Research Papers - Department of Civil Engineering
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Publication Open Access Comparison of Cell-In-Series and Meso-Scale Physical Habitat Sampling for the Interpretation of Spatiotemporal Variation of Stream Water Quality(IAHR-HK Student Research Forum, 2012-11-17) Gomes, P. I. A; WAI, O. W. HAlthough scale dependence of ecological patterns is conceptually recognised, the studies involving quantitative assessments are rare and rudimentary. Here we evaluate spatiotemporal variation of water quality using two sampling scales (approaches): cell-in-series (CIS) and meso-scale physical habitats (MPH). CIS has its origins in probabilistic sampling and relatively simple. It also reported to be suitable for streams with advective transport. MPH approach is relatively novel for water quality assessments and it considers medium scale morphological units such as pools, riffles, glides, etc. for sampling. Sampling was carried out in the short and steep Tseng Lan Shue stream, during Spring and Summer of 2012. The stream is subject to regulation and various anthropogenic inputs, but with irregular occurrence. For each season, observations were carried out during periods with no influence of severe weather events (typical state) as well as after a rainfall (flushed state). The response variables including water chlorophyll, turbidity, dissolved oxygen, nitrate, nitrite, ammoniacal nitrogen and soluble reactive phosphorous were checked against a set of hydro-environmental variables. These included: stream velocity, width, depth, and slope, bankfull dimensions, and substrate conditions. Relationships among variables were evidenced using redundancy analysis. In general, the water quality parameters showed an irregular variation in the longitudinal direction of the stream. Response and hydro-environmental variables based on two best axes showed a 41% of variance in spring response data in the MPH approach. For CIS it was around 44%. But in flashed floods these were observed to be 60% and 35 % for MPH and CIS, respectively. Similar trend was observed in summer where explanatory power based on CIS was higher for typical state but otherwise for the flashed state. Furthermore, significant environmental variable(s) for respective cases changed with the scales being used: substrate conditions for CIS and stream width and slope for MPS. This study shows that MPH approach is more suitable than CIS as a modelling tool when the stream has less anthropogenic loads. We conclude that the explanatory powers of the MPH and CIS scales (approaches) could be useful in providing a quantitative definition on identifying a “pristine stream”.Publication Embargo Deflectors to introduce heterogeneity to canals(2017 6th National Conference on Technology and Management (NCTM, SLIIT, 2017-01-27) Randima, W. A. H; Wijethilaka, M. A. D. K; Kumara, G. H. V. S; Gomes, P. I. ACanals are manmade lotic water systems constructed for flood control, navigation, irrigation, etc. In general, canals are eco-hydrologically homogeneous. As such, a canal might have the same prismatic cross section and an even bed profile along its course. Such characteristics do not support rich biota, something a sustainable society expects. Several past studies have attributed heterogeneity to be an important factor for a healthy stream. In this study the deflectors were used to introduce the heterogeneity in canals. In tandem studying flow complexity by deflectors, their role with respect to sediment (sand) and seed transport, and fisheries were also studied. The model canal's (laboratory flume) homogenous velocity of 0.4 m/s changed to a range of values from 0.1 to 0.7 m/s after placing deflectors. Similarly, water depth changed from a uniform 30 mm to a range from 20 mm to 70 mm. This resulted in formation of flow patches similar to flow patches formed by meso-scale physical habitats such as pools and riffles. Sediment deposition was patchy and seemed to be stable as only a minor bedload movement was observed for prolonged durations. This meant it is possible to achieve a quasi-equilibrium state in field canals where upstream brings sediments. Seed trapping was weak for floating type seeds, whereas non-floating seeds managed to get deposited with sediment. Fishes quickly migrated to the pool like areas that resulted from deflectors. The results suggested the role of deflectors in transforming a homogenous channel to heterogeneous channel that has the potential to have rich biota which is essential in ecological rehabilitation works.Publication Embargo Eco‐hydraulic evaluation of herbaceous ecosystems below headwater dams without a base flow: Observing below dam reaches as new stream sources(Wiley Online Library, 2017-01) Gomes, P. I. A; Wai, O. W. H; Yan, X. FThe roles of headwater streams are usually underestimated and inadequately managed compared with the larger downstream river systems. This two and half-year study covering several wet and dry seasons evaluated the impacts of small headwater dams without a base flow on downstream herbaceous dynamics. Results showed herb aerial cover and diversity below dams (new stream sources) are unique and different to original stream sources as well as to a comparable unregulated reach. The geomorphological habitats formed subsequent to damming did not show major influence on aerial cover of herbs; nevertheless, diversity showed a clear dependence. Downstream of dams were dominated by Acorus gramineus, which had >40% aerial cover, and this figure increased up to 60% within 2 years (in between a major flood event). Simultaneously, downstream herb diversity decreased by 33%. However, diversity and aerial cover of the unregulated reach and original sources remained more or less the same. Herb pulling tests (simulating an uprooting mechanism during a flood) showed A. gramineus can withstand an eightfold higher force than the other herbs, especially in concrete surfaces and rock/sand pools. The estimated shear force on bed during the major flood was several folds less than the observed. This suggests downstream of dams behave opposite to the conventional understanding that large floods are considered as an agent of restoration.Publication Embargo Ecohydrologic structure and function of stream networks with earthen upstream and concrete-lined downstream(Wiley Online Library, 2019-06) Gomes, P. I. A; Wai, O. W. HConcrete-lined streams are one of the most extreme forms of river regulation. This study investigated an urban stream network with concrete-lined (C) and earthen (E) sections. The C sections were positioned downstream of the E sections. This abrupt change of stream type due to concrete lining was compared with the predictions of river continuum concept and process domain concept. River continuum concepts predictions on the macroinvertebrate functional feeding group fractions against stream order and energy sources showed disagreements in this study. Furthermore, other than abundance of pollution intolerant species variation, most of the species responses did not support the process domain concept predictions. Correlations between explanatory variables (stream hydraulics or water quality) and response variables (macroinvertebrate composition and vegetation) observed to be dependent on stream lining and seasons. Stream discharge showed positive correlations with the pollution representative species in both section types but was more obvious in C sections. Water budget estimations showed that wastewater accounted for at least 5% of stream discharge of the C sections in the dry season. pH was the most important and significant water quality parameter of the C sections. Against expectations, nitrogen species and soluble reactive phosphorus did not have a major impact on species variables. Hydraulic variables that represented stream heterogeneity were more useful in explaining species variables of the E sections. Similar explanatory powers by the hydraulics and water quality variables of the C sections demonstrated the importance and interdependency of stream hydraulics and water quality in rehabilitating of this unique ecosystem.Publication Open Access Assessment of pollution sources, fate of pollutants, and potential instream interventions to mitigate pollution of earthen canals of urban to rural-urban fringe(Springer International Publishing, 2019-11) Gomes, P. I. A; Fernando, B. A. V. W; Dehini, G. KThree representative earthen canals from urban, peri-urban, and rural-urban fringe of Sri Lanka were studied for a 2-year period against different seasons to capture insights important in ecological rehabilitation. Only the canal from rural-urban fringe showed a better water quality in wet season; elucidating, the impact of contaminated catchment runoff in the other canals. At a given sampling session, one or two peaks (relative maxima) were observed in urban and peri-urban canals for pollution representative parameters such as nitrate nitrogen and soluble reactive phosphorus. Those peaks were highly localised, an indication of poor advection. In general, two-dimensional variations of electrical conductivity and turbidity in dry season were uniform in urban and peri-urban canals, an indication of dominant molecular diffusion. This was further evidenced via physical models for different flow stages (low, high, and bankfull). Therefore, fate of contaminants had to be mainly governed by assimilation via sediments. However, grey water footprint analyses showed urban and peri-urban canals have over utilised the natural assimilation capacity of many water quality parameters by several folds. This study proved the importance of inducing attenuation by instream physical heterogeneity similar to natural streams or naturalised canals such as the canal from the rural-urban fringe of this study.Publication Open Access A geo-spatial database about the eco-environment and its key issues in South Asia(Taylor & Francis, 2018-07-03) Li, A; Deng, W; Zhao, W; Liu, B; Zhang, J; Kong, B; Nan, X; Bian, J; Koirala, H. L; Gilani, H; Sati, V. P; Gomes, P. I. A; Khanal, N. RThe South Asia has high variability ingeographical features, climate,and landscapes. With the rapid economic development and populationgrowth, the increased pressure on natural resources, land degradation,water crisis, and climate change become the common concerns for thecountries in the region. To get a deep and general idea about the landand water natural resources and environment in South Asia, a knowl-edge database was constructed based on the climatic condition, landuse/cover, water resources, water disasters, and geohazards. The resultspresented a scientific insight regarding the spatio-temporal changingpattern of the eco-environmental components in this region. Riskassessments were performed for thefloods, droughts, and geohazardswhich occurred with a high frequency. In general, the big knowledgedatabase established in this study would be helpful to aid the devel-opment of future policies and programs (like the Belt and RoadInitiative) for environmental issues adaptation in the region, includinginitiatives for regional cooperation and capacity building in naturalresources and environment managementPublication 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 In‐stream physical heterogeneity, rainfall aided flushing, and discharge on stream water quality(Water Environment Federation, 2015-08) Gomes, P. I. A; Wai, O. W. HImplications of instream physical heterogeneity, rainfall-aided flushing, and stream discharge on water quality control have been investigated in a headwater stream of a climatic region that has contrasting dry and wet seasons. Dry (low flow) season's physical heterogeneity showed a positive correlation with good water quality. However, in the wet season, physical heterogeneity showed minor or no significance on water quality variations. Furthermore, physical heterogeneity appeared to be more complementary with good water quality subsequent to rainfall events. In many cases stream discharge was a reason for poor water quality. For the dry season, graywater inputs to the stream could be held responsible. In the wet season, it was probably the result of catchment level disturbances (e.g., regulation of ephemeral freshwater paths). Overall, this study revealed the importance of catchment-based approaches on water quality improvement in tandem with in-stream approaches framed on a temporal scale.Publication Embargo Relationships among anthropogenic disturbances representative riparian and non-riparian herbaceous indicators (biomass and diversity), land use, and lotic water quality …(Springer International Publishing, 2014-09) Gomes, P. I. A; Wai, O. W. H; Kularatne, R. K. A; Priyankara, T. D. P; Anojika, K. G. M. S; Kumari, G. M. N. RThis study was carried out to evaluate the linkages among herbaceous plant biomass (i.e., aboveground and litter biomasses) and diversity (ShannonWiener index) in riparian and non-riparian areas, land use, and lotic water quality (which included first- and second-order natural streams, a canal, and a reach of a lowland river). Herb stands selected were free from anthropogenic disturbances such as farming and construction activities for a period of 3 years (this was the dominant and peak frequency of disturbances of the study area). The results suggested that herb indicators are good representatives of the land use. However, land use explanations for herb indicators were complex and not universal for all lotic waters. The correlations between herb indicators and water quality were strong for the low-order natural streams. In these streams, herb indicators explained >36 % of the total variation with several statistically significant herb indicators. However, the large river section showed weak correlations. Furthermore, the canal’s hydrology (connectivity to sea) seemed to be more influential in shaping its water quality. This study demonstrated that the rehabilitation works with a span of 3–4 years using herbs in riparian and/or non-riparian areas could significantly improve water quality of low-order streams with natural origin.Publication Embargo Sampling at mesoscale physical habitats to explain headwater stream water quality variations: Its comparison to equal-spaced sampling under seasonal and rainfall aided flushing …(Elsevier, 2014-11-27) Gomes, P. I. A; Wai, O. W. HWe investigated the applicability of sampling at mesoscale physical habitats (MPH) for water quality variation of headwater streams. Sampling was carried out for several hydro-environmental and water quality variables in a headwater stream subjected to moderate levels of anthropogenic disturbances. To compare results with the much popular conventional methods, sampling was also carried out at equal size stream sections (cell-in-series (CIS)). Data collection covered dry (low discharge) and wet (high discharge) seasons. Each season sampling was repeated for typical and flushed (less polluted) states of the stream. Relationships were evidenced primarily by redundancy analysis. Correlations between hydro-environmental and water quality variables were practically same for both approaches. Also, ordination diagrams showed a tendency of first order tributaries to separate from other samples or to form clusters. This was more obvious for the MPH approach. The ordination lengths between adjacent sampling locations in flushed states were much closer than the corresponding typical state for both approaches. The most influential (i.e., with the ability to explain high variance and/or significance) hydro-environmental variables varied on the approach. Habitat (sampling unit) dimensions (width and depth) had high influence in MPH approach; it was the substrate condition (fine particle fraction) for CIS approach. The total variance explained (i.e., explanatory power) by the respective approach seemed to depend on season and state. MPH approach showed highest explanatory power in dry season’s flushed state (53%) which is greater than the CIS approach. Explanatory powers of CIS approach observed to be about 50% or more for all cases, with the exception being the flushed state in dry season (36%). This study revealed some important empirical and theoretical frameworks for MPH based assessments. Firstly, MPHs are more complementary to low flows and less polluted streams. Low flow makes MPHs assimilation and attenuation optimal, making them hotspots for water quality studies. More complementary to less polluted waters elucidate that there is a capacity a MPH can work effectively on pollutant removal. Secondly, the correlation between levels of pollution expressed as a flushing signature and sampling approach elucidate that the explanatory powers of MPH and CIS approaches could be used to differentiate polluted streams against pristine or unpolluted streams. Nevertheless, these empirical and theoretical frameworks proposed need further validation. Therefore, we recommend carrying out similar studies in different geo-environmental conditions with more replications under natural as well as controlled experimental setups.