International Rainwater Catchment Systems Conference
Mannheim, Germany - September 2001
Rainwater Catchment in Humid and Arid Regions
Rainwater as a Supplementary Source of Water Supply in Nigeria
Joseph A. Adelegan
Department of Civil Engineering
University of Ibadan
Over the years, the Federal Government of Nigeria has made appreciable
investments towards development and management of water supply using large
centralised and conventional water supply systems. For certain reasons,
the demand for safe drinking water service continues to overwhelm the
delivery. Though for centuries, people across Nigerian urban and rural
areas have harvested rainwater for household, livestock and agricultural
uses but lack of promotion had limited its wide acceptance especially
in urban centres. The study looks into rainwater availability, rainwater
catchment, storage tank capacity and rainwater quality.
Major data used for the work include an average of 35 years rainfall
pattern based on yearly rainfall intensity for 18 Nigerian cities and
major towns obtained from Nigerian Meteorological Centre records. The
variations and distribution of rainfall in the cities and towns studied
were plotted. Permanent roofs for rainwater harvesting were also assessed.
Moreover, the issue of rainwater quality was also considered.
It appears that the average yearly rainfall in Nigeria during the period
examined varied from 1070mm to 2400mm, that is, 1.07 to 2.40m3 of rainwater
was available per m2 of catchment area each year for the development of
a rainwater based water supply system. A study of suitable permanent roofs
for rainwater harvesting shows that over 75% of urban households and about
20% of rural households have suitable roofs.
A rainwater availability mass curve and cumulative consumption / demand
of total rainwater revealed a shortfall of 0.32m3 in the dry periods and
an excess of 0.22 m3 during rainy season. Hence, for full utilisation
of rainwater potential, a storage tank capacity of 0.54 m3, that is 33%
of the cumulative rainwater is required for an uninterrupted water supply
at a constant rate during the year.
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