Development of a Rainwater Tank Sizing Calculator for Rainwater Harvesting Application in Southwest Nigeria

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Author(s) T.P. Abegunrin | A.Y. Sangodoyin
Pages 166-174
Volume 6
Issue 5
Date May, 2016
Keywords Rainwater, Tank Sizing, Household Size, Consumption, Southwest, Nigeria

Abstract

Rainwater harvesting (RWH) as a source of potable water supply is gaining prominence in the South-west Nigeria due to increase pressure on conventional sources of freshwater due to population increase and complexity in lifestyle. Reliability of RWH depends on adequate understanding of water demand, quantity of harvestable water, rainfall pattern and storage. The determination of storage capacities varies from one location to the other and from one house to the other within the same location as a result of variations in in rainfall depth, water consumption, roof material and roof size. A tank sizing calculator is needed. This work was designed to produce a tank sizing calculator for rainwater storage in southwest Nigeria. Rainfall data for a duration of 27 years in selected parts of South-west Nigeria (Abeokuta, Akure, Ibadan, Ikeja and Osogbo) for estimation of rainfall depths and distributions were collected from Nigerian Meteorological Agency, Oshodi, Nigeria. Data on household size, water consumption and roofing material were collected from 2500 randomly selected households in the study area using structured questionnaire. The highest rainfall depths of 196, 180 and 65 mm, respectively for Abeokuta, Ibadan and Ikeja occurred in June while 230 and 222 mm for Akure and Osogbo, respectively occurred in September. Average household size was 9 persons with average water consumption of 55±10 and 70±13 l/h/d during the dry and wet season, respectively. About 69% of the houses have galvanised iron sheet, 28% asbestos and 3% other roofing materials. Roof size varied considerably. Galvanised iron sheet roof areas (C_r=0.9) required to harvest rainwater to be stored for 150 days for household size of 7 in Abeokuta, Akure, Ibadan and Ikeja are 35.36, 28.79, 32.67, 25.51 and 30.86 m2, respectively. The developed tank sizing calculator is capable of determining roof area to be guttered and storage capacity required at any level of satisfaction desired under different conditions of household size, water consumption, roofing material and roof size.

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