Gin River Research Articles

Projection of climate change effects on flood inundation in the Gin River basin, Sri Lanka

Abstract. Human-induced climate change has altered the frequency and severity of heavy precipitation, droughts, and floods worldwide. Sri Lanka, a developing country in the Indian Ocean, has suffered frequent floods, affecting over 64 % of the population in the past decade. The Gin River, the primary drinking water source of the densely populated Galle district with over 1 million residents, faces recurrent flood disasters. Therefore, this study employed a multi-model ensemble to simultaneously simulate the impact of climate change on both river flow and inundation extent in the frequently flooded Gin River basin located in humid tropical monsoon region. Bias-corrected climate projections of an ensemble of five General Circulation Models (GCMs) from the Coupled Model Inter-comparison Project Phase 5 (CMIP5) under Representative Concentration Pathway (RCP) 4.5 emission scenario were used to project future river flow and flood inundation in the Gin River basin, Sri Lanka. The validated Rainfall–Runoff–Inundation (RRI) model projected a 5 % increase in high flows (flows exceeding a 5 % probability of exceedance (<Q5)) at the downstream (Baddegama) gauging station and a 16 % increase at the upstream (Thawalma) gauging station in the future (2040–2060) in comparison to the past (1980–2000), which can be attributed to the elevated rainfall projected during the two monsoon seasons (southwest monsoon (May–September) and northeast monsoon (December–February)) by the GCM ensemble. In addition to the projected changes in high flows revealed by the RRI simulations, the model also yielded critical information about the expansion of annual maximum inundated extent in the basin by 3.5 % that will aid flood risk projection and sustainable management in the basin.

The Effect of Incorporation of Embankment Information for Flood Simulation of the Gin River, Sri Lanka

As flooding is inevitable and becoming increasingly frequent, efficient flood management strategies should be developed to manage floods, especially in developing countries. Rainfall-Runoff-Inundation (RRI) model, which is based on a diffusive wave model, was applied to Gin River Basin, Sri Lanka using daily rainfall data. The RRI model was calibrated and validated for three past flood events (2003, 2016, and 2017) based on observed discharge data and inundation maps developed from ground survey data and satellite images. The Nash–Sutcliffe efficiency (NSE) values for river discharge obtained at the downstream gauging station were greater than 0.7 during both the calibration and validation experiments. Simulated inundation data showed good agreement with the limited observational records. The Critical Success Index (CSI) value for inundated extent in large flood event (May 2017) within downstream was greater than 0.3. Incorporation of embankment information significantly improved the accuracy of the simulation of inundation extent during large flood events (May 2017). The CSI value without embankment information for large flood event (May 2017) within downstream decreased to around 0.1. On the other hand, the embankment information was less useful for smaller flood events caused by less extreme rainfall. Inclusion of embankment information for large flood events enhanced the model performance, thus ensuring the availability of accurate inundation information for efficient flood risk planning and management in the basin.

Heavy metal pollution in selected upland tributaries of Sri Lanka: comprehension towards the localization of sources of pollution.

This study aimed to assess the heavy metal (HM) profile of the main upland tributaries of three major rivers, the Mahaweli, the Deduru and the Gin Rivers, which are commonly used for urban water supply in Sri Lanka. The HM profiles of arsenic (As), cadmium (Cd), lead (Pb) and mercury (Hg) were investigated by ICP-MS. Land-use classification was performed to locate the main sources of pollution. Mean pH, TDS and conductivity showed significant inter-site mean differences (p < 0.001). The mean contents of the HMs, considering all rivers, were observed in the order [Hg] > [As] > [Pb] > [Cd] at the sources and [As] > [Hg] > [Pb] > [Cd] at the river mouths. Particularly, in the Mahaweli River, the mean As content was 0.08 ± 0.05 μg·L-1 and showed an increasing trend from the source to the river mouth. In the Deduru River, the mean Hg content was 0.14 ± 0.15 μg·L-1, and of all rivers studied, the highest content of 0.50 ± 0.17 μg·L-1 was recorded. The Gin River showed significant inter-site mean differences (p < 0.05) in [Pb], [As] and [Hg]. In all rivers studied, [As] was significantly higher in water samples collected near agricultural lands and urban areas as compared with the other land-use/cover types, which was further proved by a significant positive correlation (coefficient = 0.479, p = 0.0325). We, therefore, emphasized that HM pollution is more likely due to anthropogenic activities in the upper catchment with less lithogenic contamination. However, national water quality management should be further strengthened and new policy enforcement is emphasized.

Prevalence of antibiotic resistance in the tropical rivers of Sri Lanka and India

We evaluate the imprints of urbanization, landuse and lifestyle on the prevalence and provenance of antibiotic resistance in the tropical rivers of Sri Lanka (Kelani and Gin) and India (Sabarmati, and Brahmaputra River). The prevalence of E. coli in the Kelani, Sabarmati, and Brahmaputra Rivers was in the range of 10–27, 267–76,600, and <50 CFU ml−1 respectively. Isolated E. coli colonies were subjected to six antibiotics to assess their resistance. We found higher resistance to old generation antibiotics like tetracycline (TC), and sulfamethoxazole (ST) transcends the resistance for fluoroquinolones like norfloxacin (NFX), ciprofloxacin (CIP), and levofloxacin (LVX). Interestingly, both Indian rivers had exhibited relatively higher resistance to TC and ST than the Kelani river or Gin River, implying that the Sri Lankan situation is relatively less critical. At genetic level the resistance for β-lactams, fluoroquinolones and sulphonamides, were detected in many samples, as reported globally. While the resistance genes for aac-(6’)-1b-cr, qnrS and sul1 were detected in both Sri Lankan and Indian Rivers, blaTEM and ampC were specific to the Indian Rivers only. Decoupling of the prevalence of metal contamination and antibiotic resistance has been noticed in India and Sri Lanka. Study implies that urbanization, landuse, and lifestyle (ULL) are the three most critical factors governing multidrug resistance (MDR) and fecal contamination.

Influence of nearshore sediment dynamics on the distribution of heavy mineral placer deposits in Sri Lanka

Beach sediments in Sri Lanka contain industrial-grade heavy mineral occurrences. Samples of both offshore and onshore sediments were collected to examine the provenance, mineralogy and geochemical compositions of the heavy mineral occurrences. Coastal morphodynamic changes along the coastline of Sri Lanka were analyzed using the time-series satellite images. These coastal morphodynamic changes were used to identify the prominent directions of monsoon-influenced longshore currents, coastal sediment accretion and depositional trends and their relationships to the provenance of the heavy minerals. Results show the concentrations of detrital ilmenite, zircon, garnet, monazite, and rutile vary in the onshore and offshore sediments. The heavy mineral potential of the northeastern coast is high (average contents of about 45–50% in the Verugal deposit, 70–85% in the Pulmoddai deposit, and 3.5–5.0% in offshore samples stretching from Nilaveli to Kokkilai), compared to sediments in southwest (average content about 10% in onshore sediments and 2% in offshore sediments from the mouth of the Gin River). Therefore, no economic-grade heavy mineral placers were identified in the offshore environments. The high concentrations of heavy minerals in beach sediments and low concentrations in offshore sediments suggest operation of a panning system in the surf zone to form enriched placer deposits. Major and trace element compositions of beach sediments show marked enrichments of TiO2, Fe2O3, La, Ce, Zr, Cr, Nb, Th and V compared to average Upper Continental Crust (UCC) values. Analysis of prominent coastal longshore transport patterns identifies bidirectional sediment transport in the northeast coast of Sri Lanka. In the southwestern coast, two transport directions occur with anti-clockwise transport from Galle to Hambantota, and clockwise transport from Hikkaduwa to Wadduwa. The heavy minerals in the placers were mainly derived from Precambrian metamorphic rocks, and transported to the coast through the river systems of Sri Lanka.

Rating curve based assessment of seasonal variability of sulfate in streamflow

Though constituent concentrations and loads in rivers exhibit apparent seasonal fluctuations, they are characterized by event-driven nature of the fluctuations in respond to natural processes and seasonal anthropogenic activities. This study aimed at establishing relationship between streamflow and sulfate load in Gin River, the major water source in southern Sri Lanka and assessing seasonal sulfate levels in the streamflow following monsoon pattern and cultivation seasons. Rating curve, a load-streamflow regression model, was developed using adjusted maximum likelihood estimation. Following the assumptions of model fit, the regression model showed low correlation among explanatory variables and good empirical agreement with the measured data exhibiting its applicability to deduce sulfate loads from streamflow data, during non-sampling periods. Sulfate loads, highly dependent on streamflow, peaked annually in April-June (south-west monsoon contributing to Yala cultivation season) and October-December (north-east monsoon contributing to Maha cultivation season), following the bimodal monsoon pattern in the catchment. Median sulfate load exhibited fourfold increase from the lowest value 8,888kg/day in August (non-cultivation season) to the highest value 38,185kg/day in November (Maha cultivation season), despite the twofold increase of median streamflow between the twomonths. Flow-weighted sulfate concentrations showed varying flow dependence attributed to the seasonality. At low streamflows (above 70th percentile), sulfate concentration and streamflow were inversely related and at high streamflows (below 30th percentile), and sulfate concentration and streamflow were directly related. Elevated sulfate concentrations attributed to less soluble sulfate irons were clearly evident during the two cultivation seasons which coincided with the monsoon periods.

Stream Flow Modeling In Gin River Basin Using Swat Cup

Around the world, human activity and natural forces are reducing available water resources. Rivers play a vital role to provide the water requirements of humans and nature. The stream flow of a river is affected by both natural and human factors. River (stream) flow is generally simulated by using mathematical models, and they can be used to evaluate the response of rivers to changes in flow parameters. River Gin Ganga in the south of Sri Lanka, draining an area of 865.5 km2, is subject to rapid changes in land use apart from climate variability. In order to simulate the stream flow of Gin Ganga a SWAT (Soil and Water Assessment Tool) model (consisting of 43 sub-basins) was set-up, calibrated and validated. The model is calibrated (1983-1989) and validated (1990-1994) against monthly measured discharge at one location by using Sequential Uncertainty Fitting version 2 (SUFI-2) techniques. The performance of the calibration was evaluated using five objective functions including the coefficient of determination (R2), Nash-Sutcliff (NS) efficiency P-factor, R-factor and coefficient of determination divided by coefficient of regression (bR2). The model simulates the stream flow for 22 years. The Curve Number (CN2) parameter of the model was identified as the most sensitive and critical parameter (which had a positive correlation with runoff) for model calibration. The calibrated model may be further improved with measured river discharge data at other locations (if and when available). The model can be further used for analyzing: impacts of climatic and land use changes, sediment yields, water quality and flood risk. Keywords: Gin Ganga, Modelling, Stream flow, SUFI-2, SWAT

Suspended Sediment Concentration and its Impact on Aquatic Invertebrates in the Gin River, Sri Lanka

Understanding the level of suspended sediment is important for the management of aquatic fauna and flora. This study focused on the impact of suspended sediment concentration (SSC) on aquatic invertebrates in the basin of Gin river, Sri Lanka. Sixteen sampling locations along the river basin were used for data collection. Water temperature, dissolved oxygen, pH, electrical conductivity, turbidity and SSC were determined using standard laboratory methods. Aquatic invertebrates were collected using Kick sampling and stone lifting methods and they were identified using keys. Statistical analyses were done by Principal Component Analysis, factor analysis and descriptive analysis techniques. The water temperature and dissolved oxygen concentration in the Gin river basin were 25.76 ± 2.4 °C and 6.85 ± 6.1 mg/l (mean ± SD), respectively. The mean turbidity in the basin was 10.09 ± 16.1 NTU (mean ± SD). The SSC increased towards middle and lower catchments. Thirty nine different aquatic invertebrate taxa were recorded. A higher diversity of aquatic invertebrates was recorded with lower SSC in upper catchment. A negative relationship was evident between SSC and number of aquatic invertebrate species. High SSC had a negative impact on aquatic invertebrate diversity in the Gin river basin. A positive correlation was present between SSC and turbidity and therefore, a model was developed to predict SSC using turbidity data.

Impact of Land Use on Surface Water Quality: A Case Study in the Gin River Basin, Sri Lanka

Impact of Land Use on Surface Water Quality: A Case Study in the Gin River Basin, Sri Lanka

Anthropogenic impacts on vegetation diversity and spatial floral composition of the swamp forest associated with the tropical river basin

The Gin river wetland marsh has been identified as one of the most dynamic ecosystem in Sri Lanka, providing habitats for associated floral and faunal communities under a permanent or temporary accumulation of water. Study was focused to understand the structure, composition and threats of the Ginthota wetland marsh, by identifying the biodiversity distribution, anthropogenic activities and evaluation of water quality changes. Vegetation was sampled in randomized plots and water samples were collected in the three sampling locations. Fifty seven species of plants of twenty three different families were identified. Out of them, forty eight species were native and five were introduced. Argyreia populifolia was identified as an endemic species. Three plants were identified as dominant plant species Sonneratia caseolaris, Annona glabra and Acrosricum auriyam. Annona glabra was an invasive species and Nypa fruticans was an endangered species. The Shannon-Wener Index for the disturbed and undisturbed areas was 0.685 and 1.721 respectively, reflecting a higher biodiversity in the undisturbed areas. Many anthropogenic factors are causes for the deteriorating diversity and also water quality.

Projecting turbidity levels in future river flow: a mathematical modeling approach

Climate and land use change impacts on river flow were evaluated in this study with emphasis placed on turbidity. Turbidity levels for the year 2020 were projected for Gin River, one of the prime sources of drinking water in Southern Sri Lanka. Future land use in the Gin catchment was predicted using a GIS based statistical regression approach. Regional Climate Modelling system generated the future rainfall for the SRES A2 and SRES A1B emission scenarios. Streamflow simulations were carried out using a distributed hydrologic model, and turbidity values were determined using rating curve based relationship developed between river discharge and TSS (Total Suspended Solid) concentration followed by Turbidity-TSS linear regression correlation. Increased turbidity levels are clearly evident under the SRES A2 scenario, following more pronounced increased stream flows. Projected 75th percentile monthly turbidity values in year 2020 are expected to increase during May to November compared to the baseline, and in certain months, about 100%increase is noted. 60% of the time, year 2020 turbidity levels have indicated exceedance of the water quality standards set for the potable water as well the inland waters of Sri Lanka, which would lead to exert extra challenge on future drinking water production in Southern region of Sri Lanka. ENGINEER, Vol. 48, No.01, pp. 61-70, 2015

Range extension of Perbrinckia scansor (Crustacea) in Sri Lanka

Perbrinckia scansor (Ng, 1995) is the only known tree-climbing freshwater crab among the 52 freshwater crab species of Sri Lanka. According to published literature, this endemic species was recorded in eleven localities (elevation range 150–960m a.s.l) in the Kalu, Walawe and Gin River basins and assessed as “Least Concern”, but again this species was categorised as Endangered. This species is a habitat specialist with adults living in rainwater-filled phytotelms from about ground level up to 1 m above ground. We recorded the distribution of P. scansor from 47 localities through opportunistic observations within the period 2005–2010.

Prediction of ungauged river basin for hydropower potential and flood risk mitigation: a case study at Gin River, Sri Lanka

A hydrologic study was performed for ungauged river basin of Sri Lanka to examine synthetic discharge relations. Rainfall-runoff relationships were used for identifying hydrological conditions of the Gin River basin. The peak discharge achieves within 4.74 hours from the onset of the rainstorm and 11.95 hours take to reach its normal discharge conditions. Stream frequency of the Gin River is 4.56 junctions/km2 while the channel slope gradient is 7.90 m/km. The regional coefficient of the catchment is 0.00296. Higher stream frequency and gentle channel slope were identified as flood triggering factors of the basin. Mini-hydropower systems were recognised as the most applicable and economical flood controlling hydraulic structures. Also, it can be utilised as a reliable energy source (8,630.0 kW).

Streamflow, Suspended Solids, and Turbidity Characteristics of the Gin River, Sri Lanka

"ENGINEER", established in 1973 by The Institution of Engineers, is a Journal for dissemination of Engineering knowledge, published quarterly.Cover DescriptionCover images show a schematic diagram of a Pumped-Storage Hydroelectricity (PSH) facility and one of the promising sites for PSH in Sri Lanka. The latter image was obtained from the publicly available JICA report on “Development Planning on Optimal Power Generation for Peak Demand in Sri Lanka”. The Institution of Engineers, Sri Lanka acknowledges JICA for the image.If you are interested in contributing an Original Technical Paper based on research by the author(s) (intended for Section I) or an Original Article of Professional or Technical interest related to Engineering. (Section II) to this journal please go through the publication checklist which can be downloaded from here.

Variation of constituent loads and concentrations with the flow in Gin river, Sri Lanka

The Journal of the National Science Foundation of Sri Lanka publishes the results of research in all aspects of Science and Technology. The journal also has a website at http://www.nsf.gov.lk/. 2021 Impact Factor: 0.682The JNSF provides immediate open access to its content on the principle that making research freely available to the public supports a greater global exchange of knowledge.Cover :Leatherback (a), green (b - adult &amp; f - hatchling), hawksbill (c) and olive ridley (d) turtles who nest in Sri Lankan beaches, green turtle crawl marks (e) and by-catch of sea turtles in fisheries (c &amp; d)Photo credits: SJ Perera (a &amp; c), WPN Perera (b &amp; e), K Ekaratne (d &amp; f)

Applicability of global public domain data versus local detailed data for distributed hydrological modelling: a study form Gin river basin Sri Lanka

This study investigates the applicability of global public domain data versus local detailed data for distributed hydrological modelling using a case study approach. Major hydrological characteristics in Gin river basin are simulated in the study by applying the distributed hydrological model, YHyM/BTOPMC (University of Yamanashi Distributed Hydrological Model with Block-wise use of TOPMODEL and Muskingum-Cunge method) utilizing the global public domain data sets (Case 1) and local detailed data sets (Case 2). Evaluation of the model outputs for Case 1 and Case 2 shows that the overall hydrological behavior of the Gin river basin is adequately simulated by the model for both Case 1 and Case 2. The simulated average annual discharge volumes in Case 1 and Case 2 at Agaliya during 2002–2006, vary from the observed average annual discharge volume by +4.25 and +1.31 %, respectively. In general, simulated daily discharge in Case 1 shows slightly higher value than that of Case 2 resulting a difference of 0.9 m3/s during 2002–2006, on average. The relative differences between the simulated daily discharges in Case 1 and Case 2 become higher during the recession limbs of the flow hydrographs at Agaliya. Reasons for these variations are being discussed in the study. The results of the study give motivation towards the use of global public domain data for hydrologic simulations in data-poor (limited availability of local data) basins.

Distribution patterns of the genus &lt;i&gt;Paludomus&lt;/i&gt; (Gastropoda: Thiaridae: Paludominae) in Mahaweli, Kelani, Kalu, Gin and Maha-Oya river basins of Sri Lanka

Since the publication of Preston’s Fauna of British India – Freshwater Gastropoda and Pelcypoda in 1915, a vast amount of knowledge has accumulated on the fresh water molluscs. Starmuhlner (1974) published a monograph on the fresh water gastropods, in which he listed 31 species of freshwater snails from Sri Lanka. Until the early 20th century, malacologists used mainly conchological characters to describe species. However, the shells of freshwater gastropods are highly variable, show ecological plasticity, and are known to suffer from convergence and homoplasy, and therefore do not always reliably reflect systematic boundaries. It is already known that other groups of freshwater organisms in Sri Lanka including fish and crabs show high levels of endemism within individual river basins. It remains to be discovered whether molluscs too, show such basin-level endemism. These studies also found that there was significant altitudinal stratification and basin-level endemism of species, a factor that remains to be assessed for aquatic molluscs. In order to address these questions, and assess the diversity of this fauna, we surveyed the freshwater mollusc fauna (focusing mainly on the genus Paludomus) in the Mahaweli, Kelani, Kalu, Gin and Maha-Oya River basins of Sri Lanka. A total of 10 morphospecies were recorded, based on examination of 20 specimens of each species from 20 locations in the altitude range 100-2000 m above mean sea level. Species-level identification is in progress, and further surveys are needed to assess the full diversity of this important fauna.

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 &gt; 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.