Browsing by Author "Gunawardena, M.P."

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Adapting Sri Lanka to Climate Change: Approaches to Water Modelling in the Upper Mahaweli Catchment Area
(Climate Change Research at Universities. Springer, Cham, 2017) Gunawardena, M.P.; Najim, M.M.M.
Water flow and water quality changes in surface water bodies due to climate change is a major problem worldwide, typically in river eco-systems. To address these issues, proper monitoring of river flow variations and water quality is necessary, but daily monitoring and data collection is greatly time consuming and costly. Therefore, a study was done with the objectives to calibrate and validate the HEC-HMS 3.5 and HEC-RAS 4.1.0 models to simulate flow variation and water quality variations respectively in Nillambe Oya, Sri Lanka. The development of such models are a significant requirement in the present scientific world to predict river flow and water quality variations as an adaptation for the climate change. The HEC-HMS 3.5 model was used to generate flow which is needed for HEC-RAS 4.1.0. Daily flow data for five years (from October 1991 to September 1996) were used to calibrate the HEC-HMS 3.5 model and another set of daily flow data for five years (from October 1994 to September 1999) were used to validate the model. HEC-RAS 4.1.0 model was calibrated using water quality data collected and analyzed in five days. The validity of the calibrated model was evaluated using water quality data collected in the other four days. The calibrated and validated HEC-HMS 3.5 model reliably predicted the flow in Nillambe Oya. The calibrated and validated HEC-RAS 4.1.0 model simulated Dissolved Oxygen (DO), Biological Oxygen Demand (BOD) and Nitrate Nitrogen (NO3-N) splendidly. Orthophosphates was also predicted reliably by the model, but the simulation of organic Phosphorus was not that sensible.
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.
Sediment modelling in Nillambe Oya, Sri Lanka
(Department of Zoology and Environmental Management, University of Kelaniya, Kelaniya, Sri Lanka., 2016) Gunawardena, M.P.; Najim, M.M.M.
Sedimentation in surface water bodies is a major problem worldwide as well as in Sri Lanka especially in the upper Mahaweli catchment. To address these issues, proper monitoring of sedimentation is necessary, but daily monitoring and data collection are greatly time consuming and costly. Therefore, development and application of models for accurate simulation of these variations will be a vital requirement for management of these ecosystems. Therefore, the present study was done with the objectives of calibrating and validating the HEC-HMS 3.5 and HEC-RAS 4.1.0 models based on climatic, sediment and landuse data and applying the calibrated models to predict sediment variations. With the purpose of addressing this issue, combination of HEC-HMS 3.5 and HEC-RAS 4.1.0 models were used to simulate flow and sediment changes in the Nillambe Oya, which is located in the upper Mahaweli catchment with typical landuse patterns of the central highlands of the mid and up country wet zone of Sri Lanka. During the period from May 2013 to September 2013; flow was measured and water samples were analysed for sediment in nine selected days. Rainfall data, other meteorological data, flow and sediment data were obtained from the Environment and Forest Division of the Mahaweli Authority and the Meteorology Department of Sri Lanka. HEC-HMS 3.5 and HEC-RAS 4.1.0 models which are developed by the United States Army Corps of Engineers were used to simulate flow and sediment of the Nillambe Oya. The HEC-HMS 3.5 model was used to generate flow which is needed for HEC-RAS 4.1.0 model in order to perform simulation of sediment in Nillambe Oya. Daily flow data for five years (from October 1991 to September 1996) were used to calibrate the HEC-HMS 3.5 model and another set of flow data for five years (from October 1994 to September 1999) were used to validate the model. HEC-RAS 4.1.0 model was calibrated using sediment data collected and analysed in five days along with flow and other meteorological data. The validity of the calibrated model was evaluated using sediment data collected in the other four days. The calibrated and validated HEC-HMS 3.5 model reliably predicted the flow in Nillambe Oya. The HEC-RAS 4.1.0 model simulates only the sediment derived from river scouring and it cannot simulate the sediment resulting from watershed erosion. According to the model simulations, the sediment concentration derived from river scouring varies from 6.9% to 10.3% when compared to the total sediment load. On average, 92% of the sediments carried by the river is resulted from watershed soil erosion. Therefore, proper watershed management actions should be taken in order to reduce the sediment load carried by the Nillambe Oya and also to minimise the impact of sedimentation of the Nillambe reservoir.