone by changing currents, which could: 1. Cause changes in temperature, salinity, turbidity and flow of nutrients 2. Lead to higher tides and to more energetic waves, and hence to coastal erosion. 3. Affect the local sea temperature and thereby alter the pattern of sea-breezes and hence affect rainfall patterns. Hence the main objective of this research study will be: • To find out the changes in hydrodynamic flow regime • To identify changes in sediment transport • To find out possible problems associated with dredged material dispersal and dumping of dredged material • To Identify possible damages to India and Sri Lanka due to future tsunami For this study MIKE 21 HD, ST, PA models have been used. The basic input to the HD model consists of time series data of predicted /water levels in the regional model boundaries, Bathymetry of the area and wind data. In addition to that, field measurement will be required to calibrate the model. But due to lack of filed measurement models are not calibrated to a degree normally expected. Computations were performed on a nested grid set-up starting from a larger regional model and gradually reducing to smaller models while moving towards the area of interest. Objective of this nested approach is to use known tidal constituents to drive the HD model and to arrive at more accurate and finer grid resolutions towards the area of interest./ The boundary conditions for the larger "Regional Model" were based on the tidal constituents from Kalipinya, Tuticorin Port and Cuddlier Port. South The boundary conditions for the larger "Regional Model" were based on the tidal constituents from Kalpitiya, Tuticorin Port and Cuddalore Port. Southern boundary conditions were obtained by interpolating the generated tides of Kalpitiya and Tuticorin Port whereas for the northern boundary, generated tide at Cuddalore Port was directly used. Two small and more refined models were nested within this larger model. The simulations within a sub grid model are based on boundary conditions extracted from the immediately higher model. The nested grid set-up, on which the hydrodynamic modeling was performed The setting up of the hydrodynamic models originated from this "Regional Model" which extends from Kalpitiya/Tuticorin Port in the south, up to Cuddalore Port in the north. The model was set-up with a grid resolution of 1000 m x 1000 m. The size of the model is 200 km x 400 km and The model is oriented with its Y-axis directed 20 degrees westwards./ ern boundary conditions were obtained by interpolating the generated tides of Kalpitiya and Tuticorin Port whereas for the northern boundary, generated tide at Cuddalore Port was directly used. Two small and more refined models were nested within this larger model. The simulations within a sub grid model are based on boundary conditions extracted from the immediately higher model. The nested grid set-up, on which the hydrodynamic modeling was performedThe setting up of the hydrodynamic models originated from this "Regional Model" which extends from Kalpitiya/Tuticorin Port in the south, nnup to Cuddalore Port in the north. The model was set-up with a grid resolution of 1000 m x 1000 m. The size of the model is 200 km x 400 km and The model is oriented with its Y-axis directed 20 degrees westwards.
item: Thesis-Abstract
An Investigation of precipitation patterns in Sri Lanka
Samarasuriya, IDS; Wickramasuriya, SS
Summary. There is increasing scientific evidence that humans arc gradually but certainly changing the earth's climate. The earth's climate is affected by factors that cause a change in the redistribution of energy within the atmosphere or between the atmosphere, land and ocean. Greenhouse gas emissions are altering the atmosphere, creating an uncertain future of global warming, altered patterns of precipitation, and sea level rise for the generations to come./ Therefore, the potential threat of global climate change is a very serious problem collectively faced by humanity as a result of its own activities./ When the hydrological cycle is predisposed by global warming, naturally-occurring droughts will set in quicker, plants will wilt sooner and the droughts will likely become more extensive and longer lasting. The impact of climate change and increase in extreme climate events on water resources will affect human well-being to various degrees, depending on how country-specific water management methods can accommodate such change. Wealthier countries with sophisticated water management systems will be better prepared to deal with the consequences of climate change, whereas poorer nations that are more dependent on seasonal rainfall will be more vulnerable. In general, irrigation may be the first activity to be significantly affected in many countries facing water shortages./ Therefore, a reliable quantification of the potential impacts of climate change on hydrology and water resources is essential for the effective and efficient management of water resources./ Precipitation is the major driving force of the hydrological system. As indicated earlier, a warming trend will intensify the hydrological cycle and significantly affect regional conditions. Changes of precipitation in the amount, intensity, duration and timing during the year will affect river flows and groundwater recharge, but to what degree will depend on the amount of change and the type of catchments. For example, changes in short- duration rainfall characteristics will have a large effect on flood regimes in highly-responsive catchments, but less impact in large, unresponsive catchments, which will be more affected by changes in the rate of occurrence of prolonged wet spells./ The main objective of this research is to investigate & detect any statistically significant trend, periodicity, variability or change in the annual and seasonal precipitation at several meteorological stations in Sri Lanka. A comparison is also made using synthetically generated data, based on the statistical characteristics of the historical data. Despite its tropical nature, the annual rainfall of Sri Lanka exhibits remarkably large spatial and temporal variability. In order to find out the changes, statistical tests had to be applied to analyze historical precipitation records. The method of moving averages is used in the calculations in order to reduce the amount of variation present in the data For simulation, six sets of synthetic time series have been generated for each\ meteorological station using pseudo random numbers.

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