Ming Fai Chow

Evaluation of green roof performances for urban stormwater quantity and quality controls

ABSTRACT Rapid urbanization in the recent decades has quickly fuelled up the process of global warming. Many mitigation measures have been formulated and implemented in order to tackle the effect of global warming. Green roofs (roof with vegetated cover) have been proposed and implemented by various countries as one of the new environmentally friendly innovation. This paper evaluates the qualitative and quantitative performances of an extensive green roof system under tropical climate. Simulations showed that the peak discharge of stormwater run-off was reduced up to 26% in relation to concrete tile roof. Its reduction ability was decreased for storms with intense rainfall. Increment of pH was observed for the green roof run-off, and the run-off quality ranged between class I and II under Malaysia National Water Quality Index (WQI). High concentrations of phosphate were observed in the run-off samples, which showed that substrates (fertilized planting soil) might be the potential contributor. Findings indicated that there was a reduction up to around 5% for indoor temperature of the building after installation of the extensive green roof system.

Urban Stormwater Management Model and Tools for Designing Stormwater Management of Green Infrastructure Practices

Urbanization is growing rapidly in Malaysia. Rapid urbanization has known to have several negative impacts towards hydrological cycle due to decreasing of pervious area and deterioration of water quality in stormwater runoff. One of the negative impacts of urbanization is the congestion of the stormwater drainage system and this situation leading to flash flood problem and water quality degradation. There are many urban stormwater management softwares available in the market such as Storm Water Drainage System design and analysis program (DRAINS), Urban Drainage and Sewer Model (MOUSE), InfoWorks River Simulation (InfoWork RS), Hydrological Simulation Program-Fortran (HSPF), Distributed Routing Rainfall-Runoff Model (DR3M), Storm Water Management Model (SWMM), XP Storm Water Management Model (XPSWMM), MIKE-SWMM, Quality-Quantity Simulators (QQS), Storage, Treatment, Overflow, Runoff Model (STORM), and Hydrologic Engineering Centre-Hydrologic Modelling System (HEC-HMS). In this paper, we are going to discuss briefly about several softwares and their functionality, accessibility, characteristics and components in the quantity analysis of the hydrological design software and compare it with MSMA Design Aid and Database. Green Infrastructure (GI) is one of the main topics that has widely been discussed all over the world. Every development in the urban area is related to GI. GI can be defined as green area build in the develop area such as forest, park, wetland or floodway. The role of GI is to improve life standard such as water filtration or flood control. Among the twenty models that have been compared to MSMA SME, ten models were selected to conduct a comprehensive review for this study. These are known to be widely accepted by water resource researchers. These ten tools are further classified into three major categories as models that address the stormwater management ability of GI in terms of quantity and quality, models that have the capability of conducting the economic analysis of GI and models that can address both stormwater management and economic aspects together.

Evaluation of stormwater runoff quality during monsoon and inter-monsoon seasons at tropical urban catchments

ABSTRACT Information on pollution level and the influence of a hydrologic regime on stormwater pollutant loading in tropical urban areas remains scarce. More local data is still required, as rainfall and runoff generation processes in tropical environment differ greatly from temperate regions. This study compares the stormwater runoff quality from urban catchments during monsoon and inter-monsoon seasons in the south of Peninsular Malaysia. Stormwater samples and flow rate data were collected from 38 storm events at three individual sites. Samples were analysed for total suspended solids (TSS), 5-day biochemical oxygen demand (BOD), chemical oxygen demand (COD), oil and grease (O&G), nitrate nitrogen (NO3-N), ammoniacal nitrogen (NH3-N), and total phosphorus (TP). Event mean concentration (EMC) was calculated for each pollutant for every monitored storm event at all study sites. The Mann–Whitney test was used to test for significance (p < 5%) in differences between the median EMCs of the pollutants. The results revealed that EMCs for stormwater runoff during the monsoon season were lower than that during the inter-monsoon season. Significant differences (p < .05) were found for EMC values for TSS, oil and grease, NH3-N, and TP but not for BOD, COD, and NO3-N. Stormwater pollutant loading of TSS, NH3-N, and TP is higher during the inter-monsoon season while BOD, COD, and NO3-N show higher loadings during the monsoon season. A better understanding of pollutant transport mechanisms will aid in formulating an effective stormwater management measures to control the urban stormwater pollution in the tropics.

Effects of slopes on the stormwater attenuation performance in extensive green roof

This study is aimed to determine the effects of slope on stormwater retention and peak flow attenuation performances in extensive green roof in Malaysia. One green roof test bed with dimensions of 2.0 m (length) x 1 m (width) x 0.2 m (height) was constructed in Universiti Tenaga Nasional. The substrate layer was fixed as 130 mm depth and placed on top of the filter fabric and drainage layers. The green roof test bed was planted with Portulaca Grandiflora (sedum species) as the native plant in Malaysia. Different slopes (0 o, 2 o, 5 o and 7 o) of green roof test bed were tested in this study for its stormwater retention and peak flow attenuation performances. The results show that stormwater retention percentages are ranged from 56.9% to 52.3%. The stormwater retention percentages are decreased as slope increased in this study. Flat slope showed the longest observed time of peak flow while the 7 o slope has the shortest observed time of peak flow. This finding suggests that slope has a significant impact to the stormwater retention and peak flow attenuation performances in extensive green roof.

Environmental Benefits of Green Roof to the Sustainable Urban Development: A Review

With rapid growth of population and the increasing demands for higher living standards, the development of urban infrastructures and buildings are likely to increase the impervious surfaces in the river basin. Green roofs have a famous strategy in the sustainable urban development strategies in recent decades. Green roof is a viable means of increasing the amount of vegetation in urban cities, where the open space at ground level is limited but roof tops are largely unused yet remain impervious and contribute to storm water runoff. This paper is aimed to review comprehensively the types, components, and environmental benefits of green roofs to the sustainable urban development. Generally, green roofs provide a lot of advantages for example decreasing consumption of energy by reducing heating and cooling loads, increase building standards, provide aesthetic value and amenity, improves urban air quality, increase storm water runoff mitigation, decrease air temperatures, decrease noise in urban environments, support in urban storm water pollutant removal, and mitigate urban heat island effects. This paper also reviewed the development and application of green roofs in different countries. In conclusion, more implementation of green roofs in the urban city should be promoted in order to ensure the sustainability of the urban development.

Contributions of Dry and Wet Weather Runoffs to Annual Pollutant Loading in Tropical Urban Catchments

This study compares the relative contributions of potential contaminants discharged in dry weather flow (DWF) and wet weather flow (WWF) from typical type of catchments in Malaysia. A total of 52 storm events were monitored for WWF quality evaluation. Hourly DWF samples were also collected manually during selected weekday (Wednesday) and weekend (Saturday and Sunday). All water samples were analyzed for TSS, COD, BOD, oil and grease (O&G), NO2–N, NO3–N, NH3–N, soluble P, total P and Zinc. The results indicate that TSS, BOD, COD and O&G were mostly transported in WWF than in DWF. More than 70% of the total annual load of TSS and O&G were transported in storm water runoff. Conversely, annual loadings of NH3–N and soluble P were mainly evacuated by DWF at the commercial and industrial catchments. Storm water runoff contributes greater loadings of N and P in the residential catchment. In general, each pollutant and land use would give different relative contributions to the annual pollutant loadings. In conclusion, this study have recognized the relative pollutant loading contributions by dry and wet weather flows in typical urban catchments in Malaysia. This findings will help the decision makers to develop better target specific pollutant treatment strategies to reduce the urban water pollution.

Spatial Variability of Rainfall in Urban Catchment

The rapid urbanization process has created massive pressure on the environment and interrupted the water balance. In this research, Penchala River was chosen as the research area. Spatial variability of rainfall can lead to significant error in rainfall–runoff processes and hydrological modeling, specifically in the urban area. Thus, one-way analysis of variance (ANOVA) was used to determine whether there are any statistically significant differences between the means of rainfall data from selected rainfall stations. The yearly and monthly data of all eight rainfall stations during the period of the year, 2012–2015 was used for this analysis. The post hoc test was used to identified, in which rainfall station differed among each other during the study. The null hypothesis (no significant difference) is accepted, when the computed p value is more than 0.05. The results showed that there is no significant statistical difference in the rainfall data between the rain gauges of S1–S8 with the p-values 0.945 (2012), 0.954 (2013), 0.342 (2014), and 0.427 (2015). It can be concluded that none of the gauge used for the determination of rainfall dataset contained systematic errors.

Identification of Vulnerable Regions for TNB’s Electric Substations during Flood in Peninsular Malaysia

Flood is usually an environmental hazard which has been increased in recent years by forcing the pushing factors such as climate change and urbanization. This study presents flood-prone area related to the electric substations for Tenaga Nasional Berhad (TNB) in Peninsular Malaysia. The objective of this research was to identify the related regions that the electric substations are in vulnerable condition by flood risk. For this research, two types of maps are generated, namely flood inundation map (FIM), which indicates the area and capacity of the flood, and flood hazard map (FHM), which provides the area, depth, velocity, and extension of the flood for the TNB’s location of substation. For this issue, different classes of substations are involved in analysis, namely transmission main intake (PMU), main distribution (PPU), main switching station (SSU), and distribution substation (PE). An integration of TNB’s substation maps performed with FIM and FHM due to identify substations which are in flood-prone regions. Generally, result shows that Kelantan is classified as the highest flood-prone region for TNB’s infrastructures especially for PMU which they are affected by flood. Kelantan, Terengganu, and Perlis are involved with the highest flooded, respectively, based on PPU and SSU infrastructure. Finally, for PE substations, Kelantan, Perlis, and Terengganu have the highest contribution for flooded substations for TNB’s structures.

Analysis of Rainfall Trend and Temporal Patterns: A Case Study for Penchala River Basin, Kuala Lumpur

Changing of rainfall pattern and trend has increased the flooding risk in urban areas in the recent decades. This study aimed to examine the rainfall trends and its temporal rainfall pattern in Penchala River basin. Rainfall data of 5-min interval from 2005 to 2014 were obtained from Department of Irrigation and Drainage Malaysia (DID). The Mann-Kendall (MK) test was used to detect the trends of rainfall while average variability method (AVM) was used to derive the rainfall temporal pattern in the studied river basin. The historical rainfall data in Penchala River basin show a downward trend in the past 10 years, especially in February. Meanwhile, positive trends were detected in October, November, and December. Most of the rainfall events in Penchala River basin are categorized as advanced and intermediate type pattern. Higher fraction of rainfall occurs at the early part of storm event in the Penchala River basin, compared to that of Kuala Lumpur region.