Faculty of Engineering

Permanent URI for this communityhttps://rda.sliit.lk/handle/123456789/4203

Browse

Filters

2012 - 201922020 - 20233

Advanced Search

Filter by

Settings

Author: search.filters.author.Gomes, P. I. ASubject: search.filters.subject.water quality

Search Results

Now showing 1 - 5 of 5
  • Thumbnail Image
    PublicationEmbargo
    Investigation of long-term river water quality variations using different urbanization indices and assessment of common scientific perspectives of urbanization on water quality
    (wiley, 2023-03) Karunatilaka, P. D.; Gomes, P. I. A
    This study investigated the water quality variation spanning 30 years (1986–2017) in 16 catchments of Hong Kong against different urbanization indices, namely, built area fraction; population; and product of population and built area fraction. Pearson correlations of three different periods of time (1988–1990, 1998–2000, and 2015–2017) indicated that water quality trends were dependent on the urbanization index. Total solids, nitrite-nitrogen, total phosphorus, electrical conductivity, dissolved oxygen, and flow rate had significant deteriorative trends (Pearson r > 0.5 and p < 0.05) with population and product of built area and population. Results also interpreted that built area fraction and product of built area and population were the worst and best indices that represented urbanization and/or its impacts, respectively. Mann-Kendall test for the entire 30 year period showed that water quality had improved with time with respect to certain water quality parameters (e.g., dissolved oxygen, ammoniacal nitrogen and total suspended solids). The results portrayed that although the urbanization of catchments had increased with time, the river water quality with respect to many parameters showed signs of improvement and the legislative measures implemented seemed to be effective in controlling pollution.
  • Thumbnail Image
    PublicationOpen 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. H
    Although 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”.
  • Thumbnail Image
    PublicationEmbargo
    Do sediments of ephemeral and perennial streams show different impacts on water quality when subjected to the same drying conditions?
    (Wiley Online Library, 2021) Gomes, P. I. A; Perera, M. D. D
    Empirical evidence was studied to investigate whether ephemeral stream sediments have redeeming biological and physical attributes with respect to water quality, via a laboratory mesocosm study simulating stagnant pooled conditions in ephemeral and perennial streams. In addition to stream type, the effect of sediment quantity variation (sediment to water ratio) was also studied. From the water quality parameters tested (electrical conductivity, dissolved oxygen, pH, nitrogen species and phosphate), only electrical conductivity showed a significant difference between the two stream types irrespective of sediment to water ratio. However, the temporal water quality of a given stream type changed with sediment quantity in the mesocosm. Re-flooding of mesocosms after complete drying did not result in blackwater conditions, but a similar spike in nutrient concentration was observed in both stream types. The absence of blackwater was attributed to the lack of addition of new organic matter and litter, as well as the saturation of dissolved oxygen in mesocosms, therefore, indicating that aeration and litter control could be used as mitigation methods for blackwater events. It was evident that water quality variations in ephemeral streams are purely based on the flow regime (hydrological flow conditions) and organic loading. No evidence was found for any unique biological and physical properties of ephemeral sediment that redeem water quality.
  • Thumbnail Image
    PublicationEmbargo
    Impact of increased instream heterogeneity by deflectors on the removal of hydrogen sulfide of regulated urban waterways—A laboratory study
    (Wiley Online Library, 2021-03) Gomes, P. I. A; Samararatne, S.; Wai, O. W. H; Perera, M. D. D
    Laboratory experiments were conducted to test the hypothesis that increase in physical heterogeneity by deflectors would improve the water quality of urban regulated (straight and prismatic) waterways. Deflectors changed the near-uniform flow to a rapidly var-ied flow, as such the depth, velocity, and Froude number (Fr) variations were four, 10, and 14 times more than the without deflector scenario, respectively. Removal of hydro-gen sulfide (H2S), the main focus of the study, was significantly high when deflectors were placed in the laboratory urban waterway. Introduction of a sediment bed further improved H2S removal; however, in this case turbidity and color were significantly high too. These observations endorse the fact that attenuation induced by deflectors and assimilation promoted by the sediment bed aids the H2S removal. These facts were fur-ther strengthened by the significant strong negative correlations H2S made with DO and pH for all experiments. Further studies are recommended for different deflector orientations and modified sediment beds (e.g., mixture of sediment and gravel), identi-fication of localized water quality hot spots to capture spatial variation of water quality, and impact of increased heterogeneity on flood safety
  • Thumbnail Image
    PublicationEmbargo
    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. H
    Implications 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.