Research Papers - Department of Civil Engineering
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Publication Open Access Postharvest ripening and respiration of chili(University Of Ruhuna, 2004) Chaturani, G. D. G; Wilson, S; Perera, S. V. T; Hettiarachchi, M. PEffect o f exogenous ethylene application on postharvest ripening and respiratory pattern o f chilli (Capsicum annum Var.MI-2) harvested at different stages o f maturity was examined. Chillies harvested at mature green and colour break stages were used fo r the ripening study. Pods were allowed to ripen at ambient conditions (32 ± 2 °C and 37% RH) with 0, 100, 200, 300, and 400ppm ethylene concentrations. Observations were made on colour development and weight o f red ripe pods during storage period. Ethylene treatment had no significant effect on colour development o f chilli harvested at both stages o f maturity. Fruits harvested at different stages o f maturity ranging from light green to fu ll red were usedfor the respiration study at 12.2 °C and 83 % RH in a closed system. Respiration rates o f chilli from light green to fu ll red stage ranged between 12.7-24.2 mgCO/kg/h. The rate o f respiration was low at light green stage and increased with maturity reaching a peak (24.2 mgCO/kg/h) at colour break stage. Respiration rate decreased with fru it ripening and increased with development o f full red colour. The internal ethylene concentration o f pods was ranged between 3.2-4.3 ppm. However, there was no ethylene peak observed with the maturity.Publication Embargo Iron and manganese removal from textile effluents in anaerobic attached-growth bioreactor filled with coirfibres(IWA Publishing, 2007) Jayaweera, M. W; Gomes, P. I. A; Wijeyekoon, S. Lt A laboratory scale study on Fe and Mn removal in upflow anaerobic bioreactor of a working volume of 20 L with coir fibre as the filter medium was investigated for a period of 312 days. The maximum Fe and Mn levels considered were 10 and 5 mg/L respectively, which are the typical average values of textile effluents subsequent to the primary and secondary treatments. Ten sub-experimental runs were conducted with varying HRTs (5 days to 1 day), ratios of COD:SO22 4 (20 to 3.5), Fe levels (0.005 to 10 mg/L) and Mn levels (0 to 5 mg/L). COD:SO22 4 of 3.5 was identified as the optimum point at which sulphate reducing bacteria (SRBs) out competed methane producing bacteria (MPBs) and further reduction of this ratio caused total and/or significant inhibition of MPBs, thus building sulphate reducing conditions. The effluent contained Fe and Mn below the permissible levels (1.6 and 1.1 mg/L for Fe and Mn, respectively) stipulated by US National Pollution Discharge Elimination System (NPDES) for inland surface waters at HRTs higher than 3 days. Results of the mass balance showed more Fe accumulation (60%) in sediments whereas 27% in the filter media. An opposite observation was noticed for MnPublication Embargo Spatial and temporal heterogeneity of Eragrostis curvula in the downstream flood meadow of a regulated river(EDP Sciences, 2009) Gomes, P. I. A; Asaeda, TWe studied the spatiotemporal trends of Eragrostis curvula (Schrad.) Nees in a flood meadow of a regulated river. The response variables, including the abundance of colonies, colony sizes, flowering spikes, biomass and root structure were checked against a set of environmental variables. These variables included distance from the river, substrate conditions (stony to sandy), soil nutrients (total nitrogen, phosphorous and calcium) and soil moisture. Relationships were evidenced using redundancy analysis. Response variables were found to be distinctive and based on substrate conditions (i.e. stony or sandy). The variables ‘distance from the river’ and ‘soil phosphorous’ contributed significantly to the overall variance. Stony habitats were observed to have lower soil nutrient levels and were characterised by monospecific stands of E. curvula, while the high nutrient levels of sandy habitats promoted heterogeneous herbaceous vegetation growth. Primary production, especially belowground, was measured to be significantly higher (t-test, P<0.05) in stony habitats. Spatiotemporal trends suggested that, irrespective of the number of colonies, E. curvula demonstrated significant levels of adaptation to micro-environments through biomass allocation and the morphological plasticity of its roots. The study results suggest that river regulation and the subsequent reduction in the frequency of inundation, in addition to the reduction of nutrients and fine sediment supply downstream, give a competitive edge to E. curvula over other herbaceous species.Publication Embargo Phycoremediation of Chromium (VI) by Nitella and impact of calcium encrustation(Elsevier, 2009-07-30) Gomes, P. I. A; Asaeda, TThis article discusses the applicability of the Charophyte, Nitella pseudoflabellata in the remediation of Cr (VI) contaminated waters at different calcifying potentials. Its growth was found to be positively correlated with Ca in water (CaW), but marginally significant in the presence of Cr (VI) in water (CrW). High CaW resulted in calcite encrustation on the plant cell wall. CaW was found to be aiding Cr (VI) fixation in the long run, as this correlated positively with both CaW and CrW. However, Ca interfered with passive Cr (VI) accumulation in live plant matter at low CrW concentrations (≤0.2 mg/L). Biosorption by dead plant matter seemed to be the major mechanism as the dead plant organs contained >1 mg/g Cr dry weight of plant. Cr (VI) concentrations greater than 0.4 mg/L were too toxic, showing maximum quantum efficiency of PSII photochemistry (Fv/Fm) values < 0.63. The opposite was noticed (Fv/Fm > 0.76) when Cr (VI) was less than 0.2 mg/L. Elongation curve patterns based on shoot lengths showed similar scenarios. In all cases high CaW units with calcite encrustation found to be least affected by Cr (VI) toxicity. Optimum remediation was obtained using a combination of high Ca and Cr (VI) in the case of passive (short-term) operation and low Ca and Cr (VI) for active (long-term) operation. Under the passive scenario, plants accumulated above 1.2 mg/g Cr dry weight whereas in the active case, accumulation was 0.8 mg/g Cr dry weight. We conclude that Nitella-mediated Cr (VI) remediation is a promising technique within the range and conditions investigated.Publication Open Access Entrance zone effect on the sediment trapping efficiency in desilting tanks of run-of-river type mini-hydropower plants(The University of Peradeniya, Peradeniya, Sri Lanka, 2007-11-30) Rathnayake, U. S; Harishchandra, M. R. T. S; Weerakoon, S. BDevelopment of run-of-river type minihydropower plants is receiving increased attention in Sri Lanka at present owing to the incentives announced for developers of renewable power generation projects during the last decade by the Sri Lankan government. The sources for most of the run-of-river type mini hydropower plants are mountainous streams where the discharges experience significant seasonal variation with frequent flash floods. The catchments of these streams are generally steep and face an increasing trend of soil erosion due to cultivation and other human activities. Therefore, the stream flows carry high sediment loads during seasonal floods. This sediment-laden flow enters the headrace canals feeding water to the turbines of the rninhydropower plants. Sediment in the water passing through the turbines with high velocity erode the contact surfaces of turbine components. The erosion of turbine components leads to a drop in hydraulic efficiency and to a high maintenance cost of the turbines. Removal of sand carried with the flow in the headrace canals of run-of-river mini hydropower plants is therefore an important issue for the developers to reduce the maintenance cost of the turbines (Singal and Ranendra, 2006). Introduction of a de-silting tank in series with the headrace canal is one of the commonly used techniques for this purpose. De-silting tanks are designed as settling basins to settle sediment greater than a targeted size (Janssen, 2004). The shape and the size of the de-silting tank are major factors affecting the sand trapping efficiency of the desilting tank. Several empirical and semiempirical relations for the efficiency of …Publication Open Access Theoretical analysis for the interaction between the river flow and the seepage flow(Proceedings of the 6th WSEAS International Conference on FLUID MECHANICS, 2009) Rathnayake, U. S; Izumi, NMany previous studies have been carried on the interaction between river flow and the seepage flow in the environmental point of view, but these hardly touch on the boundary conditions or the limitations for the interactions. The subsurface layer below the river is known as the hyporheic layer and it is a saturated band of sediment that surrounds river flow and forms a linkage between the river and the aquifer. The large velocity difference between the river flow layer and the seepage flow layer causes the instability of the flows. Due to this flow instability, a reciprocating flow motion is generated between the hyporheic layer and the above. Linear stability analysis technique is used to understand the stability of the natural flows in rivers as well as the flows occurred in the air by many researchers. In this study a linear stability analysis is carried out to presents the interaction between the river flow and seepage flow. Reynolds averaged Navier-Stokes equations and Brinkman-Forchheimer equations are used in order to formulate the river flow and seepage flow interaction. The open channel flow is analyzed by mixing length turbulent model and Spectral collocation method incorporated with the Chebyshev polynomials are used to perform the numerical solution of the perturbed equations. Instability diagrams are discussed with several slopes of the layers against the dimensionless particle diameter and wave numbers. It has been noted that the instability occurs even in the range of small dimensionless particle diameter with relatively high wave numbers if there is a seepage layer beneath the flow and the instability region increases with the slope when the wave numbers are at small values.Publication Open Access Flood modeling in the Mahaweli River reach from Kothmale to Polgolla(University of Peradeniya, 2007) Rathnayake, U. S; Weerakoon, S. B; Nandalal, K. D. W; Rathnayake, UThe occurrence of floods and inundation of the low lands adjacent to the Mahaweli River reach from Gampola to Polgolla were very frequent prior to the Kotmale reservoir project in mid 1980s. However, during last two decades with the construction of the Kotmale dam, the regulation of flow by the reservoir has reduced the inundation risk of these lands, which were vulnerable to frequent flooding. As a result, these lands are developed at an increasing rate and more people have started to live in them. This fact gives an alarming signal to the authorities, as the damage that might be caused due to an extreme flood event could be significant. It is therefore of paramount importance that comprehensive flood modeling and inundation analysis of the Mahaweli River reach between Kotmale and Polgolla is carried out. This paper presents the flood modeling and inundation analysis in the Mahaweli river reach from the Kotmale dam to Polgolla barrage using the HECRAS model. The HECRAS model was set up for the river reach using the river cross-sections at 200 m intervals from Kotmale dam to Polgolla barrage. The model was applied to estimate the water stages along the river reach for the floods of different return periods. Though the Kotmale reservoir acts as a flood control reservoir for floods of medium return periods, it becomes ineffective to reduce the flood levels in the downstream flood plains due to floods of high return periods when it has to release high discharge. Inundation areas in the downstream of the dam due to several flood discharges are presented.Publication Open Access Effect of the entrance zone on the trapping efficiency of desilting tanks in run-of-river hydropower plants(Department of Civil Engineering, University of Peradeniya, Peradeniya, 2007-10-22) Weerakoon, S. B; Rathnayake, U. SRun-of-river mini hydropower plants are generally installed in mountainous streams where the catchments are generally steep and vulnerable to high soil erosion. Seasonal heavy rains, especially in tropics and monsoon regions produce large sediment yield from these catchments and the streams experience high sediment concentrations during seasonal floods. Therefore, removal of sand entering into headrace canal in run-of-river mini hydropower plants is an important issue in the run-f-river mini hydropower schemes to reduce the erosion of turbines and other components in contact with water. The desilting tanks constructed in series with the headrace canal play an important role here. The shape and the size of the desilting tank are major factors on the sand trapping efficiency of it. This paper presents a series of laboratory experiments carried out to investigate the effect of the entrance zone on the sand trapping efficiency of the desilting tanks using a scale model of a desilting tank with varying entrance expansion angles. The sand trapping efficiency is found to vary from 50% to 85% with the reduction of espansion angle from 30o to 10o .Publication Open Access Evaluation of the recovering process of Phragmites australis after cutting by the dynamic regrowth model and the validation by the observation(Ecology and Civil Engineering Society, 2004-03-30) YUTANI, K; ASAEDA, T; TANAKA, N; KARUNARATNE, SMowing is a general reed bed management method for the restoration of devastated wetlands and the maintenance of plant diversity in wetlands. Based on the reed growth model that has been developed in recent years, the reed reed length model as a wetland management method Was developed based on the observation results. In the wetlands of Akigase Park in Saitama City, Saitama Prefecture, three years of observations were carried out to investigate the recovery process of reed beds from cutting. Although it had the most adverse effect on the growth of Phragmites auspicus, the proportion of leaves of regenerated shoots after cutting was increased from 0.28 to 0.56 for June and July cutting. June cutting reduced shoot height and dry weight and rhizome dry weight. On the other hand, Yoshi recovered from summer cutting in about 2 years, and reed bed management was performed every 1 or 2 years. The improved reed-cutting regeneration length model, which was shown to be necessary, well reproduced the observation results and the data from the previous literature regarding cutting and field burning. As a result of model calculation, the reeds that grow in a well-nourished environment It was shown that it recovers from cutting in about 3 to 4 years, but it may take 10 years or more for reeds that grow in poorly nourished environments.Publication Open Access Colour-based estimation of rhizome age in Phragmites australis(Kluwer Academic Publishers, 2004-10) Karunaratne, S; Asaeda, T; Toyooka, SThe colour of different age groups of Phragmites australis (Cav.) Trin. ex Steudel rhizomes was studied from April through October 2000 at approximately one-month intervals to propose a more efficient method to identify the rhizome age based on the Munsell colour-order system. Seven rhizome age-classes were recognized, from <1 to 6 years old, based on descriptions published in the scientific literature. During April and May sampling, spectral reflectance between 400 and 700 nm of different rhizome ages was measured at 10 nm intervals, using a spectral colorimeter. Rhizomes of different ages were assigned colours by selecting one/two shortest Euclidian distances between the mean spectral reflectance of each rhizome age category and the Munsell colours on the four-dimentional subspace, made by Principal Component Analysis of the spectral reflectance data of 1289 Munsell colours. The Munsell colour for new to six-year-old rhizomes changed from yellow to yellow-red, and the value decreased from new to six-year-old rhizomes, indicating a darkening with ageing. The age of rhizomes collected from April through October was estimated using the colour key, in addition to the age attribution based on branching hierarchy. Between 87% and 100% of the rhizomes attributed to a certain age class based on branching hierarchy were assigned to the same age class using colours during all sampling dates. There was a strong correlation (r = +0.96) between rhizome age estimated by branching hierarchy and colour. At each sampling, bulk density, an indicator of rhizome storage levels, measured as a verification of age identification, varied among the age categories indicating distinct differences in storage levels. These results confirmed that rhizomes of a specific age category could be assigned a distinct colour, which remains more or less unchanged throughout the growing season. Thus, colour can be used as a primary criterion in the estimation of the age of P. australis rhizomes.