Symposia & Conferences
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Item Spatial variations of macrobenthic assemblage structure along paddy-based runof- river irrigation system: A case study from Colombo, Sri Lanka(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Dasanayaka, D.M.P.I.; Najim, M.M.M.In a paddy-based run-of-river irrigation system, quality of water varies spatially along the river, which influences the biodiversity present in an aquatic ecosystem. With the spatial variations, macrobenthic fauna living along a run-of-river system also vary. The major objective of this study was to analyze the spatial variation of macrobenthos along a run-of-river irrigation system. The selected study area is located in Uduwana near Homagama in Colombo District. The study paddy field is mainly irrigated using two natural streams which are named Kalu Ganga athu ela and Thel Ela and irrigated water is drained to a natural stream named Kunu Ela. Four sampling sites were taken judgmentally as covering different areas of the run-of-river irrigation system. A random sampling technique was employed, and two bottom sediment samples were collected using a Peterson grab sampler on monthly basis from each sampling site between September 2022 to February 2023 (Maha cultivation season). Sediments were wet sieved through 0.5 mm mesh and collected macrobenthos were identified using standard keys. Total abundance, species richness, species evenness, and species heterogeneity were determined separately for the four sites. The spatial variation of total abundance between the four sites was analyzed using one-way ANOVA in MINITAB version 17.0. Similarities of macrobenthos community assemblages were assessed using Bray-Curtis similarity clustering method using PRIMER. A total of 8 macrobenthic taxa (Pila globosa, Lymnaea pinguis, Gyraulus saigonensis, Melanoides turberculata, Hirudo sp., Glyphidrilus sp., Paratelphusa sp., and Chironomidae sp.) were observed from sampling sites. Lymnaea pinguis and Chironomidae sp. dominated in sediment samples and accounted for more than 70% of the total macrobenthic abundance. Sampling site 2 recorded the highest total abundance (N=350) and site 1 recorded the lowest total abundance (N=115) throughout the sampling period. The species richness of the macrobenthic communities was similar in sites 1, 3, and 4 (S=6) while the species richness was 5 in site 2. Since the benthic community was mainly dominated by Lymnaea pinguis, the lowest species heterogeneity (H’) and species evenness (J) values were observed in sampling site 2 (H′ = 0.11; J = 0.79). According to the results of ANOVA, the abundance of Pila globosa, Lymnaea pinguis, and Gyraulus saigonesis showed spatial variations. The cluster analysis separated site 2 from other sites, indicating that the macrobenthic taxa in site 2 are varied compared to the other three sites. Thus, the results revealed that there were spatial variations in the distribution pattern of macrobenthos along a paddy-based run-of-river irrigation system. It is recommended to extend the sampling period to include both Yala and Maha cultivation seasons with more sampling sites to get a better understanding of the spatial variations in the distribution patterns of macrobenthos along the paddy-based run-of-river irrigation system.Item Comparative evaluation of three environmental flow calculation methods at Ketawala anicut of Aththanagalu Oya, Sri Lanka(Department of Zoology and Environmental Management, University of Kelaniya, Kelaniya, Sri Lanka., 2016) Udayanga, N.W.B.A.L.; Najim, M.M.M.Calculation of Environmental Flows (EFs), which are required for the sustenance of aquatic ecosystems in their original pristine state, often emerge as a prominent challenge to the sustainable management of water resources due to their complicity and difficulty of estimation. Being a tropical country that is heavily depended on its agriculture based economy, Sri Lanka often face the challenge of EF estimation during diverse irrigational and drinking water extractions. Lack of technology and expertise, and limitations in the long-term data have directly contributed for the wide utilization of rapid EF estimation methods. Therefore, the current study intends to evaluate the performance of such three widely practiced EF estimation methods, namely Tennant, IUCN and CEA methods for the EF estimation at Ketawala irrigational scheme. The Hydrologic Engineering Centre - Hydrologic Modelling System (HEC-HMS) version 3.5 model was calibrated and validated for the Aththanagalu Oya catchment and the daily river flow values for the past thirty five years (1981-2015) were generated at the pre-weir of the Ketawala anicut. The flow duration curve at the pre-weir of the Ketawala anicut was constructed (via the Gumbel approach) using the above simulated flow regime and the EFs that are applicable for the anicut were estimated via Tennant, IUCN and CEA methods in accordance with the standard methodologies. The Tennant method recommended an EF regime of 4.08 m3/s to be maintained at the post weir of the Ketawala anicut, while IUCN and CEA methods recommended EFs of 11.11 and 11.91 m3/s, respectively. Yet, EFs recommended by all these methods mostly remained higher than the average monthly flows in the dry season while considerably lower than the average monthly flows in the wet season at Ketawala, limiting the practical applicability of the estimated EFs. Furthermore, all these methods remained subjective and less responsive to the variations in the hydrological regime, while neglecting other major ecological components (biota and physic-chemical factors etc.) in an aquatic ecosystem. Hence, regardless of their wide applicably for EF estimation in Sri Lanka, the Tennant, IUCN and CEA methods failed to yield practically and environmentally acceptable EFs for the Ketawala anicut.Item 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.Item Comparison of household sewage disposal systems of a rural and an urban Grama Niladhari Divisions with standards: a case study from North-Western province of Sri Lanka(Department of Zoology and Environmental Management, University of Kelaniya, 2015) Dehipe, D.M.M.C.S.; Chandrasekara, G.B.C.M.R.N.K.; Gnanarathna, U.S.P.; Athettan, S.; Najim, M.M.M.Item Environmental flow requirements for Kinigama anicut in Uruwal Oya, Sri Lanka(Department of Zoology and Environmental Management, University of Kelaniya, 2015) Udayanga, N.W.B.A.L.; Najim, M.M.M.Item Recent trends in the rainfall patterns in the Mannar, Sri Lanka(Department of Zoology and Environmental Management, University of Kelaniya, 2015) Udayanga, N.W.B.A.L.; Najim, M.M.M.Item Evaluation of the spatial and temporal trends of dengue outbreaks in Kolonnawa urban council, Western province, Sri Lanka(Department of Zoology and Environmental Management, University of Kelaniya, 2015) Udayanga, N.W.B.A.L.; Kodithuwakku, K.A.R.K.; Najim, M.M.M.Item Environmental factors influencing living comfort: A case study from Peliyagoda-Gangabada and Gampaha-Keselwathugoda Sri Lanka(Department of Zoology and Environmental Management, University of Kelaniya, 2015) Suriarachchi, R.R.; Sathyajith, J.N.H.; Koralage, R.L.H.; Jayasinghe, A.G.A.D.B.; Kumara, A.S.; Kajani, S.; Najim, M.M.M.Item Effectiveness of domestic solid waste management through provision of composting bins in Rajagiriya, Sri Lanka(Department of Zoology and Environmental Management, University of Kelaniya, 2015) Gallage, V.N.P.; Serasinghe, S.A.N.H.; Brenda, S.J.; Jayathilaka, H.A.P.R.; Anantharaj, C.; Najim, M.M.M.Item Effectiveness of soil conservation measures in tea smallholdings in mid and low country in Sri Lanka(Department of Zoology and Environmental Management, University of Kelaniya, 2015) Gunathilake, G.G.D.; Samanthilaka, G.D.; Erandika, M.K.C.; Nallaperuma, G.L.; Najim, M.M.M.