Hartini Kasmin

Towards a generic rainfall-runoff model for green roofs.

A simple conceptual model for green roof hydrological processes is shown to reproduce monitored data, both during a storm event, and over a longer continuous simulation period. The model comprises a substrate moisture storage component and a transient storage component. Storage within the substrate represents the roofs overall stormwater retention capacity (or initial losses). Following a storm event the retention capacity is restored by evapotranspiration (ET). However, standard methods for quantifying ET do not exist. Monthly ET values are identified using four different approaches: analysis of storm event antecedent dry weather period and initial losses data; calibration of the ET parameter in a continuous simulation model; use of the Thornthwaite ET formula; and direct laboratory measurement of evaporation. There appears to be potential to adapt the Thornthwaite ET formula to provide monthly ET estimates from local temperature data. The development of a standardized laboratory test for ET will enable differences resulting from substrate characteristics to be quantified.

Soil-roots Strength Performance of Extensive Green Roof by Using Axonopus Compressus

Green roof technology has been proven to provide potential environmental benefits including improved building thermal performance, removal of air pollution and reduced storm water runoff. Installation of green roof also involved soil element usage as a plant growth medium which creates several interactions between both strands. This study was carried out to investigate the soil-roots strength performance of green roof at different construction period up to 4 months. Axonopus compressus (pearl grass) was planted in a ExE test plot with a designated suitable soil medium. Direct shear test was conducted for each plot to determine the soil shear strength according to different construction period. In addition, some basic geotechnical testing also been carried out. The results showed that the shear strength of soil sample increased over different construction period of 1st, 2nd, 3rd and 4th month with average result 3.81 kPa, 5.55 kPa, 6.05 kPa and 6.48 kPa respectively. Shear strength of rooted soil samples was higher than the soil samples without roots (control sample). In conclusion, increment of soil-roots shear strength was due to root growth over the time. The soil-roots shear strength development of Axonopus compressus can be expressed in a linear equation as: y = 0.851x + 3.345, where y = shear stress and x = time.

Preliminary Overview on Thermal Performance of Green Roof

Green roof has shown potential contribution on improving the functional performance of buildings by lowering the roof exterior surface temperature, which is indirectly, could potentially reduce the energy demand. In addition, it is likely to provide important ecological services to urban areas through lowering of urban heat island (UHI) temperatures, increasing storm water retention and improves the biodiversity. This paper will then present the initial outcomes of the joint initiative between Malaysia Agricultural Research and Development (MARDI) and Universiti Tun Hussein Onn Malaysia (UTHM) in promoting this green technology in Malaysia. As green roof technology is still emerging, there is limited technical data available at present in Malaysian climate. The study aims to provide initial observation on the thermal performance of green roof and its effect towards surrounding and associated significant environmental benefit. In order to achieve the goal, the thermal performance of green roof system in experimental plot at MARDI had been monitored. The green roof experimental plot has been set up on two flat roofs in Horticulture Research Centre, MARDI, Serdang, Selangor and the treatments consists of two green roof system known as conventional system and self-watering system. The substrate depths were 50 mm and 100 mm. In addition, some observation on the attracted wildlife to the green roof was initiated. Based on the initial results, it is interesting to report that the temperature reduction for the green roofs on Roof 1 and Roof 2 were in averages of 6.1°C and 10°C, respectively. In conclusion, this joint study between UTHM and MARDI may facilitate the development of roof top gardening system in greening the urban area. With more studies, it will possibly highlight the engineering significance, furthermore promoting the application of green roof technology in Malaysia.

Green roof as a potential Sustainable structure for runoff reduction

Urbanisation has changed the vegetated pervious areas into impervious urban roof areas and increase water production and urban heat island effects. In attempt to solve excessive water problems in urban area, green roof or vegetated roof structure as a part of Sustainable Urban Drainage System (SUDS) structure; has been introduced to replicate the pervious vegetated area on vacant urban roofs with role to control water quantity at source. This study examined the potential of green roof at retaining rainfall with less storage available than its maximum water capacity based on the antecedent dry weather period (ADWP) of less than 24 hours. The soil composition has permeability of 0.00011 cm/s with porosity of 55.1% that is equivalent to 44.1 mm available maximum storage from its total substrate depth of 80 mm. Result shows that events with ADWP more than 19 hours were 100% retained while events with ADWP less than 15 hours has shown various retention from 50-100% retention depends on total rainfall. Therefore this study has shown that one of the main factors that affected the retention percentage was the available storage within the green roof itself due to loss activities during dry days.

The Potential of Recycled Locally-Sourced Waste Materials for Green Roof Soil Mixtures

The increase in surface runoff has become a serious environmental problem and concern in Malaysia. Hence, promoting the use of green roofs in urban areas will potentially allow some storage area and time attenuation for any rainfall. Initial studies on a few substrate mixtures were done in order to find out the properties of green roof media. These included vermiculite (V), perlite (P) and peat moss (PM) together with locally-sourced waste materials such as empty fruit bunches (EFB) and wet diaper gel (D) which are expected to potentially retain more storm water runoff. A test on the substrate mixture properties and evaporation tests were conducted on seven types of soil mixtures. The results show that a basic substrate mixture of PVPM3,5,2 has a maximum water capacity of 50%. The modification and addition of diaper gel in DVPM1,3,2 and empty fruit bunch (EFB) in PEFBPM1,0.3,2 show an increment in both mixtures’ water holding capacity (54%). All the proposed mixtures have shown permeability values larger than 0.0005 cm/s. To investigate the maximum water storage availability, the evaporation tests show that both mixtures could provide 60 - 62 mm of water storage after 34 days without rainfall under ambient climatic condition (32 ̊ to 34 ̊) whereas under extreme heat temperatures (50 ̊), both mixtures took only 1 day to provide the same storage as the ambient condition. Therefore, this study has provided an initial understanding of the properties of the substrate mixture as well as the evaporation rate of the materials tested. This information can be used to demonstrate the relationship between soil characteristics and local climatic factors (temperature).

Geophysical and Hydrochemical Characteristics of Groundwater at Kerian Irrigation Scheme

.A study was conducted to determine the potential of groundwater uses at the Kerian irrigation scheme, specifically the Selinsing irrigation area. Resistivity image profiling method was employed at four sampling locations within the study area to identify the depth and variation of aquifer layer and the possibility of hard layer presence. Investigations conducted revealed that the thickness of aquifer within the study area varies between 5 m and 10 m, which is located at a depth of 30 m to 70 m below the ground surface. The thickness of clay layer is between 1 m and 80 m which dominates the upper subsurface layer. Seven samples of groundwater were used in determining their hydrochemical and physicochemical characteristics, ionic composition, and the quality suitability for irrigation use. A preliminary characterisation based on the piper diagram provides the hydrofacies classification while Stiff diagram is used to exhibit the ionic relationship. The degree of correlation between cations and anions has been estimated in order to assess their mutual relationships. Strong positive correlation exists for Ca2+-Mg2+, Ca2+-Na+, Na+-Mg2+, Na+-K+, Ca2+-K+, Mg2+-K+, Mg2+-Cl-, K+-HCO3 -, and Na+-Cl-. Profusion of elements also reflects the composition of aquifer and the climatic conditions, which possibly contribute to the genetic relationship.