Probabilistic design of storage capacity for rainwater cistern systems

The paper demonstrates the potential of a rainwater cistern design based on a probabilistic approach. Traditional cistern designs do not allow any wat er shortage. The tank-size design in this study permits the possibility of failure to account for the characteristics of the crop, which must sustain water shortage to a certain degree at infrequent intervals. Sequential peak analyses, combined with the failure probability concept, were adopted in t he analytical procedure. A hilly area in northern Taiwan was selected as th e study site, where water shortage is a severe problem for tea cultivation. Rainfall records and water-demand information were collected for analysis to determine an adequate tank size for a stable water supply. The determina tion of the tank size is related to the rainwater abstraction coefficient, the ratio of the cultivated area to the rainwater collecting area and the f ailure probability. The results are expressed as a regression equation to p rovide a convenient way for farmers to set up cistern systems in this area. (C) 2000 Silsoe Research Institute.