Role of Roof–top Water Harvesting to Manage Drought in Bankura District of West Bengal

Abstract

In the present work, draught prone region of Bankura district is selected for the analysis of feasibility and sustainability in developing participatory and coordinated systems of roof-top water harvesting. In the present study area, subsurface sources of water are not equally accessible to all. Withdrawal of subsurface water requires huge investment and technology to get access to deeper aquifers. Dug wells at shallow aquifers become dry in lean season and most of them have to experience the hardship of collecting water. A detailed survey with structured questionnaire is made for analyzing the extent of problem and to estimate the demand for water per household per day through the assessment of adult and minor constituents of population, family composition etc. The feasibility of roof top water collection is assessed through examining constructionmaterials of roofs and calculating the daily yield of water-discharge from roof top of average size (calculated from sample survey) in relation to daily rainfall as an average of past 35 years (1969-1991; 1995-1996; 2006-2011). Survey shows that as much as 83% of surveyed houses have either tin, tiles, asbestos or cement roof, having a yielding capacity of more than 90%. The daily amount of water yield from roof top and that of daily demand are plotted in a graph to construct Mass Curve for calculating the reservoir size for a family of four members to meet average demand in dry period Mass curves are constructed by plotting cumulative demand of domestic water for drinking and cooking (60 L/Household/Day) and cumulative supply from the average roof top of 10mx5m size from average daily rain. Considering the possibility of climatic fluctuation, the effective reservoir sizes are designed to meet the demand of worst drought in certain recurrence interval. Log probability analysis shows that the reservoir size of 4025, 5130, 6445 and 7835 L may serve the demand that may recur at recurrence interval of 2, 5, 20, 50 and 100 years.