Kelani River Basin Research Articles

Event Based Flood Inundation Mapping Under the Impact of Climate Change: A Case Study in Lower Kelani River Basin, Sri Lanka

The downstream low lying region of the Kelani River including the Colombo suburbs, experience severe inundation due to localized heavy rainfall events and high precipitation in the upper basin. Under the impact of climate change it is very likely that more frequent heavy rainfalls in tropics [1] will occur. Therefore it is extremely important to have a better understanding about future rainfall patterns and intensities in the basin and inundation extents of the low lying regions characterized by high population concentration and economic activities that form the suburbs of the commercial capital. This paper presents the extreme rainfalls occurrence potential and resulting flood inundation along the lower reach of Kelani River. Coarse grid atmospheric parameters provided by GCM models for A2 and B2 scenarios of IPCC [1] are downscaled to catchment scale by the application of Statistical Downscaling Model (SDSM). Flood discharge and inundation along the Kelani River reach below Hanwella was analyzed by the application of two-dimensional flood simulation model (FLO-2D). Inflow to the model at Hanwella, is estimated by the HEC- HMS model under future extreme rainfall events. Areas vulnerable for inundation under the above climate change scenarios are presented.

Chemical and Microbial Contamination Status of Ground Water Quality in Kelani River Basin

Water is the key factor in sustaining human life. Water pollution may occur in various formssuch as catchment characteristics, anthropological activities, land use practices and industrialdischarges. Such polluting agents may affect physical, chemical and biological parameters ofsurface and ground water. The present study was focused to analyse the present status ofground water pollution in the Kelani river basin by means of physico-chemical andmicrobiological parameter using standard analytical and microbial methods. Pesticides weredetected using pesticide library in the GCMS. Thirty ground water samples from head,transitional and meandering zones were collected for a period of six months from November2012 to April 2013. pH values of most of the samples were deviated from the SLS drinkingwater standards and remained acidic during the study period (3.98-6.46). 80% of samplesrecorded high COD values (12.81-307.19 ppm) and also showed an increasing tendencytowards downstream of the river basin. High BOD values were detected in meandering zone(4.80-10.19 ppm) in comparison to the head and transitional zones. The conductivity, TDSand hardness values were ranged between 21.67-917.00 μs/cm, 13.37-596.05 ppm, 2.00-206.67 ppm respectively. Acceptable concentrations of phosphate and nitrate were detectedbetween 0.004-0.344 ppm and 0.01-1.394 ppm. Total coliform and feacal coliform countswere almost above 1,100 for 100ml. Samples from head and meandering zone of the riverbasin have shown more than 80% and 100% of total and feacal coliform contaminationsrespectively. Heavy metals such as Cd, Al, Zn, Pb, Cr, Cu remains within the SLS standardsfor drinking water. During the rainy season in some sampling locations of the head andmeandering zone of the river basin, high Cd, Al and Zn were detected, though theconcentrations remain below the SLS drinking water standards. Some pesticides/derivativesnamely O,O-dimethyle S-methylcarbamoylmethyl phosphorodithioate, 5-bromo-3-sec-butyl-6-methyluracil, O,O-dimethyl S-2-(1-methylcarbamoyl-ethylthio) ethyl phosphorothioate, 1-(4-chlorophenoxy)-3,3-dimethyl-1-(1H-1,2,4-triazol-1-yl)-2-butanone were detected in somewells in the transitional zone indicating the effect of anthropological activities on groundwater pollution in the Kelani river basin. The study is in progress to identify and quantifypathogenic microbes contamination in the river basin.

Modeling of Event and Continuous Flow Hydrographs with HEC–HMS: Case Study in the Kelani River Basin, Sri Lanka

AbstractThis paper describes a case study of event and continuous hydrologic modeling in the Kelani River basin in Sri Lanka using the Hydrologic Engineering Center—Hydrologic Modeling System (HEC–HMS). An extremely high rainfall event in November 2005 was used to calibrate model parameters, and extremely high rainfall events in April–May 2008, May–June 2008, and May 2010 were used to validate the event model. The calibrated, direct runoff and base flow parameters were then used in the continuous hydrologic model. The Green and Ampt infiltration loss method was used to account for infiltration loss in event-based modeling and a five-layer soil moisture accounting loss method was employed in continuous modeling. The Clark unit hydrograph method and the recession base flow method were used to simulate direct runoff and base flow, respectively. The results depict the capability of HEC–HMS to reproduce streamflows in the basin to a high accuracy with averaged computed Nash–Sutcliffe efficiencies of 0.91 for e...

Flood Inundation Mapping along the Lower Reach of Kelani River Basin under the Impact of Climatic Change

The downstream low lying region of the Kelani River including the Colombo suburbs, experience severe inundation due to heavy rainfalls in the upper basin of the Kelani River. Occurrence of heavy rainfalls is expected to be more frequent in the tropics with the impact of climatic change (IPCC, 2007). Therefore, understanding future rainfall intensity in the river basin and inundation in the low lying region along the lower reach of the Kelani River is extremely important as this is a region with a high population density and economic activities in the suburbs of the capital. The present study analyses the potential extreme rainfalls and resulting flood inundation along the lower Kelani River. Coarse grid atmospheric parameters provided by Global Climate Model (GCM) models for A2 (high emission scenario) and B2 (low emission scenario) scenarios of Intergovernmental Panel on Climate Change (IPCC, 2007) were downscaled to local scale by applying Statistical Downscaling Model (SDSM). Flood discharge and inundation along the Kelani River reach below Hanwella were analyzed by applying two-dimensional flood simulation model (FLO-2D). Inflow to the model at Hanwella, is estimated by the Hydrologic Engineering Center – Hydrologic Modeling System (HEC-HMS) model under future extreme rainfall events. Areas vulnerable to inundation under the above climatic change scenarios are presented.

Puntius kamalika, a new species of barb from Sri Lanka (Teleostei: Cyprinidae)

Since its first record from the island in 1912, the barb Puntius amphibius Valenciennes has regularly featured in Sri Lanka’s ichthyofaunal inventories. Recent work has shown, however, that the name P. amphibius should be reserved for a species originally collected from Bombay, India, and described by Achille Valenciennes in 1842, now known only from its lectotype. The Sri Lankan fish hitherto known by this name is an undescribed species. Puntius kamalika, new species, is distinguished from all Sri Lankan and peninsular-Indian congeners by having (in addition to a suite of mensural characters) ½4/1/2½ scales in transverse line between mid-dorsal scale row and pelvic-fin origin and lacking any prominent markings on fins and body in both living and preserved examples. The new species is widely distributed in the island’s wet-zone lowlands (rainfall > 2,500 mm yr -1 ), where it occurs in streams, rivers and marshes between the Kelani-River basin draining to the island’s west, and the Gin River basin to the south. It is locally common.