Evaluation of Future Streamflow in the Upper Part of the Nilwala River Basin (Sri Lanka) under Climate Change

Climate change is a serious and complex crisis that impacts humankind in different ways. It affects the availability of water resources, especially in the tropical regions of South Asia to a greater extent. However, the impact of climate change on water resources in Sri Lanka has been the least explored. Noteworthy, this is the first study in Sri Lanka that attempts to evaluate the impact of climate change in streamflow in a watershed located in the southern coastal belt of the island. The objective of this paper is to evaluate the climate change impact on streamflow of the Upper Nilwala River Basin (UNRB), Sri Lanka. In this study, the bias-corrected rainfall data from three Regional Climate Models (RCMs) under two Representative Concentration Pathways (RCPs): RCP4.5 and RCP8.5 were fed into the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) model to obtain future streamflow. Bias correction of future rainfall data in the Nilwala River Basin (NRB) was conducted using the Linear Scaling Method (LSM). Future precipitation was projected under three timelines: 2020s (2021–2047), 2050s (2048–2073), and 2080s (2074–2099) and was compared against the baseline period from 1980 to 2020. The ensemble mean annual precipitation in the NRB is expected to rise by 3.63%, 16.49%, and 12.82% under the RCP 4.5 emission scenario during the 2020s, 2050s, and 2080s, and 4.26%, 8.94%, and 18.04% under RCP 8.5 emission scenario during 2020s, 2050s and 2080s, respectively. The future annual streamflow of the UNRB is projected to increase by 59.30% and 65.79% under the ensemble RCP4.5 and RCP8.5 climate scenarios, respectively, when compared to the baseline scenario. In addition, the seasonal flows are also expected to increase for both RCPs for all seasons with an exception during the southwest monsoon season in the 2015–2042 period under the RCP4.5 emission scenario. In general, the results of the present study demonstrate that climate and streamflow of the NRB are expected to experience changes when compared to current climatic conditions. The results of the present study will be of major importance for river basin planners and government agencies to develop sustainable water management strategies and adaptation options to offset the negative impacts of future changes in climate.publishedVersio

Comparing Combined 1D/2D and 2D Hydraulic Simulations Using High-Resolution Topographic Data: Examples from Sri Lanka—Lower Kelani River Basin

The application of numerical models to understand the behavioural pattern of a flood is widely found in the literature. However, the selection of an appropriate hydraulic model is highly essential to conduct reliable predictions. Predicting flood discharges and inundation extents are the two most important outcomes of flood simulations to stakeholders. Precise topographical data and channel geometries along a suitable hydraulic model are required to accurately predict floods. One-dimensional (1D) hydraulic models are now replaced by two-dimensional (2D) or combined 1D/2D models for higher performances. The Hydraulic Engineering Centre’s River Analysis System (HEC-RAS) has been widely used in all three forms for predicting flood characteristics. However, comparison studies among the 1D, 2D to 1D/2D models are limited in the literature to identify the better/best approach. Therefore, this research was carried out to identify the better approach using an example case study of the Kelani River basin in Sri Lanka. Two flood events (in 2016 and 2018) were separately simulated and tested for their accuracy using observed inundations and satellite-based inundations. It was found that the combined 1D/2D HEC-RAS hydraulic model outperforms other models for the prediction of flows and inundation for both flood events. Therefore, the combined model can be concluded as the better hydraulic model to predict flood characteristics of the Kelani River basin in Sri Lanka. With more flood studies, the conclusions can be more generalized.Comparing Combined 1D/2D and 2D Hydraulic Simulations Using High-Resolution Topographic Data: Examples from Sri Lanka—Lower Kelani River BasinpublishedVersio

Modelling Capabilities of Two Physically Based Hydrologic Models for Streamflow Simulations

Abstract Hydrologic processes in a watershed are typically simulated through hydrologic models due to their availability in the public domain and improved computational capacities. However, choosing a suitable model among the many available for a region of interest is challenging. In our work, we compared streamflow generated by the Soil and Water Assessment Tool (SWAT) and the Hydrological Engineering Centre-Hydrologic Modeling System (HEC-HMS) in the Kalu River Basin (KRB), Sri Lanka, frequently impacted by floods. Meteorological data including rainfall and temperature from 1990 to 2000 were used to force the hydrologic models. In addition, we used soil, land use data and a digital elevation model (DEM) for model development. During the calibration phase (1993-1996) of the SWAT model we achieved a coefficient of determination (R²) of 0.93 and a Nash-Sutcliffe Efficiency (NSE) of 0.87. In the validation phase (1997–2000), these indices yielded values of 0.87 and 0.66, respectively. In the HEC-HMS model, during the calibration phase, R2 and NSE yielded values of 0.89 and 0.91 while in the validation phase, these indices yielded values of 0.77 and 0.56, respectively. The exceedance probabilities at 10%, 50%, and 90% derived from flow duration curves (FDCs) from HEC-HMS and SWAT models were 395, 159, 54.5 and 400.5, 148, 29.11 (all in m3/s), respectively. Similarly, for observed flow, these values were 344.40, 138.98, and 65.35 m3/s, respectively. Thus, the FDCs suggest that the HEC-HMS model captures low flows reasonably. Neither model accurately resembled high flows. During the first inter-monsoon season (March-April) the HEC-HMS and SWAT underpredicted 3%, and 4% while during the northeast monsoon season (December-February) the models underpredicted 9%, and 2%, respectively. Similarly, during the second inter-monsoon season (October-November) and the southwest monsoon season (May-September), HECHMS and SWAT models overestimated observed flow by 11%, 5%, and 8%, 17%, respectively. Both models performed reasonably well on a seasonal basis with slight over-predictions and under-predictions. Overall, it is clear that both models can generally capture the hydrology of the KRB.Abstract Hydrologic processes in a watershed are typically simulated through hydrologic models due to their availability in the public domain and improved computational capacities. However, choosing a suitable model among the many available for a region of interest is challenging. In our work, we compared streamflow generated by the Soil and Water Assessment Tool (SWAT) and the Hydrological Engineering Centre-Hydrologic Modeling System (HEC-HMS) in the Kalu River Basin (KRB), Sri Lanka, frequently impacted by floods. Meteorological data including rainfall and temperature from 1990 to 2000 were used to force the hydrologic models. In addition, we used soil, land use data and a digital elevation model (DEM) for model development. During the calibration phase (1993-1996) of the SWAT model we achieved a coefficient of determination (R²) of 0.93 and a Nash-Sutcliffe Efficiency (NSE) of 0.87. In the validation phase (1997–2000), these indices yielded values of 0.87 and 0.66, respectively. In the HEC-HMS model, during the calibration phase, R2 and NSE yielded values of 0.89 and 0.91 while in the validation phase, these indices yielded values of 0.77 and 0.56, respectively. The exceedance probabilities at 10%, 50%, and 90% derived from flow duration curves (FDCs) from HEC-HMS and SWAT models were 395, 159, 54.5 and 400.5, 148, 29.11 (all in m3/s), respectively. Similarly, for observed flow, these values were 344.40, 138.98, and 65.35 m3/s, respectively. Thus, the FDCs suggest that the HEC-HMS model captures low flows reasonably. Neither model accurately resembled high flows. During the first inter-monsoon season (March-April) the HEC-HMS and SWAT underpredicted 3%, and 4% while during the northeast monsoon season (December-February) the models underpredicted 9%, and 2%, respectively. Similarly, during the second inter-monsoon season (October-November) and the southwest monsoon season (May-September), HECHMS and SWAT models overestimated observed flow by 11%, 5%, and 8%, 17%, respectively. Both models performed reasonably well on a seasonal basis with slight over-predictions and under-predictions. Overall, it is clear that both models can generally capture the hydrology of the KRB

Reusable rainwater quality at Ikorodu area of Lagos, Nigeria: Impact of first-flush and household treatment techniques

YesWater scarcity is a huge problem in Africa, and hence rainwater becomes a crucial water source for fulfilling basic human needs. However, less attention has been given by African countries to the effectiveness of common rainwater treatments to ensure the population's health. This study investigates the impact of different household treatment techniques (HHTTs), i.e. treatments by chlorine, boiling, alum, and a combination of alum and chlorine, on its storage system using a case study at the Ikorodu area of Lagos state, which is a rural area in Nigeria. The first-flush quality has been particularly studied here, where the microbial reduction through its practice has been examined from five different roofs. One of the investigated roofs was from a residential building, and four were constructed for the purpose of this study. In this study, the physical parameters (i.e. total suspended solids and turbidity) and the microbial parameters (i.e. total coliform and Escherichia coli) of the collected rainwater have been investigated. From the results, it has been observed that: (1) the water quality at the free phase zone is better than that at the tank's bottom; (2) the combination of chlorine and alum gives the best rainwater quality after comparing the application of different HHTTs; and (3) a reduction of about 40% from the original contaminant load occurs in every 1 mm diversion.Hidden Histories of Environmental Science Grant Project (at Seed-grant Stage), funded by the Natural Environment Research Council (NERC) and Arts and Humanities Research Council (AHRC), part of UK Research and Innovation (UKRI

Effects of wastewater type on stability and operating conditions control strategy in relation to the formation of aerobic granular sludge – a review

Currently, research trends on aerobic granular sludge (AGS) have integrated the operating conditions of extracellular polymeric substances (EPS) towards the stability of AGS systems in various types of wastewater with different physical and biochemical characteristics. More attention is given to the stability of the AGS system for real site applications. Although recent studies have reported comprehensively the mechanism of AGS formation and stability in relation to other intermolecular interactions such as microbial distribution, shock loading and toxicity, standard operating condition control strategies for different types of wastewater have not yet been discussed. Thus, the dimensional multi-layer structural model of AGS is discussed comprehensively in the first part of this review paper, focusing on diameter size, thickness variability of each layer and diffusion factor. This can assist in facilitating the interrelation between disposition and stability of AGS structure to correspond to the changes in wastewater types, which is the main objective and novelty of this review

Modelling Capabilities of Two Physically Based Hydrologic Models for Streamflow Simulations

Hydrologic processes in a watershed are typically simulated through hydrologic models due to their availability in the public domain and improved computational capacities. However, choosing a suitable model among the many available for a region of interest is challenging. In our work, we compared streamflow generated by the Soil and Water Assessment Tool (SWAT) and the Hydrological Engineering Centre-Hydrologic Modeling System (HEC-HMS) in the Kalu River Basin (KRB), Sri Lanka, frequently impacted by floods. Meteorological data including rainfall and temperature from 1990 to 2000 were used to force the hydrologic models. In addition, we used soil, land use data and a digital elevation model (DEM) for model development. During the calibration phase (1993-1996) of the SWAT model we achieved a coefficient of determination (R²) of 0.93 and a Nash-Sutcliffe Efficiency (NSE) of 0.87. In the validation phase (1997–2000), these indices yielded values of 0.87 and 0.66, respectively. In the HEC-HMS model, during the calibration phase, R2 and NSE yielded values of 0.89 and 0.91 while in the validation phase, these indices yielded values of 0.77 and 0.56, respectively. The exceedance probabilities at 10%, 50%, and 90% derived from flow duration curves (FDCs) from HEC-HMS and SWAT models were 395, 159, 54.5 and 400.5, 148, 29.11 (all in m3/s), respectively. Similarly, for observed flow, these values were 344.40, 138.98, and 65.35 m3/s, respectively. Thus, the FDCs suggest that the HEC-HMS model captures low flows reasonably. Neither model accurately resembled high flows. During the first inter-monsoon season (March-April) the HEC-HMS and SWAT underpredicted 3%, and 4% while during the northeast monsoon season (December-February) the models underpredicted 9%, and 2%, respectively. Similarly, during the second inter-monsoon season (October-November) and the southwest monsoon season (May-September), HECHMS and SWAT models overestimated observed flow by 11%, 5%, and 8%, 17%, respectively. Both models performed reasonably well on a seasonal basis with slight over-predictions and under-predictions. Overall, it is clear that both models can generally capture the hydrology of the KRB