Lloyd Chua

• Doctor of Philosophy
• Professor (Associate) at Deakin University

Surface water plays an important role in understanding the hydrological behaviour of a wetland and is crucial for the sustainability of wetland ecosystems. Remote sensing increasingly is used for the estimation of surface water levels in larger inland waterbodies. However, there are few investigations that have employed multi-sourced remote sensing...

Urbanization contributes to an increase in flood frequency and intensity, which is exacerbated by climate change. This is a phenomenon observed in both developing and industrialized countries, including Malaysia and Thailand. It is possible to lessen the devastation that natural catastrophes cause as a result of climate change by making timely and...

Floating wetland systems potentially can provide a diverse set of ecosystem services that collectively improve urban resilience. Despite the growing studies and use of floating wetlands in temperate and subtropical climates, the design of floating wetlands in tropical climates is still understudied. This paper therefore aims to identify the researc...

Weirs are widely used in hydraulic structures to control and regulate flow in open channels. Gabion weirs are frequently used in rivers, small dams, energy dissipaters, flood control works, and check dams, among other uses, and can be used to build a stepped weir. Dissipation of the energy (kinetic energy) on spillways or weirs is important to prot...

Weirs are hydraulic structures generally used in open channels to regulate and control flow. Gabion weirs are considered an economical alternative to use in areas where rock-fill materials are available Energy dissipation in weirs and spillways is critical as uncontrolled dissipation can cause damage to hydraulic structures and the downstream chann...

Urbanization continues to increase in countries with tropical climates and this trend, combined with the likely increasing frequency of extreme rainfall events due to a changing climate, places such development at risk and in need of resiliency assessment. Conceptual models to assess runoff dynamics can be an important component of resiliency asses...

Purpose The objective of this paper is to review nature-based solution (NbS) research and design practices and identify knowledge gaps that may create barriers to effective NbS implementation for management of particle-bound metals. Methods A case study of two constructed wetlands in residential areas of Geelong, Australia, is presented with an ex...

The application of in situ monitoring to characterize the dynamics of urban, peri-urban, and natural water environments from Southeast Asia, North America, and Australia is explored in this chapter. Focusing on water temperature, dissolved oxygen, turbidity, chlorophyll a, specific conductivity, and pH, important considerations in the deployment an...

River morphological change is the complex evolution of riverbed states, which can lead to serious riverbank failures, and is a worldwide concern. However, revealing the cause of the evolution, in particular, the potential morphological scouring by eddy currents, is difficult. Accordingly, we propose a comprehensive combination of 2D and 3D simulati...

A three-dimensional hydrodynamic-ecological lake model combined with field measurements and sampling was applied to investigate the impacts of floating photovoltaic (PV) systems on hydrodynamics and water quality in a shallow tropical reservoir in Singapore. The model was validated using field data and subsequently applied to predict temperature an...

Most of the studies on EMC (Event mean concentration) and first flush are reported as local studies; however variations of EMC and first flush across catchments in different climate zones has not been studied. This research collected continuous flow and discrete water quality data and rainfall measurements from 17 catchments, EMC and rainfall data...

The wind field over an urban lake may exhibit considerable variability resulting from wind-shielding effects from surrounding structures. Field measurements at an urban reservoir in Singapore were augmented by computational fluid dynamics (CFD) model results to develop a wind model over the reservoir surface via a data assimilation approach. The fi...

Microbial communities play a vital role in nitrogen (N) removal in constructed wetlands (CWs). However, the lack of studies on microbial characteristics of wetland systems designed to treat stormwater demonstrates the importance of comprehensive investigation on microbial response to wetland fluctuations. Moreover, the observed inconsistency in N r...

Rainfall-derived infiltration and inflow (RDII), the subsurface flow that enters a drainage system during and sometimes long after cessation of rainfall, may negatively impact system performance and cost. Accounting for RDII, however, is subject to a number of uncertainties, of which land use land cover (LULC) constitutes a major factor. One of the...

Water samples were collected from a constructed wetland in Armstrong Creek, Geelong, for eight storm events. For each sampling, a single surface sample was collected at the deepest point of five equidistant transects across the wetland in the 12, 36 and 60 h following the storm events. The samples were tested for total suspended solids (TSS), total...

Coupled with climate change, the urbanization-driven increase in the frequency and intensity of floods can be seen in both developing and developed countries, and Malaysia is no exemption. As part of flood hazard mitigation, this study aimed to simulate the urban flood scenarios in Malaysia’s urbanized catchments. The flood simulation was performed...

Shortwave radiation, longwave radiation, photovoltaic (PV) panel, air and near-surface water temperature data were measured for a floating PV system installed in a shallow tropical reservoir. Similar air and water temperature measurements were conducted in open water (ambient condition) for comparison. The data indicate that shortwave radiation is...

A combination of discrete sampling using autosamplers triggered by area-velocity meters and continuous water quality monitoring using YSI datasondes enabled us to evaluate the dynamics of both stormwater runoff and dry weather water quality associated with an urban park and WSUD treatment train in Singapore. The WSUD treatment train consisted of a...

Modeling the washoff of pollutants from urban catchments is a difficult task. Although the exponential washoff model has been in use for decades, there is a general lack of data on model parameters and much less is known about how the model parameters are influenced by storm and climate characteristics. This study was done to understand how model p...

The bioretention basin is a type of green infrastructure that treats stormwater runoff. However, there is a limited understanding of its treatment potential with different design configurations and limited capability to model bioretention systems. Current modeling practice fails to represent bacteria-mediated biochemical reactions that remove nitro...

The discharge of high levels of heavy metals into the environment is of concern due to its toxicity to aquatic life and potential human health impacts. Biofiltration systems have been used in urban environments to address nutrient contamination, but there is also evidence that such systems can be effective in reducing heavy metals concentration in...

Water Sensitive Urban Design (WSUD) features increasingly are used for urban water management, green urban design, and improved community liveability, but relatively less data are available on the ecosystem services that WSUD provides. We used hedonic pricing, supported by qualitative surveys, in Geelong, Australia and Singapore, to evaluate benefi...

The main objective of this research was to investigate the impact of the construction of Karkheh Dam in 2001 (referred to as the intervention time), on groundwater quality. The time series of total dissolved solids (TDS) and other water quality data including potassium (K⁺), sodium (Na⁺), magnesium (Mg²⁺), calcium (Ca²⁺), bicarbonate (HCO3⁻), sulfa...

Urbanization rates are increasing in developing countries such as Malaysia. In the tropics, flooding is a major concern, due to high rainfall intensities. In addition to flooding, pollution caused by contaminants contained in urban runoff are also of concern. Biofiltration system as one of the technologies in on-site stormwater treatment, has gaine...

Recent advancements in neuro-fuzzy models (NFMs) have made possible the implementation of dynamic rule base systems. This is in comparison with static applications commonly seen in global NFMs such as the Adaptive-Network-Based Fuzzy Inference System (ANFIS) model widely used in hydrological modeling. This study underlines key differences between l...

Operational hydrometric network is an essential element in hydropower reservoir operation. The data collected, to be used for reservoir management and decision making require high reliability with automatic data monitoring, processing and retrieval. However, the unique characteristic of every catchment and operational requirements raises the need t...

ABSTRACT: Using a case study approach from past projects in Thailand, Vietnam, Singapore, Cambodia, and Australia, we examine the benefits, but also some of the challenges to including green space in urban design. Green space can have multiple physical and psychological well-being benefits, as well as environmental benefits, including urban runoff...

An emerging green infrastructure, the bioretention basin, has been deployed world-wide to reduce peak flows, encourage infiltration, and treat pollutants. However, inadequate design of a basin impairs its treatment potential and necessitates the development and validation of a suitable hydrological model for design and analysis of bioretention basi...

The learning algorithms in many of conventional Neuro-Fuzzy Systems (NFS) are based on batch or global learning where all parameters of the fuzzy system are optimized off-line. Although these models have frequently been used, they suffer from a reduced flexibility in their architecture as the number of rules need to be predefined by the user. This...

Accurate prediction of pan evaporation (PE) is one of the crucial factors in water resource management and planning in agriculture. In this research, two hybrid models, self-adaptive time-frequency methodology, ensemble empirical mode decomposition (EEMD) coupled with support vector machine (EEMD-SVM) and EEMD model tree (EEMD-MT) were employed to...

Critical issues governing the performance of hydraulic structures such as spillways and chutes include stability and safety of the structure itself. The stepped spillway aims to dissipate the energy of the flow, which will decrease the stilling basin volume and the risk of cavitation. It is important to have a good understanding of flow characteris...

Rainwater harvesting (RWH) can be considered as a water source especially for remote areas in Indonesia as the country is in the tropics, and has abundant rainfall. This research was aimed at identifying the ability of RWH as a reliable water supply at the domestic level using building cost, water consumption rates and quality as indicators. We bui...

The global learning method is widely used to train data-driven models for hydrological forecasting. The drawback of global models is that a long data record is required and the model is not easily adapted once it is trained. This study investigated the local learning approach applied in the dynamic evolving neural-fuzzy inference system (DENFIS) to...

This study applied an atmospheric Computational Fluid Dynamics (CFD) model and a three-dimensional hydrodynamic-ecological lake model to investigate the impacts of variable wind forcing on lake hydrodynamics and water quality. The CFD model was used to predict the wind field over the lake surface which served as the meteorological forcing for the l...

Community-based water supply (CBWS) is an example of how a community manages common pool resources (CPR). This results in an alternative approach to solve water supply problems in developing countries by enhancing community participation in managing water supply. This research evaluates the sustainability of five CBWS projects in Cikarang, Indonesi...

The stepped spillway is a hydraulic structure, mostly used in dams. Normally, stepped spillways were designed to increase the energy dissipation level and hence decrease the risks at downstream. The current experimental investigation includes two groups of scale models, each with four different variables, to investigate the impact of step shape on...

Washoff behavior in the tropics is expected to behave differently from temperate areas due to differences in rainfall characteristics. In this study, rainfall, runoff and total suspended solids (TSS) were monitored from 9 catchments distinguished by different types of land use, in Singapore. The catchments ranged in size from 5.7ha to 85.2ha. Over...

A major challenge for assessment of water quality in tropical environments is the natural occurrence and potential growth of Fecal Indicator Bacteria (FIB). To gain a better understanding of the relationship between measured levels of FIB and the distribution of sewage-associated bacteria including potential pathogens in the tropics this study comp...

Accurate and reliable flood forecasting is essential to mitigate the threats brought by floods. Ensemble approaches have been used in limited studies to improve the forecasts of component models. In this paper an ensemble model based on neural-fuzzy inference system (NFIS) and three real time updating approaches were used to synthesize the water le...

Neuro-Fuzzy Systems (NFS) are computational intelligence tools that have recently been employed in hydrological modeling. In many of the common NFS the learning algorithms used are based on batch learning where all the parameters of the fuzzy system are optimized off-line. Although these models have frequently been used, there is a criticism on suc...

Non-point source pollution is a prevalent problem throughout the world. Bioretention basins have been deployed worldwide to treat stormwater runoff and alleviate eutrophication in downstream water resources. However, basin performance in the tropics is poorly understood. Given the distinctly different rainfall-runoff characteristics of tropical cli...

Current state-of-the-art online neuro fuzzy models (NFMs) such as DENFIS (Dynamic Evolving Neural-Fuzzy Inference System) have been used for runoff forecasting. Online NFMs adopt a local learning approach and are able to adapt to changes continuously. The DENFIS model however requires upper/lower bound for normalization and also the number of rules...

Bioretention basins or rain gardens are constructed green infrastructure in developed areas that retain and treat stormwater runoff. This study evaluates whether a tropical basin in Singapore that is built according to design guidelines from temperate countries has sufficient storage and infiltration capacity to handle tropical storms. Flow measure...

Surface water contamination by human faecal wastes is a widespread hazard for human health. Faecal indicator bacteria (FIB) are the most widely used indicators to assess surface water quality but are less-human-specific and have the potential to survive longer and/or occur naturally in tropical areas. In this study, 13 wastewater chemicals (chlorid...

Aims: The study goals were to determine the relationship between faecal indicator bacteria (FIB), the HF183 marker and land use, and the phylogenetic diversity of HF183 marker sequences in a tropical urban watershed. Methods and Results: Total coliforms, Escherichia coli, and HF183 were quantified in 81 samples categorized as undeveloped, residenti...

Human faecal contamination poses a widespread hazard for human health. In urban areas, sewer leakage may be an important cause of faecal pollution to surface water. Faecal indicator bacteria (FIB) are the most widely used indicators to monitor surface water quality. However, assessing whether a water body is meeting water quality criteria is made d...

We study the water quality in an urban district, where the surface wind distribution is an essential input but undergoes high spatial and temporal variations due to the impact of surrounding buildings. In this work, we develop an optimal sensor placement scheme to measure the wind distribution over a large urban reservoir using a limited number of...

Water quality monitoring and prediction are critical for ensuring the sustainability of water resources which are essential for social security, especially for countries with limited land like Singapore. For example, the Singapore government identified water as a new growth sector and committed in 2006 to invest S$ 330 million over the following fi...

Human faecal sources of contamination pose a hazard to human health. Faecal indicator bacteria (FIB) are the most widely used indicators to monitor faecal contamination in surface waters. However, assessing whether a water body is meeting water quality criteria is made difficult by the high variability of FIB concentrations over time. This study ai...

Urbanization has profound influence on the hydrologic response of landscapes. Urban transformation affects the storages and processes that determine the generation of hydrologic fluxes. It also changes the time-scales associated with hydrologic processes. Shifts in hydrologic response of the watershed unit due to urban transformation may be more co...

This paper presents the application of an improved particle swarm optimization (PSO) technique for training an artificial neural network (ANN) to predict water levels for the HeshuiWatershed, China. Daily values of rainfall and water levels from 1988 to 2000 were first analyzed using ANNs trained with the conjugate gradient, gradient descent, and L...

We collaborate with environmental scientists to study the hydrodynamics and water quality in an urban district, where the surface wind distribution is an essential input but undergoes high spatial and temporal variations due to the complex urban landform created by surrounding buildings. In this work, we study an optimal sensor placement scheme to...

Results from the application of adaptive neuro-fuzzy inference system (ANFIS) to forecast water levels at 3 stations along the mainstream of the Lower Mekong River are reported in this paper. The study investigated the effects of including water levels from upstream stations and tributaries, and rainfall as inputs to ANFIS models developed for the...

HF183 marker genome equivalents (GE 100 ml−1) in Kranji Reservoir and catchment samples collected in January 2009 (a) and July 2009 (b). *denotes samples with HF levels below detection (i.e. <150 GE 100 ml−1). Sample and colour codes: undeveloped area (U) (purple bars), farming/horticultural area (F) (green bars), residential area (R) (orange bars)...

Water resources in Singapore are managed following the principles of a closed loop hydrologic cycle by one agency, the Public Utility Board (PUB), which promotes its management philosophy through the Four National Taps of Singapore program. The four national taps are: water from local catchment areas; imported water (from Malaysia); reused water (k...

The study goals were to determine the relationship between fecal indicator bacteria (FIB), the HF183 marker and land-use, and the phylogenetic diversity of HF183 marker sequences in a tropical urban watershed. Total coliforms, Escherichia coli, and HF183 were quantified in 81 samples categorized as undeveloped, residential, and horticultural from t...

Urban lakes are typically smaller, shallower, and more exposed to human activities than natural lakes. Although the effects of harmful algal blooms (HABs) associated with eutrophication in urban lakes has become a growing concern for water resources management and environmental protection, studies focussing on this topic in relation to urban lakes...

Developing an efficient and accurate hydrologic forecasting model is crucial to managing water resources and flooding issues. In this study, response surface (RS) models including multiple linear regression (MLR), quadratic response surface (QRS), and nonlinear response surface (NRS) were applied to daily runoff (e.g., discharge and water level) pr...

A study using local learning Neuro-Fuzzy System (NFS) was undertaken for a rainfall-runoff modeling application. The local learning model was first tested on three different catchments: an outdoor experimental catchment measuring 25 m(2) (Catchment 1), a small urban catchment 5.6 km(2) in size (Catchment 2), and a large rural watershed with area of...

This study investigated the performance of a floating wetlands system (FWS) planted with Chrysopogon zizanioides (Vetiver grass), Typha angustifolia and Polygonum barbatum as treatment units to remove nutrients contained in the baseflow to the Kranji reservoir in Singapore. Phase 1 of the study consisted of controlled experiments with a perspex flo...

The temporal variation of local pier scour depth is very complex, especially for cases where the bed comprises a sediment mixture. Many semi-empirical models have been proposed to predict the time-dependent local pier scour depth. In this paper, an alternative approach, the support vector regression method (SVR) is used to estimate the temporal var...

Accurate water level forecasts are essential for flood warning. This study adopts a data‐driven approach based on the adaptive network–based fuzzy inference system (ANFIS) to forecast the daily water levels of the Lower Mekong River at Pakse, Lao People's Democratic Republic. ANFIS is a hybrid system combining fuzzy inference system and artificial...

In this study, flow forecasts by data driven models were compared with predictions by physically-based models for two (a 25 m 2 plane surface and a sub-watershed in the Lower Mekong Basin) catchments of contrasting sizes. The comparisons reveal that physically-based models fared worse than data driven models, due mainly to the specification of fore...

This study investigated the effect of lag time on the performance of data-driven models, specifically the adaptive network-based fuzzy inference system (ANFIS), in event-based rainfall-runoff modeling. Rainfall and runoff data for a catchment in Singapore were chosen for this study. For the purpose of this study, lag time was determined from cross-...

Mathematical models require the estimation of rainfall abstractions for accurate predictions of runoff. Although loss models such as the constant loss and exponential loss models are commonly used, these methods are based on simplified assumptions of the physical process. A new approach based on the data driven paradigm to estimate rainfall abstrac...

A fully distributed hydrological model (MOBIDIC) is applied to study the impact of urbanization on local hydrology in the Kranji watershed, Northwest Singapore. Based on the available data, the MOBIDIC is firstly calibrated at the two sub-watersheds (KC2 and KC6), where the percentages of urbanized area are 80% in KC2, while 6% in KC6. Different ur...

This paper applies dimensional analysis to propose an alternative model for estimating the effective density of flocs (Delta rho(f)). The model takes into account the effective density of the primary particles, in addition to the sizes of the floc and primary particles, and does not consider the concept of self-similarity. The model contains three...

Event-based runoff forecasting for 1, 2, 4 and 8 time steps ahead, based on rainfall and flow data of ten storm events for an asphalt plane, have been investigated by the Artificial Neural Network (ANN) technique. The investigation includes ANN models with three different types of inputs: (i) rainfall only, (ii) discharge only and (iii) a combinati...

The results of a study using linear artificial neural networks (ANNs) to determine the physical parameters in event-based rainfall–runoff modeling are presented in this paper. The input structure of the ANN was determined based on an analysis of the discretized form of the kinematic wave equations, and the physical parameters were obtained through...

Intelligent computing tools based on fuzzy logic and Artificial Neural Networks (ANN) have been successfully applied in various problems with superior performances. A new approach of combining these two powerful AI tools, known as neuro-fuzzy systems, has increasingly attracted scientists in different fields. Although many studies have been carried...

This study investigates the effect of inputs used on event-based runoff forecasting by ANFIS. Fifteen ANFIS models were compared, differentiated by the choice of rainfall and/or discharge inputs used. Inputs to the ANFIS models consisted of (i) two models consisting of n + 1 inputs of a sequential rainfall time series (Rt, Rt−1, Rt−2, … , Rt−n), (i...