Abstract
The determination of design reservoir capacity requirement is generally based on probability analysis using estimated yearly capacity requirements. It is a prerequisite for this type of analysis that the values are independent of each other. This study sets out to determine and evaluate the critical water demand levels of ten reservoirs throughout Japan, that is, the water demand level up until where yearly capacity requirements remain independent. The reservoirs are selected under the condition that their inflow records indicate the natural discharge from the catchment areas with little influence of human activity.
For this purpose, the authors vary water demand levels from 5% to 100% of long term average river flow. Intervals of 5% are used. The relationship between the level of demand and the magnitude of capacity requirement (MCR) is also discussed.
The results obtained are as follows:
1) The critical levels at the ten studied reservoirs range between 40% and 85%. These values are determined not only by the minimum of annual flow, but also by the sequence of annual flows
2) The MCR curve shows sudden and rapid increase when the water demand level exceeds the critical level, while the shape of the MCR curve is approximately parabolic below this level.
