Research Papers - Department of Civil Engineering
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Publication Embargo Feasibility of hydrological modelling for intermittent streams using HEC-HMS: a process evaluation(Taylor and Francis, 2025-01-08) Perera, M. D.D; Gomes, P.I.AThe use of hydrological software in simulating the rainfall–runoff relationships of intermittent streams is rather unfound due to their dynamic flow regimes. This study assessed the feasibility of using Hydrologic Engineering Center–Hydrologic Modelling System (HEC-HMS), a widely used open-source hydrological modelling software, in discharge simulation of intermittent streams in a dry tropical zone. Individual calibration was required for each stream, even in adjoining sub-catchments with the same geology and climate. Event-based models with transitional periods captured seasonal variations in catchment characteristics. Strong correlations (Pearson’s r > 0.7, P < 0.05) between observed and simulated discharges indicated model success and, after calibration for one season, flows of the next (similar) season could be predicted without further adjustments. Baseflow and channel infiltration were the most sensitive parameters in the wet and dry seasons, respectively. This study demonstrated the possibility of building accurate hydrological models for intermittent streams by incorporating seasonal variations and extensive calibration.Publication Open Access Evaluation of mesoscale physical habitats in sediment and water quality improvement – a mesocosm study for urban canals(Inderscience Publishers, 2025) De Zoysa, S; Chandeep, K. A.T; Pathirathne, P.H.D.R; Gomes, P.I.AThis study investigated the applicability of different types of attenuation processes (i.e., aeration and stirring) with and without dilution in nutrients (nitrogen and phosphorous) and sulphide-polluted sediment cleanup via laboratory mesocosms. Attenuation refers to the decline in contaminant concentration, a phenomenon driven by processes like dilution, mixing, and dispersion. Dilution, a remedial method involving the blending of contaminated water with uncontaminated often happens with uncontaminated runoff or a tributary. Regardless of the seasons, aeration, stirring, combined aeration and stirring, and dilution generally resulted in better removal efficiency of pollutants. Aeration combined with stirring showed notable improvements across multiple water quality parameters, and parameters seemed to be treatment type dependent, but without any significant differences. Dilution reduced electrical conductivity and increased dissolved oxygen but did not influence ammoniacal nitrogen and phosphate. The energy consumption for a unit percentage improvement via aeration and stirring was 0.04–0.25 USD and 0.03–0.15 USD, respectively. Therefore, relying solely on attenuation processes without dilution is deemed economically infeasible in real or prototype applications. This research sheds light on potential applications including pros and cons, emphasising the need for a balanced approach, and setting the stage for future studies.Publication Embargo Hydrodynamic adjustment of mean flow and turbulence around a sinking boulder during local scouring(Springer Science and Business Media Deutschland GmbH, 2025-04) Ye, C; Zhang, Q. Y; Wang, X. K; Lei, M; Gomes, P.I.A; Yan, X, FThe fact that on a live bed, boulders tend to sink during scouring is usually ignored, weakening the true understanding of hydrodynamics in boulder beds. In this paper, flume experiments were conducted to investigate the hydrodynamics around a boulder over a movable bed with a particle tracking velocimetry (PTV) system. By measuring the velocity field, the major flow characteristics, such as velocity distribution, turbulent kinetic energy (TKE) and bed shear stress, were analyzed. The results show that the sinking boulder apparently mediates the local flow structure and turbulence pattern. The near wake region is located in the range of 2D (D is the particle size of the boulder) downstream of the boulder. There is a near-bed countercurrent in the near wake region, the TKE increase sharply, and the velocity distribution deviates from the logarithmic distribution. Compared with the flat bed, the turbulent kinetic energy extreme point of the boulder riverbed in the near wake area deviate from the bed surface to the water depth at the top of the boulder, and the direction reversal and extreme point appear at the top of the boulder. The bed shear stress increases sharply in the near wake region of 1.5 ~ 2D.Publication Open Access A Comparative Investigation of Infiltration and Channel Roughness of Ephemeral and Perennial Streams in a Mountainous Catchment(John Wiley, 2025-06) Khaniya, B; Gomes, P.I.A; Perera,M. D.D; Wai, O, W.HInfiltration and channel roughness, two major factors that govern stream discharge, were studied in similar-sized ephemeral and perennial streams in a mountainous tropical catchment. Seasons were defined based on two ephemeral flow conditions, i.e., with (wet season) and without (dry season) surface flow. A stream was divided transversely into low-flow areas (close to the thalweg) and high-flow areas (close to the channel margin). The highest average infiltration (~50 mm/h) was observed in the low flow areas around the thalweg of ephemeral streams in the dry season and was significantly higher than for any other spatial scale or temporal period. The infiltration in high-flow areas did not show a statistically significant difference between the two stream types, and surprisingly, perennial streams in the dry season showed higher infiltration than ephemeral streams. Since sediment moisture and organic content showed negative and positive correlations with infiltration, respectively, for both stream types and ephemeral streams showed statistically significant negative correlations between litter and infiltration during the dry season, the low infiltration in ephemeral high flow areas was attributed to stream-type dependent litter processing. The litter of ephemeral stream high-flow areas was subject to partial decomposition due to rapid drying and had residue of previously buried litter. Ephemeral channels were two to three times rougher than perennial channels. Standing crop biomass and mean particle size increased stream roughness in both stream types but were less prominent in ephemeral streams due to the presence of litter. The study demonstrated that litter has a special role in defining the infiltration pattern, channel roughness, and flood control potential of ephemeral streams.Publication Embargo Classification, subsurface and surface sediment physical properties, and bank stability of non-perennial and perennial headwater streams of a tropical climate(Springer Nature Link, 2025-11-20) Gomes, P.I.A; Perera,M. D. D; Karunarathna J.M.G.L.D.Over 100 reaches of perennial streams (PS) and non-perennial streams (NPS) were classified based on the Rosgen stream classification. NPS were mainly type B (39%), characterized by moderate entrenchment and low sinuosity. The remainder were almost equally split between three different classes, highlighting the morphological diversity of NPS. Fifty-nine percent of PS belonged to type C; such streams are slightly entrenched, less sinuous and have a sequential riffle-pool configuration. Surface particles were significantly coarser than the subsurface in both stream types in thalweg and low flow areas, whereas in NPS, this was prominent, showing 4–5 times more armoring than PS. Even though the NPS had a significantly coarser surface sediment layer than PS in thalweg and low flow areas, its subsurface sediment showed similar particle sizes to PS; this is an indication of surface armoring and provision of more infiltration of fine particles in NPS. A two-year return period flow event did not result in a change of the cross-section profiles. In both stream types, the horizontal force required to uproot herbaceous vegetation with unexposed roots under moist conditions manually was higher than the tractive force at high flows; however, at bankfull flows, it was lower. Also, the uprooting force in PS was lower than that of NPS, indicating that NPS banks are more stable, and numerical analyses showed they are stable under the self-weight.