International Rainwater Catchment Systems Association
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4th International Conference on Rain Water Cistern Systems
Manila , Philipines - August, 1989

Section F: Hydrological Data And Analysis

Paper F.2

Establishing Normal Monthly Rainfall For Rain Water Cistern System Design

A. Lo and S.H. Chiang
Chinese Culture University, Taiwan


To properly design and operate a rain water cistern system, it is necessary to understand the dynamic and stochastic nature of rainfall processes. These processes are greatly influenced by random variations as well as cyclical effects. However, there is no general theory available which establishes the length of record required to provide a representative normal period o£ rainfall. The purpose of this study attempts to establish such a value.

To investigate the variability of monthly rainfall over a long period of time, an island station on the Pacific (Western Samoa) was selected for a number of statistical tests. The length of records required was first computed by the stability of mean approach. The number of years necessary to reach different stability levels were established for each month of the year. For locations lacking long-term rainfall records, a relationship between the years of average and the tolerance limit at different confidence levels was developed using the classical statistical approach. A rough estimate of the required length of the most important input variable (rainfall) would aid in the design and operation of a rain water cistern system.

PDF of full document (15pp, 280kb)

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