Browsing by Author "Halwatura, D."

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Application of the HEC-HMS model for runoff simulation in a tropical catchment
(Environmental Modelling & Software, 2013) Halwatura, D.; Najim, M.M.M.
Diversity of ichthyofauna in an abandoned and an active paddy field in Boralugoda GN Division in Kaduwela municipal council area
(Sri Lanka Association for Fisheries and Aquatic Resources, 2012) Halwatura, D.; Wattavidanage, J.
Paddy fields are manmade wetlands which provide habitats for a large number of freshwater fish species. Owing to uncontrolled reclamation and usage of pesticides. most of freshwater fishes are wiped out them. Therefore. this study attempted to determine the diversity of the ichthyofauna in an active and an abandoned paddy field. The studied paddy fields are located in Boralugoda GN division (489/A) in Kaduwela municipal council area. The paddy fields are located within the catchment area of Kelani River. During the study fish species at six selected sites. three from active area and three from abandoned area were collected from the hand net by using random sampling method and their species diversity and species richness were determined. Physico-chemical parameters in water such as pH. temperature. visibility and flow rate were also measured. In addition. anthropogenic activities and the distribution of peripheral and submerged vegetation were recorded. Data were collected once a week from January to June 2009. According to the results. a total of 19 species were detected from the abandoned paddy field sites while 16 species were detected from the active sites. In abandoned and active paddy fields. 6 and 4 endemics were found respectively. The mean abundance of the species in cultivating sites were significantly lower than the abandoned sites (P
Environmental Flow Assessment in Attanagalu Oya
(Sri Lanka Association for Fisheries and Aquatic Resources, 2012) Halwatura, D.; Najim, M.M.M.
Protecting and restoring river flow regimes and hence the ecosystems that they support by providing environmental flows has become a major aspect of water resource management in river basins. It is difficult to quantify the amount of flows that could be removed from a river while maintaining desired ecosystem conditions. This study focused on to determine the optimum flow that has to be maintained along the Attanagalu Oya and sufficiency of water to sustain riverine ecosystem and other requirements with future water demands. Water withdrawal data for drinking and irrigation were collected from the Water Supply and Drainage Board and Department of Irrigation, respectively. Daily flows were generated for past 50 years and for next 30 years by calibrating and validating the HEC-HMS 3.4 model for the Attanagalu Oya catchment. Simulated stream flows were characterized using 36 different hydrological parameters separately for the past 50 years and for the next 30 years. The Range of Variability Approach (RVA) targets and rate of non-attainment of the flows for the past and the future scenarios were calculated using original flows before water withdrawals. According to the RVA approach, environmental flow has not being maintained at present in the Attanagalu Oya. Mean rate of non-attainment of the indicators of Hydrologic Alteration (IHA) groups after water withdrawals vary in between 12% to 80%. If the rainfall pattern of the next thirty years shows the maximum rainfall of past fifty years, the mean rate of non-attainment would be 45%. Hence, any development project that deal with water withdrawal or any damming across the Oya needs broad analysis of environmental impacts due to changes in flow regimes that could have an adverse impact on the ecosystem and associated functions along the river.
Environmental Flow Assessment–An Analysis
(Journal of Environmental Professionals Sri Lanka,, 2014) Halwatura, D.; Najim, M.M.M
Natural flow of a river is recognized as vital to sustaining riverine ecosystems. The biotic composition, structure and function of aquatic ecosystems depend largely on the hydrologic regimes; however flows of the world’s rivers are increasingly being modified through impoundments. Therefore calculation of the optimum flows for a healthier river is essential but there is no simple figure that can be given for the environmental flow requirements of rivers. Environmental flows refer to water for ecosystems. Ecosystems, however, provide a wide range of valuable services to people. Concept of the environmental flow was initiated not only to discover the river health and to manipulate river flow regimes, but also to get the maximum harvest from free flowing waters. Hence, providing for environmental flows is not exclusively a matter of sustaining ecosystems but also a matter of supporting human well being. As demand for freshwater continues to rise and ways are sought to improve water productivity, decision-making bodies at local, basin and national levels require accurate information on the role of river flows in sustaining a wide range of environmental benefits. For that reason assessment of environmental flows may contribute to setting management rules and monitoring their impact on river health.
Impacts of Urban Water Management in Attanagalu Oya Basin
(Conference on Structural Engineering and Construction Management, 2013) Halwatura, D.; Najim, M.M.M.; Udayanga, N.W.B.A.L.
The demand for water in most parts of Sri Lanka has intensified within the recent years due to the increase in population growth and urbanization. Thus, the quantitative allocation of the available water resources to support the elevating demand for water by numerous sectors while maintaining harmony with the nature has been a challenge for the local and national authorities. Quantification of amounts of river flows that should be extracted to support the increasing demands for water with less or no impacts on the riverine ecosystems is difficult. Therefore, this research focuses on studying the impacts of urbanization on the demand of water by various sectors and employing advanced hydrological models to quantify the extractable amount of river flow while maintaining optimum flows along the Attanagalu Oya that have to be maintained to sustain the environment via assessment of environmental flow assessment to predict whether the flows of Attanagalu Oya would be sufficient enough to support riverine ecosystems and other requirements. HEC-HMS model was calibrated and validated for the Attanagalu Oya catchment and daily flows were generated for the period of 1960-2010. The past and future demand for water up to 2030 was quantified considering the extractions for urban water supply and irrigation and the simulated stream flows for the past fifty years and the future years were characterized using thirty two different hydrological parameters. The Range of Variability Approach (RVA) targets that should be maintained within the Attanagalu Oya were calculated using original flows before water extractions and diversions along with the rate of non-attainment of the flows for the past and the future scenarios. When the period of 1960-2010 is considered the mean rate of non-attainment of the Indicators of Hydrologic Alteration (IHA) groups after water withdrawals vary in between 12% to 80%. But when the future years (2010-2030) are considered a mean rate of non-attainment of 51.4% (if the rainfall patterns remains unchanged) or 79.0% (if the rainfall pattern is reduced to the worse as the minimum rainfall received in the past fifty years) or 48.6% (if the rainfall pattern of the future years exhibit a maximum rainfall of past fifty years) could be predicted for Attanagalu Oya in accordance to the RVA approach which are higher compared to the past. This situation will aggravate with the increase in urban water demand.
Influence of climate change on water management of Paddy in Attanagalu Oya basin
(Symposium proceedings of the Water Professional?s Day, 2013) Waniganethti, D.; Najim, M.M.M.; Halwatura, D.
Runoff Modeling of a Wet Zone Watershed in Sri Lanka Using HEC-HMS Model
(Sri Lanka Association for Fisheries and Aquatic Resources, 2012) Halwatura, D.; Najim, M.M.M.
Flows of the world's rivers are increasingly being modified through impoundments to conserve and develop water resources and therefore estimation of river flow and their variations are vital. Information on rainfall and resulted stream flow patterns are essential for sustainable exploitation of river resources, but stream flows are not available at locations of interest. HEC-HMS is a reliable model developed by the US Army Corps of Engineers that could be used for hydrological simulations, but this model is not calibrated and validated for Sri Lankan watersheds. This study employed three different approaches to calibrate and validate the HEC-HMS 3.4 model to Attanagalu Oya catchment and generate long term flow data for the river and its tributaries. Daily rainfall data from five rain gauging stations (Vincit, Chesterford, Kirindiwela, Nittambuwa Pasyala and Henarathgoda) for past 20 years scattered in upper and middle Attanagalu Oya catchment, SO year daily rainfall data and 20 year monthly evaporation data for agro meteorological station Henarathgoda in the lower catchment jointly with daily flow data at Dunamale from 2005 to 2010 were used in the study. GIS layers that were needed as input data for the model were prepared using Arc GIS 9.2 software. Three methods were selected for the model calibration process, soil conservation service (SCS) curve number loss method, deficit constant loss method (Snyder unit hydrograph method and Clark unit hydrograph method). Calibration was carried out for Dunamale sub catchment using daily flow data from 2005-2007. Validation was achieved with a new set of daily rainfall and flow data (2008 - 2010). As the loss method, the SCS curve number method did not perform well even though it is used widely for flow simulation in Sri Lanka. Instead of SCS curve number method, deficit constant method was employed with reasonable accuracy. According to the results Snyder unit hydrograph method could be recommended as the best transformation method for the Attanagalu Oya basin compared to Clark unit hydrograph method. It is concluded that combination of these two methods can reliably be applied in order to simulate river flows in the country since there are ample of un-gauged rivers located in the wet zone of Sri Lanka.
Seasonal Variation of Rainfall at Attanagalu Oya Basin
(symposium proceedings of the Water Professional?s Day, 2012) Waniganethti, D.; Najim, M.M.M.; Halwatura, D.