Constructed Rain Garden For Water Sensitive Urban Design (Wsud) As Stormwater Management In Malaysia: A Literature Review

Water Sensitive Urban Design (WSUD) was used as intergrated approach to manage urban stormwater which currently has become a public concern in Malaysia. As a part of WSUD, rain gardens are recommended technology for new stormwater management in Malaysia. There is no performance data for this system, specifically at the field scale in Malaysia. Rain gardens are a part of Water Sensitive Urban Drainage (WSUD) in approach to urban planning and design that integrates the management of the total water cycle into the urban development process introduced by Government of South Australia. Previous studies shows that rain gardens have been effective in retaining large volumes of runoff and consistently reduced the number of certain pollutants. This article will review some of the guidelines, laboratory studies and filed monitoring of rain gardens that shown great potential for water quantity and quality control improvement. Thus, this that can possibly contribute to the development and implementation of rain gardens in Malaysia under tropical climate. The outcome of the study hopefully can be use to higlight the potential of rain gardens in order to achieve the sustainable urban development in Malaysia. I. RAIN GARDEN SYSTEM Water sensitive urban design (WSUD) is a relatively new approach to responsibly manage urban stormwater runoff [13]. Bioretention systems, also referred to as rain gardens are the simplest form for Water Sensitive Urban Drainage (WSUD) systems. Nowadays, rain gardens system are suggested and have been increasingly popular technology for stormwater management [2]. Rain gardens system used vegetation such as tress, shrubs and grasess or other native plants and often located at low points in landscape. The usage of vegetation is to improve the efficiency of pollutant removal from stormwater. The systems are designed to receive stormwater runoff from impermeable surfaces such as roads, roofs, and parking lots. Rain garden system are layered using soil, sand and mulches. Experts confirmed that that rain gardens have a great potential in reducing peak flow and improve water quality in a natural and aesthetically pleasing manner [5]. Pollutants and nutrients from stormwater runoff are removed by rain garden vegetation soils through a combination of natural physical and biological processes associated with the type of soil and plants used [10]. Rain gardens system are unique compared to most the common types of Best Management Practices, mainly wet and dry pond. These systems also providing aesthetically pleasing landscape. Besides the landscaping aspect, rain gardens have many positive benefits including higher pollutant removal efficiencies for nitrogen, phosphorus, and trace metals and promotes water conservation as the area is fed by stormwater rather than by irrigation. In addition, rain gardens system provide low maintenance as compared to most traditional stormwater BMP’s. II. RESEARCH STATEMENT Rain garden system are considered as a new concept in Malaysia and offers a lots of benefits. As compared with US where rain gardens was widely used [1], Malaysia has initiative to implement rain gardens system although it has different climate regarding to rainfall and temperature. Todays, Malaysia economy has rapidly change throughout the year. Urban development is needed to cater the increasing of urban population. Due to urbanization, the construction of paved area that has significant changed on the hydrologic and hydraulic characteristics of the catchments. For that reason, occurrence of flash flood in urban area in Malaysia is becoming more cruel form year to year. This urban stormwater has negative environmental and ecological effects. Because of this problem, Department of Irrigation and Drainage (DID) Malaysia has introducing New Urban Drainage Manual known as Storm Water Management Manual for Malaysia (Manual Saliran Mesra Alam or MSMA). These manual provide a set of guidelines for new development in Malaysia which adopting natural processes solutions for stormwater treatment. As mention by Zakaria [15], these guidelines set up a new philosophy which is ‘source control techniques’ in order to minimize the runoff flow rate from the contributing area. The manual apply the concept of Best Management Practices (BMP’s) to control stormwater in terms of quantity and quality runoff to achieve zero development impact contribution. Additionally, another good example of Best Management Practise (BMP’s) in Malaysia is the implementation of a Bio Ecological Drainage System which has applied vegetated swale, dry pond, wet pond, and detention pond and wetland techniques. The quality of stormwater has been tested and performance of water quality is in the range of Class І to Class ІІІ based on Water Quality Index (WQI) [6]. There are many design criteria and guidelines has been developed depending on the country and climate. Many studies has been conducted in both laboratory and field studies to assess the perfomance of rain gardens system in reducing the runoff volumes and also pollutant removal. Rain gardens system have proven to reduce runoff voulmes and concerntrations of sediments, heavy metals, phosphorus and pathogenic bacteria by Hatt [2]. This sections will reviews the main findings and beneficial of rain garden system components. Performance of rain garden Performance of rain garden has been tested and analyzed by many researchers. Research done by Lloyd [9] with 125 biofilter columns constructed in greenhouse in Melbourne, Australia to test the performance of stormwater biolfilters for removal sediments. Normally, the presence of suspended solids in storm water indicate the presence of organic matter, heavy metals and other pollutants. The result shows that all the biofilters were highly effective in removing TSS and their performance was consistent over time. A total TSS mass removal was mostly greater than 95% after the test series over all the sampling. This result was similar as reported in previous by Hatt [2]. In comparison, the performance of bioretention systems in field setting in Aucland, New Zealand showed reduction of TSS from stormwater that flowed through the bioretention system. The observation from the study showed that concerntration of TSS was reduced significantly by the bioretention system. Beside removing TSS, rain gardens system can perform positively in removing Nitrogen, Phosphorus and heavy metals as shown in Table 1 below. Table 1 : Previous research on performance of rain garden system