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9th International Rainwater Catchment Systems Conference
"Rainwater Catchment: An Answer to the Water Scarcity of the Next Millennium."
Petrolina, Brazil - July 1999

Section 4: Technology of Rainwater Catchment Systems

Paper 4.9

Influence of Rainfall Amount and Distribution on Rainwater Catchment System Design

David W. Waweru
Agric. Engineering Department
University of Nairobi
P O Box 30197, Nairobi, Kenya


The analyses of rainfall characteristics form the core of the hydrological design of rainwater catchment system. Of importance are such aspects as rainfall amount, rainfall distribution, length of wet and dry spells, drought severity among others. The coefficient of variation, unlike the standard deviation, does not depend on the annual totals but only on the degree of variation between the monthly totals for each year. Rainfall amount and rainfall distribution are analyzed by calculating the probability of exceedence for each value according to a plotting position formula devised by Weibull.

The results indicate that in the hydrological design of rainwater catchment system, two aspects of rainfall are of paramount importance. These are rainfall amount and rainfall distribution. The hydrological design leads to the determination of the major parameters of catchment area and tank size. This study therefore serves to demonstrate adequately that rainfall amount influence catchment size while rainfall distribution influences the storage capacity.

PDF of full document (4pp, 19kb)

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