Master of Science in Water Resources Engineering & Management

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Browsing Master of Science in Water Resources Engineering & Management by Faculty "other"

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    item: Thesis-Abstract
    Applicability of, reference crop evapotranspiration from measured temperature (hargreaves method - 1982) to Sri-Lanka
    Seneviratne, LKP; Kariyawasam, HC
    Considering the problems associated with the availability and reliability of climatic data in developing countries and the possible errors in the more sophisticated methods for estimating crop water requirements, it has become necessary to develop a computational procedure which requires least and widely available data. The method of estimating reference crop evapotranspiration (ETO) from measured temperature introduced. by professor Hargreaves of Utah State University in 1982 has given satisfactory results in many regions of the world. The study of its applicability to Sri- Lanka could do much to improve irrigation and agricultural sectors. Three stations from different climatic regions of Sri-Lanka Here selected with the intention of studying the applicability of this new method. ETG estimates from Modified Penman, Hargreaves and Pan evaporation methods were computed for seven years and the average values Here compared. The results indicated that the Hargreaves method provides, satisfactory’ results for Yala seasons in dry zone. The application of Hargreaves method can be extended even to Maha seasons In dry coastal regions. The ETO estimates from Penman method have given over predictions specially for high wind velocities. Two average years were selected for station Mahailluppallama and Batticaloa. ETO estimates from Modified Penman were computed for varying wind speeds. The results have shown that a local calibration is required for the aerodynamic term of Modified Penman. A relationship has been develop between maximum and minimum temperatures, relative humadities, wind speed and the deviation of ETO values of Hargreaves method from pan evaporation method. This indicated that for given temperatures and relative humidity, Hargreaves method provide better results only for a particular range of wind speed. Estimated crop evapotranspiration (ET crop) for soya beans from Hargreaves and Pan evaporation methods were compared with lysimeter measurements for Agricultural Research Station Mahailluppallama. The total estimated ET crop from Hargreaves method has only varied 5.6 % from the measured lysimeter values.
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    item: Thesis-Abstract
    Investigation of rssouhcs of a limestone aquifer using a digital technique
    De Silva, VW; Senerath, DCH
    Modeling of a limestone aquifer in the north west of Sri Lanka is attempted. The Vanathavillu basin situated 18km north of Puttalum, covering an area of approximately 80sq.km has been studied, using a mathematical model based on an implicit finite difference scheme. The study area situated in the dry zone of Sri Lanka, receives a seasonal rainfall of about 900 mm/year, the most of which falls during the months of October to December. In the Vanathavillu base in there are essentially two water bearing formations: - the miocene sedimentary strata, - the quarternary deposits which overlie the miocene strata. (referred as Moongil Aru formation) Moongil Aru formation consists of a series of clays and silts which partly confines the miocene formation. The piezo-metric levels in the miocene aquifer is lower than the phreatic surface by up to 30 m in the central parts of the region. In the north the piezometric levels are slightly higher than the phreatic surface. The two water bearing formations are interdependent as leakage takes place in and out of the Miocene formation. The model was developed only for the miocene formation and the water table elevation in the Moongil Aru formation assumed constant. The miocene formation is bounded in the east by basement rock outcrops which are relatively impermeable. To the west a fault exists which runs along the coast line. This fault restricts the flow in westerly direction. It is believed that two minor faults exists along two drainage paths of Kala Oya and Moongil Aru. 'The piezometric levels .in the norths suggest that the aquifer discharges into Kala Oya which could be treated as a constant head boundary. In the south the flow directions is entirely towards north. The area has been studied by the Irrigation Dept. and the Water Resources Board of Sri Lanka. On the basis of these investigations aquifer parameters, recharge and abstraction from the limestone aquifer have been estimated. Development plans have been prepared on the basis of these estimates. The purpose of the present model investigation was to access reliability of this estimation and also to provide a tool for planning future development and management of this valuable water resource. A number of model runs with different sets of data representing aquifer parameters, boundaries and flow were made. The results were compared with an available two year record of piezometric levels in the limestone aquifer. Computations were made with one layer model as well as with a simple two layer model. A single layer model with constant inflows or a simple two layer model with water table elevation treated as a constant adequately describe the behavior of the aquifer under the presence level of abstraction. But the behavior of the aquifer with highly increased abstraction can only be model adequately by a two layer model representing both unconfined and semiconfined aquifers together.
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