Potential of rainwater harvesting in Nepal : a case study of kathmandu

Abstract

This paper gives an overview of rainwater harvesting system in urban Kathmandu valley (27°32’13”- 27°49’10” N 85°11’31” & 85°31’38”E) that can be harvested during monsoon season (June-August) and use of collected rainwater in dry period so as to minimize the daily water demand among different households. The main study of research is to analyze and interpret the collected rainwater and household catchment area together to know the capacity of individual household of different land sizes. The research ultimately gives the framework of design storage tank depending on amount of rainfall collected from different roof catchment areas. The annual rainfall data of Kathmandu valley (2003-2013) is collected from department of hydrology and meteorology and in a same way roof catchment and land size data of different household in ward-9 were collected from ward office of KMC. The household land size and roof catchment area of different land area (2-4,4-6,6-8,8-10,10-12) anna gives different potential that amount of rainwater can be harvested and which is basis for design of harvesting system. The capacity of collecting rainwater depends on roof catchment area and there is more collection of rainwater as the catchment roof area increases accordingly with respect to land area. The monthly precipitation of Kathmandu valley is more in June – September with monthly precipitation of 215,10mm, 374,909mm, 314,927mm and 244,390mm and average area roof surface of 2-4 anna is 72,66m2 and it increases to 167,38m2 of 10-12 anna. The collected data shows that there is high potential of water harvesting and collected water can be useful domestic resource. The household member gets benefitted with additional water source by the use of simple and easily accessible technology. In a same way there is less water supply pressure to the government and authorized institutional bodies and ultimately beneficial for environmental risk of flooding as well.