Browsing by Author "Munasinghe, D.S.N."

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Benthic macro-invertebrates as environmental flow indicators – a case study: Gurugoda oya, Sri Lanka
(Sri Lanka Association for the Advancement of Science, 2014) Munasinghe, D.S.N.; Najim, M.M.M.
Environmental Flow Variation due to Mini-Hydro Diversion at Gurugoda Oya, Sri Lanka
(Department of Zoology, University of Kelaniya, Kelaniya, Sri Lanka, 2014-06) Munasinghe, D.S.N.; Najim, M.M.M.
Quantification of amounts of flows that could be diverted maintaining desired ecosystem conditions is difficult, and thus, water allocation among sectors including the environment, has emerged a growing concern in Sri Lanka. Therefore, this research focused on quantifying optimum flows that has to be maintained below the weir site of a mini-hydro power plant located at Morontota, Sri Lanka through Environmental Flow Assessment and to predict whether the flows of the Hungampola South/Morontota village section of Gurugoda Oya would be sufficient to sustain riverine biodiversity. The HEC-HMS 3.5 model was calibrated and validated for the Holombuwa catchment of the Gurugoda Oya basin. The GIS layers that were needed as input data for flow simulation were prepared using Arc GIS 10.0 and the calibrated and validated model was applied to the Alapalawela sub catchment located within the Holombuwa catchment, to generate flows for the past twenty three years (1991-2013). Simulated stream flows were characterized using thirty two different hydrological parameters. The Range of Variability Approach (RVA) targets to be maintained below the weir site were calculated using flows before hydropower diversions, and the rate of non-attainment of flows were determined for past scenarios (2011-2013). According to the RVA, Environmental Flow is not maintained at present in Gurugoda Oya below the weir. Mean rate of non-attainment of the flow of Gurugoda Oya after mini hydropower diversion is around 45% suggesting moderate level of hydrologic alteration due to impoundment. Rate of non-attainment of the indicators of hydrological alterations (IHA) group 1 parameters are in between 33% - 100%. Except for the magnitude and duration of rate of non-attainment of means of 90 day minima and all maxima values which attain a steady 0%, all other group 2 parameters vary between 33% - 67%. In the IHA group 3, timing of lower limit of annual extreme water condition could not be calculated because flow of Gurugoda Oya assumes the same minimal flow for several days, showing more than one annual minima. Annual maxima show a rate of nonattainment of 33%. Rate of non-attainment of the IHA group 4 and 5 both vary between 0% - 100%. Therefore, Hydropower diversions from Gurugoda Oya that deals with damming of the stream needs extensive analysis of environmental impacts due to changes in flow regimes. The RVA targets defined by this study could be of significance for ecosystem management and restorations plans, and could provide ecological operations for the weir.
Impacts of streamflow alteration on benthic macroinvertebrates by mini‐hydro diversion in Sri Lanka
(mini‐hydro diversion in Sri Lanka, 2021) Munasinghe, D.S.N.; Najim, M.M.M.; Quadroni, S.; Musthafa, M.M.
Our study focused on quantifying the alterations of streamfow at a weir site due to the construction of a mini-hydropower plant in the Gurugoda Oya (Sri Lanka), and evaluating the spatial responses of benthic macroinvertebrates to altered fow regime. The HEC–HMS 3.5 model was applied to the Gurugoda Oya sub-catchment to generate streamfows for the time period 1991–2013. Pre weir fows were compared to post-weir fows with 32 Indicators of Hydrologic Alteration using the range of variability approach (RVA). Concurrently, six study sites were established upstream and downstream of the weir, and benthic macroinvertebrates were sampled monthly from May to November 2013 (during the wet season). The key water physico-chemical parameters were also determined. RVA analysis showed that environmental fow was not maintained below the weir. The mean rate of non-attainment was ~ 45% suggesting a moderate level of hydrologic alteration. Benthic macroinvertebrate communities signifcantly difered between the study sites located above and below the weir, with a richness reduction due to water diversion. The spatial distribution of zoobenthic fauna was governed by water depth, dissolved oxygen content and volume fow rate. Our work provides frst evidence on the efects of small hydropower on river ecosystem in a largely understudied region. Studies like this are important to setting-up adequate e-fows.
Trend analysis of annual temperature of Colombo – a case study to assess climate change in the commercial capital of Sri Lanka
(Department of Zoology and Environmental Management, University of Kelaniya, 2015) Moragoda, M.K.N.P.; Munasinghe, D.S.N.