3 rd International Conference on Water & Flood Management (ICWFM-2011) POTENTIAL OF RAINWATER HARVESTING IN DHAKA CITY Md. Mafizur Rahman 1 , Sazia Afreen 2* and Mohammad Asad Hussain 3 1 Professor, Department of Civil Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka-1000, Bangladesh, e-mail: mafizur@gmail.com 2 Asst. Engineer, DWASA and Graduate Student, Department of Civil Engineering, Bangladesh University of Engineering and Technology (BUET), Dhaka-1000, Bangladesh, e-mail: sazia0004@gmail.com 3 Asst. Professor, Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh, e-mail: asadh@iwfm.buet.ac.bd ABSTRACT Water resources are fast depleting in urban areas due to rapid increase in population and unrestricted use of water. Optimization of water usage and the conservation of water as a natural resource can help to overcome water shortage. This study focuses on the potential of Rain Water Harvesting (RWH) in Dhaka City. At first, long term rainfall analysis of Dhaka has been done. Analyses of rainfall data show that average rainfall of 55 years (1953-2007) in Dhaka is 2073 mm, whereas the same for recent 12 years (1996-2007) is 2166 mm. Decadal rainfall analysis considering rainfall data of 55 years for five consecutive decades (50s, 60s, 70, 80s and 90s) and for the period of 2000 to 2007 shows an increasing trend of rainfall in the recent decades. From the mass curve (rain water availability vs. time) analysis of Dhaka city, it is found that maximum 0.38m 3 of water deficit occurs during the month of April on the other hand 0.25m 3 of maximum excess water is available during October. In this study, contribution of rainwater in meeting water demand of Dhaka city has also been analyzed. Results show that 33% water demand can be met through RWH with individual harvesting system and 10% water demand can be met with community based RWH system. Finally from roof size distribution of different wards of Dhaka city, a method has been presented using GIS to identify the potential areas where RWH can be adopted for partial fulfillment of water demand. These analyses suggest that, in Dhaka, RWH system can be used in conjunction with conventional water supply system to improve the present water scarcity. Keywords: Dhaka City, Rainfall, Rainwater Harvesting, GIS. 1. BACKGROUND Dhaka, the capital of Bangladesh is one of the most populated cities in the world with a population of 10 million in an area of 1528 sq. km. (Rajuk 2004). Many people from the whole country are forced to move from rural areas to the urban areas due to natural disasters like river erosion, cyclone and dry spells. For massive migration of people towards urban areas, population density in Dhaka city is increasing day by day, thereby putting enormous pressures on urban infrastructure, economy and service delivery systems of the city. A comparison of urban population density of Bangladesh between 1991 and 2004 is shown in Figure 1. From this figure it can be observed that even though population density is very high in Dhaka City Corporation, growth rate is highest in Dhaka Mega city (12.4%)