International Symposium on ICT for Environmental Sustainability (ICTES 2014)
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Item Environmental Flow Variation due to Mini-Hydro Diversion at Gurugoda Oya, Sri Lanka(Department of Zoology, University of Kelaniya, Kelaniya, Sri Lanka, 2014-06) Munasinghe, D.S.N.; Najim, M.M.M.Quantification of amounts of flows that could be diverted maintaining desired ecosystem conditions is difficult, and thus, water allocation among sectors including the environment, has emerged a growing concern in Sri Lanka. Therefore, this research focused on quantifying optimum flows that has to be maintained below the weir site of a mini-hydro power plant located at Morontota, Sri Lanka through Environmental Flow Assessment and to predict whether the flows of the Hungampola South/Morontota village section of Gurugoda Oya would be sufficient to sustain riverine biodiversity. The HEC-HMS 3.5 model was calibrated and validated for the Holombuwa catchment of the Gurugoda Oya basin. The GIS layers that were needed as input data for flow simulation were prepared using Arc GIS 10.0 and the calibrated and validated model was applied to the Alapalawela sub catchment located within the Holombuwa catchment, to generate flows for the past twenty three years (1991-2013). Simulated stream flows were characterized using thirty two different hydrological parameters. The Range of Variability Approach (RVA) targets to be maintained below the weir site were calculated using flows before hydropower diversions, and the rate of non-attainment of flows were determined for past scenarios (2011-2013). According to the RVA, Environmental Flow is not maintained at present in Gurugoda Oya below the weir. Mean rate of non-attainment of the flow of Gurugoda Oya after mini hydropower diversion is around 45% suggesting moderate level of hydrologic alteration due to impoundment. Rate of non-attainment of the indicators of hydrological alterations (IHA) group 1 parameters are in between 33% - 100%. Except for the magnitude and duration of rate of non-attainment of means of 90 day minima and all maxima values which attain a steady 0%, all other group 2 parameters vary between 33% - 67%. In the IHA group 3, timing of lower limit of annual extreme water condition could not be calculated because flow of Gurugoda Oya assumes the same minimal flow for several days, showing more than one annual minima. Annual maxima show a rate of nonattainment of 33%. Rate of non-attainment of the IHA group 4 and 5 both vary between 0% - 100%. Therefore, Hydropower diversions from Gurugoda Oya that deals with damming of the stream needs extensive analysis of environmental impacts due to changes in flow regimes. The RVA targets defined by this study could be of significance for ecosystem management and restorations plans, and could provide ecological operations for the weir.Item Flow Modelling in Nillambe Oya, Sri Lanka(Department of Zoology, University of Kelaniya, Kelaniya, Sri Lanka, 2014-06) Gunawardena, M.P.; Najim, M.M.M.Flooding and flow changes in rivers and streams due to anthropogenic activities are the major problems worldwide as well as in Sri Lanka. To address these issues, proper monitoring of flow patterns and prediction of flow changes are necessary; However, daily monitoring and data collection is greatly time consuming and costly. Therefore, development and application of models for accurate simulation of flow variations will be a vital requirement for the management of these ecosystems. In order to address these concerns, a study was done with the objective of calibrating and validating a model based on climatic, landuse and flow data and to determine whether the calibrated model could be applied to predict flow variations. HEC-HMS 3.5 model which was developed by the United States Army Corps of Engineers was used to simulate flow variation of the Nillambe Oya catchment which is located within the central highlands of the mid and upcountry wet zone. During the period from May 2013 to September 2013, flow was measured in nine selected days. Rainfall data, other meteorological data and flow data for eight years (October 1991 to September 1999) were obtained from the Environment and Forest Division of the Mahaweli Authority and the Meteorology Department of Sri Lanka. Daily flow data for five years (October 1991 to September 1996) were used to calibrate the model and another set of flow data for five years (October 1994 to September 1999) were used to validate the model. The flow values that were measured in situ during May 2013 to September 2013 were statistically tested with flow values simulated by the model. Obtained residual plots and calculated percentage residuals of the calibration and validation produced results with high R squared values (above 0.65) and residual percentages within ±1SD and ±2SD above 85% and 95%, respectively. The properly calibrated and validated HEC-HMS 3.5 computer model can be reliably used to simulate flows of Nillambe Oya. Snyder unit hydrograph method, as the transformation method, simulates flows reliably in the study catchment, along with initial loss method. Therefore, HEC-HMS 3.5 model can reliably be used to estimate flow volumes that are available to Hydropower generation, drinking water supply and agricultural purposes while maintaining ecological harmony with the riverine ecosystem.Item Evaluation of the trends in climate change with respect to severity and frequency of occurrence of wet and dry events of rainfall in Aththanagalu oya basin(Department of Zoology, University of Kelaniya, Kelaniya, Sri Lanka, 2014-06) Udayanga, N.W.B.A.L.; Najim, M.M.M.Socioeconomic aspects of life have changed due to alterations in the climatic patterns. Sri Lanka needs to pay more attention to the climate extremes as the available water resources are directly affected by these changes. Hence planning and management of water resources based on climatic patterns play a key role in sustainable development. Sustainable planning and management of water resources of Aththanagalu Oya that feeds many large and small scale multi-purpose water extraction schemes in Sri Lanka is vital in the event of climate change. Thus, an analysis of the shifts and trends of climatic patterns with respect to wet and dry events within the Aththanagalu Oya basin was carried out to evaluate the state and the extent of climate change using Standardized Precipitation Index(SPI). Daily rainfall data covering the period from January 1991 to February 2011 of Henarathgoda, Vincit, Chesterford, Kirindiwela, Nittambuwa and Pasyala rainfall gauging stations which are located within the Aththanagalu Oya catchment area were obtained from the Department of Meteorology, Sri Lanka. Two periodic intervals of years (1991-2000 and 2001-2011) were formulated and monthly accumulated rainfall for each month of the considered periods were used as the input to the SPI Model in Mat Lab R2007b (version 7.5). The events were ranked into five classes (normal, mild moderate, severe and extreme) based on the severity of each event and the variations in climate (with respect to SPI) were evaluated using Paired Chi-Square method. A decrease in dry events and an increase of the wet events in the climatic pattern of recent years (2001-2011) compared to the past (from 1991 to 2000) in Vincit, Kirindiwela, Nittambuwa and Pasyala could be observed in accordance with the SPI analysis while an opposite trend was observed in Henarathgoda and Chesterford. Unlike the predictions of many studies which expect significant alterations in climate patterns in the recent years than the past years, according to the SPI approach, only the wet events of Pasyala (a significant increasing trend of wetness) and the dry events of Vincit (a significant decreasing trend of dryness) indicate significant alterations in climatic patterns while the climatic variations indicated by the rest of the areas are statistically insignificant. Hence, a significant increase in wetness in Vincit and Pasyalain terms of both severity and frequency of occurrence with variations of rainfall seasonality could be predicted in accordance with the SPI.