2017

Permanent URI for this collectionhttp://192.248.9.226/handle/123/13484

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Attempting to improve seasonal performance of Land and water productivity through systematic analysis: Case study of Dahanaka Minor Irrigation Tank in Anuradhapura District of Sri Lanka
Gamage, PR; Wijesekera, NTS
Water conservation in small and medium tanks for agriculture in dry, semi dry and intermediate zones of Sri Lanka are considered as the reason for successful rice cultivation during the period of our ancestors. However, it is often mentioned that the available statistics during last few decades also point to the lower productivity of agriculture under minor irrigation tank systems. The aim is to apply the present guideline recommendations to evaluate a typical dry zone irrigation reservoir system and to make recommendations for farmer livelihood enhancement considering seasonal performance, crop water requirements for paddy and other Food Crops (OFC) and possibilities of suitable crop diversification. System water balance is used to obtain the results in each case and financial analysis used to calculate the income of the farmers. Also it is important to maintain a database for each minor tank because more than 192,000 ha of lands are cultivated under these tanks by contributing considerably to the Sri Lanka economy. Therefore, it is important to find, what are the suitable methods that can be applied to improve the land and water productivity.
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Climate Change Impacts and Adaptation Measures for Pahala Divul Wewa, Anuradhapura, Sri Lanka
Thakuri, PS; Wijesekera, NTS
Present study was carried out to identify possible threats of various climate change scenario and suggest the possible adaptation measures for the food and water security corresponding to irrigation reservoir scale. Pahala Divul Wewa with a catchment area 5.12 km2, in Anuradhapura is located within DL1 agro-ecological zone was selected. The Irrigation Guide-line model was optimized for present situation of irrigable area. Five (5) scenarios of climate change were developed based on literature. Change in the precipitation due Climate change were used for a reservoir operation. The worst climate change scenario for Pahala Divul wewa was identified as the with 22% increase in SouthEast monsoon and 42% decrease in North East monsoon. The cropping intensity under this scenario was reduced from 0.678 to 0.55 a decrease of 13%. Since, Cropping Intensity of Pahala Divul Wewa was noted to reduce, several adaptation measures were identified to minimize the effects. Increasing Canal Efficiency was found to be most effective adaptation measure though it is less economical. It is recommended to incorporate climate change while designing the new schemes and Existing design rainfall, evaporation and other inputs shown in the guidelines need updating.
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Climate Change Impacts and Adaptation Measures in Giritale Reservoir in Polonnaruwa Sri Lanka
Kamran, M; Wijesekera, NTS
Climate change is one of the most important global environmental challenges, which affects the overall system by affecting food production, water supply, health, energy, etc. For study purpose Giritale reservoir in Polonnaruwa district of dry zone in Sri Lanka was selected. Catchment area of the reservoir is 24.3 sq.km and command area is 3075 ha. Data for the reservoir was collected from irrigation department, Colombo and 6 year (2010-2015) rainfall data collected also from irrigation department. This study investigated the impact of climate change, adaption and mitigation measures reservoir system. After a review three scenarios were identified. Scenario 1 rainfall increase 15.8% and temperature increase 8% and scenario2 rainfall increase 14% and temperature increase1.6% and scenario 3 is rainfall is projected to increase by 48% for the Southwest Monsoon by 2050 and Northeast Monsoon, which occurs in the drier northern region, is predicted to decrease by 27–29%. For the worst scenario four adaptation measures were proposed. Among the four only two adaptations could be quantified, and the best adaptation measure was identified. Among scenario option’s, the scenario 2 is the worst scenario and adaptation measure taken for scenario2consist of two options. Option1 is changing the crop type and option 2 is increasing the canal efficiency. For option 1 105 days paddy for Maha and Yala was taken and also green gram for both Maha and Yala was considered and for option2 canal efficiency increased by 10% . Therefore comparing the results adaptation use of green gram improved the cropping intensity by 13%.For verification of result actual rainfall data is not enough and also for predicting the climate trend. Future climate projections indicate that the climate is changing and impacts on agriculture sector can be expected and Worst climate change scenario for the Gritale scheme is when increasing rainfall 14% and also increase the evaporation 6.4%.
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Climate Scenario Identification and Evaluation of Irrigation Responses: Case Study Application of Rambakan Oya Reservoir Using Irrigation Department Guidelines
Deshapriya, WVK; Wijesekera, NTS
Present study was carried out to demonstrate the capability of Irrigation Department Guideline (IDG) model to assess climate change impacts under variety of scenarios by carrying out a case study of Rambakan oya irrigation scheme. The IDG model was optimized for the current irrigable area and verified by checking the irrigable area, spilling months, maximum and minimum storages with qualitative field assessments. Six climate change scenario were developed and three scenarios were identified as critical scenario after evaluating the possible impacts on cultivation extents. Critical scenario were incorporated in to the optimized model in order to evaluate the response and it was observed that a 30% decrease in north-east monsoon (December to February) and 30% increase in south-west monsoon (May to September) keeping the annual total constant would give rise to the highest impact. Annual irrigation demand of Ramabakan Oya reservoir increases by 3% and the cropping intensity reduces from 1.0 to 0.76 and 0.83 to 0.72 in maha and yala seasons respectively. Since cropping intensity of the Rambakan Oya could reduce up to 20% under future climate change scenario, it would be better to incorporate adaptation measures to execute water management plans in the future. Project efficiency enhancement of 7% will allow the present cropping intensity to be maintained under the worst-case scenario for Rambakan oya irrigation scheme
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Computation and Optimization of Snyder’s Synthetic Unit Hydrograph Parameters
Thapa, G; Wijesekera, NTS
In Sri Lanka, the availability of Snyder’s Synthetic Unit Hydrograph (SSUH) parameters are reported only in the Irrigation Department Guidelines and those are limited to only 19 locations. The present study is to determine the SSUH parameters and their applicability to the Karasnagala watershed (52.58 KM2). 60 events corresponding to both North East and South West monsoons during the 1971-1989 period were selected for the model calibration and verification. Considering a balanced representation of both seasons, 30 events were selected for model calibration while the rest were taken for model verification. Events were separated using a minimum inter-event time of 2 days. Effective rainfall corresponding to each event was determined using Phi-Index and incorporating the baseflow separation with the use of Concave method. A one day triangular SUH computed for each event was then converted to curvilinear SUH with the help of SCS dimensionless hydrograph. Mean Ratio of Absolute Error (MRAE) was chosen as the objective function for the evaluation of the total, high, intermediate and low flow estimated by the model. Model verification used the averaged parameter values optimized for each event during model calibration. Averaged calibrated parameters Ct and Cp for Attanagalu Oya Basin at Karasnagala were 3.75 and 0.38 respectively with MRAE value of 0.2. The results obtained were further compared with the recommended ID guideline parameters. The value of Ct and Cp can be applied to the other ungauged areas of the Attanagalu river basin and regions having similar characteristics and consider as the basis for further studies with shorter temporal data resolution.
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Determination of a Design Rainfall Pattern by Comparing with its Effect on Streamflow on Greater Colombo Watershed in Sri Lanka
Keerthirathne, WH; Wijesekera, NTS
IDF curves provide the rainfall quantity corresponding to a particular critical duration and the design return period. In order to carryout infrastructure designs with the use of high resolution mathematical models it is necessary to select the most appropriate temporal distribution of design rain event. In cases of sufficient data availability, literature recommends the use of pattern based location specific design rainfalls for optimum designs. Present study aimed to develop design rainfall patterns based on rainfall observations, and compare with the Alternating Block, Uniform Intensity, and Greater Colombo Flood Design Patterns by evaluating the runoff response from S CS HEC HMS model developed for a sub watershed of Greater Colombo Region. A literature review was conducted to select the design rainfall pattern presently used for water infrastructure engineering.30 years of 15-minute resolution rainfall data of Colombo Meteorological station were used to separate events. Events separation were carried out by nominating Minimum Inter Event Time (MIT) of 6hrs. 220 observed events were separated into six groups considering event durations. Analysis were carried out by developing dimensionless mass curve and percentile curve for each category. Design patterns were developed from percentile curve for each event duration. Design hyetographs were developed for each duration corresponding to design rainfall depth calculated with IDF curves for Colombo and selected data for analysis. Average recurrence Interval (ARI). Runoff response for all patterns were evaluated using the nature of the outflow hydrographs with reference to flood peak and time to peak . It was observed that highest runoff response was given by Enveloped curve developed with observed data. A high runoff variation was observed between rainfall patterns. ABM base pattern can be used with reliable confidence where there is no data for analysis. Criticality Index was developed to account for the pattern of design event with regards to flood peak and time of occurrence. Enveloped curve and 10% probability distribution pattern showed the highest criticality and ABM showed the most consistent criticality for all event categories.
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Drainage Management in an Urban Watershed under Climate Change Scenario using IWRM Concepts
Jayaratne, JPG; Wijesekera, NTS
Surface water and ground water pollution becomes a critical factor in urban areas because having high density of population and infrastructure. Drainage management is very critical and final results is poor water quality status in natural streams when fails to manage the system. This paper aims to demonstrate the capability of developing a water balance model facilitating a quantified watershed management with incorporation of IWRM principles to give solutions for an urban watershed. Then watershed is to be divided in to sub watersheds as necessary in a spatially distributed manner by inspecting the stream network. After that water balance model can be developed considering rainfall, surface runoff, water consumption, return waste discharges of industries and domestic, pan evaporation values and dilution factors etc. Then possible solution can be proposed to achieve a satisfactory water environment for each sub watershed. Subsequently, the situation of growing domestic and industrial units by year 2025 can be evaluated after incorporating a solution for the present situation. In case of climate change, the three scenarios considered a decrease in rainfall of 7%, an increase of 8% in evaporation, a decrease of lowest rainfall and an increase in peak flow. The final output demonstrated the solutions suggested for the worst case scenario.
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Evaluation of Irrigation Water Issue Practice for Better Water Management at Rajangana Reservoir, Sri Lanka
Chemjong, H; Wijesekera, NTS
In most parts of Sri Lanka, water is the critical factor for cultivation. Using the appropriate amount of water is the key factor and therefore efficient water management is very important to increase food production. Common practice of Irrigation water distribution is with the help of Irrigation Department Guidelines. Present work is a study of irrigation water issue practice in Rajangana Irrigation Scheme situated at Anuradhapura which is a district the North Central Province of Sri Lanka. The present study using field data from 2008-2013, computed the theoretical irrigation water requirements as recommended by the Guideline using 75% probable rainfall values and this was named as " Recommended Irrigation Plan", Then this plan was modified with the consideration of actual rainfall that had been experienced during operations. This modification represented the actual water issues that need to be anticipated during operation and hence was named as "Anticipated water use". At the Rajangana Irrigation scheme there is also the actual plan developed for each year along with the water issue at the sluice gate corresponding to the 2008-2013 period. The present research compared the case of Left Bank gravity fed irrigation area which covers an approximate 2500 Ha area with 39 Km tertiary canal network. This area is cultivated mainly with paddy for two main rainy seasons namely "Maha" and "Yala". Water issue model for the study was developed at a weekly time resolution. Comparison of actual water use with the quantities are 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 adjustment 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. Evaluation revealed the need of gauge network, a spatially distributed performance monitoring system and a critical evaluation on the base of present Guideline in order to suitably manage the water utilization in the Rajangana Left bank irrigation scheme.
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Hydrological Modelling Approach for Flood and Water Pollution Control in an Ungauged Catchment - A Case Study in Erewwala Catchment in Bolgoda River Basin, Sri Lanka
Jayasinghe, SN; Rajapakse, LHL
The data scarcity is a widespread, global issue and unavailability of reliable hydro meteorological data is one of the major issues the hydrologists and researchers are facing in Sri Lanka when it comes to water resources planning and management. A significant increase in occurrence of flash flood incidents and water quality degradation in surface water bodies have been noted in the recent past. Hence, developing an approach to identify underlying causes and recommend mitigation or preventive measures for floods and water pollution is a timely requirement that planners, designers and researchers should attempt. The objective of this project is to formulate a hydrological modeling approach to recommend preventive or migratory measures for floods and water pollution in ungauged catchments based on the findings of a case study in Erewwala catchment in Bolgoda River Basin, Sri Lanka. The parameters of hydrological models for ungauged catchments can be estimated using regional information. For this case study, a rainfall-runoff model was developed in spreadsheet and graphical format where the monthly runoff coefficient and base flow were the model calibration parameters. The model was calibrated based on observed data for three years and validated for two years. Observed discharge data at Millakanda gauging station, basin rainfall obtained from Rakwana, Horagoda and Usk Valley rainfall stations and evaporation data from Colombo were used for the model developed for Kaluganga. The calibrated parameters of Kaluganga basin were used for the water resources assessment in Erewwala catchment (2.9 km2). The catchment was divided into three sub-catchments for water pollution control purpose and the incremental runoff at the each sub-catchment outlet node was estimated using the rainfall- runoff model. The types of water uses were identified for each sub-catchment unit and the discharges due to each water use in individual catchments were calculated, subsequently deriving the contribution of each catchment to its overall water pollution. These values were compared with the stipulated permissible pollutant level in surface water bodies. For flood control measures, the HEC-HMS (US-ACE) software was used to estimate the peak discharge with 10 year return period storm event and the peak discharge in each catchment node was obtained. The required flood controlling measures were identified and recommended for the critical catchments which contribute to the highest discharge leading to flashflood conditions in the downstream areas. Based on the peak flow and pollutant source analyses, the sub-catchment No. 1 was identified as the most polluted catchment as well as the one which contributes the most to the flash floods in Erewwala catchment.
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Incorporation of Water Distribution Network Costs in Water Supply System Design Highlighting the Strength of Raster GIS Modelling
Dissanayake, DMSS; Wijesekera, NTS
Design of Water Supply Scheme is very complex and challenging with the numerous options for source, Towers and Network Layout. It demands a several map based analysis to determine suitable layout with intake locations and intermittent storages. Spatial modelling in GIS using a raster format enables a water supply engineer to incorporate the spatial variability, parameter uncertainty, changes to decision objectives, exploring the conceptualizations, and time saving while providing the facility to not only visually explore the result but also to quantify in a meaningful manner. Raster model was developed to demonstrate the strength of GIS and to analyze tower locations and water distribution network layout options in Hanwella DSD area, Sri Lanka. Demonstrating a simple method to incorporate tertiary level pipe networking costs, this case study demonstrates the evaluation of the least cost distribution network for the two alternative tower locations that would produce the same revenue. To demonstrate raster GIS potential in the Water Supply and Drainage sector through a case study application of cost based tower location selection combining the impact of terrain features and consumer settlement distribution. In the present study, three options were considered in order to supply water to the project area with proposed two source points. After obtaining lease cost paths to lay distribution network under each options considered, path costs were compared in order to identify best alternative. There is a 36% Variation of cost between options and Out of three options, third option with the lowest cost will not be an effective option since even though both source points were used, source 1 will be used supply only for two destination points. Both have capability to supply water effectively and economically to particular area. But supplying water with S2 tower will be the best option with 33% less cost compared to highest cost option and only 2% higher than least option.
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Increasing the Cropping Intensity by Changing the Cropping Pattern in a Minor Tank
Alawatugoda, RMMR; Wijesekera, NTS
Water scarcity is the main course for the poor cropping intensities and crop failures in most of the minor tanks located in dry zone. This situation can be addressed in several ways. This study focused on changing the cropping pattern to increase the cropping intensity because this method can be implemented immediately. A minor tank located in Anuradhapura district was selected for the study. Water resources in the catchment was analyzed using the method described in the irrigation department guide line. As the catchment is ungauged 75% probable rainfall of the zone in which the tank belongs was used in analyzing the water availability. Combinations of crop types were considered and paddy and soya bean were selected as the type of crops. Water requirement for both crops were calculated and a water balance study was done for three scenarios. An income comparison between three scenarios were done to find the most beneficial scenario out of the three. As the study was based on the parameters given in the irrigation guideline, present situation was analyzed for the variation of parameters within a range of 25%
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Investigating the Impacts of Climate Change and Adaptation Options in Handegama Tank for Irrigation Water Management
Wangmo, Kinley; Wijesekera, NTS
Under the changing climate, major effects are likely to arise from changes to the freshwater resources systems. The water resources under Hadegama scheme are already stressed and under climate change the availability of irrigation water is expected to become a major issue. This study would help investigate impacts of climate change and adaptation options in Handegama tank for water security. Future scenarios for climate change were selected based on predicted climate information from literature and a reservoir operation was performed under changing irrigation demand. Behavior of the system pertaining to the changes in climatic parameters such as rainfall and evaporation is useful for planning purpose and identifying possible adaptation measures. The worst climate change scenario for Handegama tank was identified as the fifth scenario with decrease in the annual rainfall by 14% and an increase in temperature by 2°C while increasing evaporation by 8 % by 2050. The cropping intensity under this scenario reduced from 1.53 to 1.25, a decrease of 28%. The identified adaptation options were crop diversification and improvement of canal efficiency; both of them increased the cropping intensity by almost 18 %. Reduction in available water under the worst climate change scenario would cause a 28 % reduction in the cropping intensity. These results indicate the need for adaptation under climate change. The adaptation options identified in this study helps to increase the cropping intensity thereby proving to be beneficial to the water users within the system.
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Optimal operating conditions and equilibrium characteristics for rice bran oil extraction
(2013-11-27) Gangodavilage, NC; Amarasinghe, BMWPK
Rice bran is the cuticle between the paddy husk and the rice grain and is obtained as a byproduct in rice processing. The bran contains 15-20 wt% oil and approximately 95% is extractable. Rice bran oil is a very important source of oil, both as an edible oil and non-edible oil. The oil has high medicinal value, due to presence of anti-oxidants, anti-cancer agents, cholesterol reducing agents, skin improving agents, anti-dandruff and anti-itching agents. The oil can also be used for production of soap, surfactants, cosmetic formulations, emulsifiers, textile auxiliaries, synthetic rubber products etc. Experiments were conducted using soxhelt apparatus and the pilot plant scale leaching unit, to extract rice bran oil by solvent extraction, for various brands of rice bran available in Sri Lanka. The key factors controlling the extraction and optimal operating conditions have been identified. Methods of bran pre-treatment, extraction temperature, extraction time, pellet size and FFA content are the factors affecting oil extraction. Analysis of FFA content in the extracted oil shows that steaming is the most effective method of bran pre-treatment. Bran obtained from parboiled paddy has a higher yield of rice bran oil compared to the raw rice bran despite the oil is darker in colour. Comparison of extraction results by various pretreatment methods shows an enhancement of oil extractability due to steaming. Pelletization of bran provides easy percolation and avoids channeling of the solvent and contamination of the oil from fine solids. Equilibrium data shows no preferential adsorption of oil or solvent to the inert bran and approximately constant solid/solvent ratios in the underflow streams. This data can be used in design calculations of solid liquid extraction equipment.
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Possibility of Increasing the Land and Water Productivity of Command Area in Labunoruwa Irrigation Tank, Anuradapura, Sri Lanka
Sharifi, MB; Wijesekera, NTS
In Sri Lanka, farmers prefer to grow paddy because it is their staple food. The most common reason given for the shortfall is the lack of sufficient irrigation water to rescue crop when the rainfall is lean. The lack of irrigation water is dependant of two aspects. One is the lack of storage and the other is the poor water management. Out of the two, the latter is considered very important because it is an activity that can be easily influenced from the first day of recognition. Therefore, the aim of this study is to carry out a systematic case study application demonstrating the potential to investigate the possibility of increasing land and water productivity through the management of crop types (Paddy, green gram, soya bean and cowpea) grown in each season. Irrigation department guidelines were used for computation of irrigation demand, evapotranspiration requirements and selection of the value of crop growth stages, crop factors and land preparation for Maha season and Yala season with 105 days and 135 days duration for paddy and OFC respectively. Land preparation water requirement, farm loss and the project efficiency were assumed as uniform inputs for all spatial units. Reservoir water balance model based on Irrigation Department guideline was applied to determine the smallest capacity of reservoir that would be required for cultivation of the largest required irrigable area for a pre-determined cropping pattern and intensity for both seasons. After computation of irrigation demand and reservoir water balance modeling, it was found that in all four options, full command area (100%) could be cultivated while in Yala season this result differs as follows. In option 1, paddy was considered for 16% of the command area, while in option 2 this cultivation could be as 10 % of the command area paddy and 28% of the command area green gram. In option 3 and option 4, the cultivable areas were found as 10% for paddy along with 19% for soya beans and 10% for paddy along with 21% for cowpea respectively. Consequently, the second option in which 10 % of the command area was considered for paddy and 28% of the command area for Green Gram was found as a best option to be practiced under Labunoruwa Irrigation Tank in order to increase the water productivity.
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Potential of Water Balance Modelling with Surface Water Pollution Considerations to Manage Ungauged Watersheds with an Emphasis on Multi User Concepts – Demonstrating an Application at a Watershed in Dampe, Sri Lanka
Dahanayake, AC; Wijesekera, NTS
Practicing integrated water resources management (IWRM) for sustainability is vital when there is multi user competition for the finite fresh water resources. In order to facilitate early decision making, it is necessary to evaluate ungauged small watersheds with simple, easy to apply but quantitative tools. This paper demonstrates the possibility of successfully applying the multiuser concept, the finite nature of water and system water balance, as a mean to overcome the surface water pollution in Dampe watershed (0.62km2), Sri Lanka. Since this watershed is ungauged, field visits, gauged data from the locality, estimates from available literature were used for a rational application of water balance to evaluate solutions for surface water pollution. The watershed runoff was calculated using a two parameter water balance model which enabled soil moisture accounting. The monthly water balance model for Dampe watershed which included multi sectoral water uses, the surface water quantity and quality at each key stream node for each sub catchment enabled the analysis of several scenarios. Remedial measures to overcome the problem and sustainable methods to preserve water for the future generation are proposed.
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A Quantitative Analysis of Surface water in the Uruboku Oya basin Demonstrating the Application Potential of IWRM Principles to Complex Irrigation Systems
Jayadeera, PM; Wijesekera, NTS
Utilizing IWRM principals to manage water resources is often limited to policy and institutional options which are qualitative in nature (Mehta et al., 2016). Though application friendly modelling examples which satisfactorily incorporate both water quantity and thresholds of quality are essential for watershed managers to ensure educated participatory management the lack of detailed case studies has been noted as a gap that needs to be filled. Muruthawela irrigation scheme of Uruboku Oya basin in Hambantota district of Sri Lanka having a medium scale reservoir of 47.8 MCM capacity, a source area of 4400 ha, and a command area of 1710 ha was taken as a case study. Irrigation, water supply & sanitation, hydro power, inland fishery and environment are the competing water use sectors associated with the system. This system which frequently experiences water conflict situations has limited data to evaluate sectoral water uses. A water balance model for this system was developed to assess multiple water uses by incorporating both water quantity and quality. A situation analysis was carried out with available measurements, guidelines and rational approximations using field observations. This study with an order of magnitude water balance study demonstrated the capability to evaluate the present water conflict scenario and then propose a solution to manage the water quantity and water quality of the system to satisfy all stakeholders. The study concluded that the alternative of IWRM can increase the cropping intensity of Muruthewela scheme by 35% (up to 100%) in maha with introduction of cowpea and allocation of 55.6 MCM for total Irrigation demand while allocating 0.9 MCM annually for water supply and sanitation sector. Pollution status in downstream of Muruthewela tank were evaluated at three locations, Node A –Udukiriwila, Node B-Wakamulla & Node C-Andupelena in order to identify the most vulnerable section for pollution due to agricultural & domestic return flows. The threshold value of dilution was taken as 8 as recommended by Central Environmental Authority (Central Environmental Authority, 1980). The study found that Node C-Andepelena is the most vulnerable section for pollution and the priority area which needs attention by all stakeholders. Pollution level at Node B-Wakamulla can be managed to a certain extent by releasing an environmental flow of 2.4 MCM (4.3% of Irrigation demand) annually
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A Raster GIS Model for Water Supply Tower and Source Option Prioritisation in Community Based Water Supply Schemes at Attanagalla, Sri Lanka
Kumari, TKNK; Wijesekera, NTS
Optimum location identification for the water tower and source is very important for any water supply scheme mainly due to storage capacity, elevation, landuse, yield of the source throughout the year, and the costs for transmission and distribution system. Towers need water from several alternative sources. Construction of distribution pipe lines is expensive due to physical features, terrain, water and urbanisation. Considering these factors design option prioritisation can be carried out by using Raster GIS. To demonstrate the potential of Raster GIS a case study was undertaken for the prioritisation of source locations for a Community Based Water Supply Scheme (CBWSS) to deliver safe and reliable drinking water for rural community living in approximately 64 km2 within Attanagalla of Gampaha District. A Raster GIS model was developed to prioritise the community based water supply scheme by using terrain features with the resolution of 10 m. Base layers for the key parameters of population, roads, elevation, land use, soil, rainfall and streams were prepared and analysed to obtain the final output. Four options of two tower and two source locations for CBWSS were evaluated and Ihalagama & Algama were selected for water tower & source respectively. This paper demonstrates the weighted overlay for the cost surface (60% Road +30% Slope+10% Soil) and the least cost path for transmission and distribution (5,486,173.50 in Cost units) and close proximity to the urban area was selected. Raster GIS can overlay the layers easily, has terrain modelling capability and incorporates cost functions. Therefore Raster GIS is a great facilitator for spatial modelling for the prioritisation of planning and management of water supply schemes.
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Raster GIS Modelling when Selecting a Suitable Solid Waste Dumping Site
Rathnayaka, RMLU; Wijesekera, NTS
Disposal of solid waste is a major problem which is rapidly increasing with the growth of population and development of industries. In a majority of places, open pits have become major disposal locations causing severe environmental and health issues. Since, solid waste disposing is an important part of a waste management system, locating proper sites for solid waste disposal is considering main issue for the management of solid waste. Site selection involves working with several map layers while requiring qualitative assessment for decision making. Multiple layer operations can be carried out by using Geographic Information system and is a suitable method for site selection. Vector and raster data models are the primary data models used in GIS. The present study is intended to demonstrate the capabilities of raster GIS formats in suitability analysis by finding out a suitable site for the disposal of urban solid waste generated from Rathnapura municipality. Concept and the objective function were identified and the factors which are necessary to achieve the aims of study were determined by reviewing literature. AHP technique in combination with GIS overlaying was used to arrive at optimum weights for each parameter. In literature land use, water bodies, flood risk zones, streams, population density, protected area, major roads, landslide prone zones, water supply sources, ground water depth, proximity to roads, rainfall, build-up areas, slope and soil are described as factors affecting land selection. According to the results obtained, 0.59 km2 of area was suitable for solid dumping site. In Raster GIS multilayer operations can be perform and overlaying process is very fast, causing data analysis is quick and easy. GIS technique is a better tool for suitability analysis as it reduce time and cost of site selection..
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Study of Urban Water Demand and Distribution System Reliability – A Case Study of Maharagama Water Supply Scheme, Sri Lanka
Dissanayake, DMSS; Rajapakse, RLHL
Significant variation of flow could be identified during the day for Maharagama water supply scheme. Diurnal problem curve indicates that there is a significant problem level, which is more than 40% of service level, during the day. The system operates at a low Hourly Peak Factor (HPF) value of 1.5, moderate Minimum Night Flow Factor (MNF) of 0.4 and Daily Peak Factor (DPF) of 1.1. Water supply system pumping capacity was found to be inadequate to cater the peak demand of the scheme. It reveals that elevation and the distance have a considerable effect on Level of service for Maharagama WSS and Service level has a significant effect on consumption quantity as well, affecting overall revenue. Aim of this study is to assess water demand, evaluate distribution performance of semi urban water supply scheme, and propose management recommendations as an initial approach that will eventually lead to the development of established guidelines for system assessment and operation. In the present study, monthly consumption per connection derived for the past 13 years from 2002 to 2014 and the daily average flow obtained for Mondays through Sunday for five weeks were studied by applying multiple statistical analysis using Small Samples Theory (SMT). A System Water Balance Model was used to generate the instant flow rate time series of demand from the available service reservoir level data and pumping data. Generated out-flow time series was analyzed using Large Sample Theory of statistics. Level of service variation with the proposed parameters was assessed with Principle Component Analysis (PCA) and simple tabular methods. Results were verified with field surveys con-ducted across the study area. The purpose of a water supply distribution system is to provide safe drinking water to each consumer with adequate quantity and acceptable quality. For the operational as well as designing aspects, it is crucial to estimate water demand that is how much water is needed and the variation in demand that is when it is needed. Every year, more than 100,000 new consumers are added to the National Water Supply and Drainage Board (NWSDB) database and the demand for pipe borne water is ever increasing. Out of the piped schemes maintained by NWSDB, only 36% has the capacity to provide 24 hour supply (NWSDB, 1998). Hence, the demand is a very important parameter which requires due consideration when considering urban water supplies.
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Sustainable Solutions for the Drying Up of Groundwater Wells – A Case Study in a Selected Watershed in Dampe, Sri Lanka
Dahanayake, AC; Rajapakse, RLHL
Groundwater has now become a limited resource due to the adverse impacts of various natural and anthropogenic causes. Due to the increasing population and rapid urbanization, the demand for groundwater has been ever in-creasing. Consequently, the occurrence of declining groundwater tables and drying up of wells have been reported in different parts of the country. In order to identify adverse impacts and facilitate early decision making, it is necessary to assess and evaluate ungauged small watersheds with simple, easy to apply but quantitative tools. This paper demonstrates the possibility of successfully applying a conceptual, lumped parameter rainfall-runoff model based on water balance approach (The ABCD model) in combination with a basic (Single Basin) HEC-HMS model to identify a comprehensive solution for the drying up of groundwater wells, for Dampe watershed (0.62km2), Sri Lanka. The model was used to carry out a quantitative analysis of groundwater storage and identify the interaction with land use pattern, and it was developed by using gathered and simulated usage and recharge data of the surface and groundwater basins. Several scenarios have been analysed using the ABCD model, in order to identify the ground-water depletion at the present condition, in the future condition (with 50% increase in the impervious area of the catchment) and the proposed solution scenario, which is to increase the pervious area of the catchment. The developed single basin HEC-HMS model has been used in order to determine the peak flow associated with a 10-year re-turn period storm event. Remedial measures to overcome the problem and sustainable methods to preserve water for the future generation are proposed based on the findings of the study.

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