Master of Engineering in Water Resources Engineering & Managementhttp://dl.lib.uom.lk/handle/123/161252024-03-29T11:24:43Z2024-03-29T11:24:43ZIdentification of water management concerns in irrigation - study of water issue practice at rajangana reservoir, sri lankaChemjong, Hhttp://dl.lib.uom.lk/handle/123/134012023-10-13T02:25:13ZIdentification of water management concerns in irrigation - study of water issue practice at rajangana reservoir, sri lanka
Chemjong, H
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.
Development of a rainfall runoff model for Kalu ganga basin of Sri Lanka using HEC-HMS modelJayadeera, PMhttp://dl.lib.uom.lk/handle/123/128002022-10-12T03:29:22ZDevelopment of a rainfall runoff model for Kalu ganga basin of Sri Lanka using HEC-HMS model
Jayadeera, PM
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.
UntitledJaman, Mhttp://dl.lib.uom.lk/handle/123/114772022-10-12T03:11:48Z2015-10-19T00:00:00ZJaman, M
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.
2015-10-19T00:00:00ZEvent 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 LankaThapa, Ghttp://dl.lib.uom.lk/handle/123/114762023-10-13T00:12:09Z2015-10-19T00:00:00ZEvent 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
Thapa, G
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.
2015-10-19T00:00:00Z