1st International Conference on Rain Water Cistern Systems
Honolulu, Hawaii, USA - June 1982

Section 3: Design, Cost, And Policy

Page 128

Determining The Desirable Storage Volume Of A Rain-Catchment Cistern System: A Stochastic Assessment

PingSun Leung & Yu-Si Fok
University of Hawaii at Manoa, USA

Introduction

The four major design factors for rain-catchment cistern systems are rainfall, catchment area, storage capacity and water demand. Of these, only rainfall is uncontrollable by the system designer. In most cases, the size of the catchment area or roof is largely predetermined for an existing structure. The initial basic decision for the cistern owner is to determine the minimum storage capacity which can satisfy the water demand. The minimum storage capacity can be easily determined if given a set of deterministic rainfall for a fixed planning horizon. Most studies (Fok et al. 1980; Wentworth 1959) used the worst rainfall occurrence for the design of the storage capacity without looking into the impact of the stochastic nature of rainfall on storage capacity design. The present study suggests using computer simulation to determine the probability distribution of the minimum storage capacity required. This will provide additional information to the cistern owner in deciding on the necessary storage capacity. The historical rainfall pattern at the Manoa Tunnel station on the island of Oahu was analyzed and used as a case study.

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