Storage Volume and Reliability of Rainwater Harvesting in the Coastal Areas of Bangladesh Using a Daily Water Balance Model

Abstract

Scarcity of fresh water has become a thing of concern around the world. Now, in developing countries this necessity has become a priority to be addressed like never before. Having population on the up rise in one hand and declining of fresh water resources on the other, necessity of finding an alternative source of fresh water has become the foremost priority in the world, let alone developing countries. Rainwater is one of the purest water sources on earth and harvesting rainwater has been found to be the most sustainable method of collecting fresh water. In developing countries like Bangladesh rainwater harvesting can provide an effective alternative source of fresh water, especially in the coastal areas where fresh water is scarce due to salinity in the ground water and surface water. These areas have a lot of rainfall that can be used for household and drinking purposes. Although agriculture and industrial water demand may not be fully satisfied by rainwater, drinking and household purposes may use rainwater without any question. But not too many studies have been conducted regarding this. People in this region although are using this technology but the tank sizes are not determined based upon their demand. For the purpose of storage volume and reliability analysis of rainwater harvesting in the coastal areas of Bangladesh a daily water balance model was obtained. Three daily rainfall data; Dry, Wet and Average year condition was used for developing the design curves and the reliability analysis. For the conduction of reliability analysis, catchment area and demand was increased and the results were observed from a spreadsheet. The analysis was done for household water demand only and for that reason a family of 6 members was selected as a typical family. A co-efficient factor of 0.9 was used in all these cases. In brief for a six person household scenario, almost 96% reliability can be achieved by a catchment area of 40 m² and a tank volume of 500 to 5000 liters in an average year condition. For a wet year condition almost iii 80% reliability can be achieved by a catchment area of 40 m² and a tank volume of 500 to 5000 liters. And for, dry years 73% reliability can be achieved for the similar condition. The analysis confirmed that rainwater can effectively meet the needs of the people in this region. More studies must be conducted on this matter but for now, it can be said that, rainwater harvesting can be more efficiently undertaken to solve the fresh water scarcity problem in the coastal areas of Bangladesh.