Abstract
In recent years there have been several reports published on researches regarding regulating ponds in irrigation systems. All these researches are presumed to share the goal of designing regulating ponds of the kind that will serve to close the gaps between supply and demand in such a way as to allow maximal flexibility in irrigation in terms of both the quantity of water available and access timing. The present paper is an attempt to put these researches in perspective in order to define their relative significance.
Ogata (1984) succeeded in simulating formulaically the interrelationship of the amounts of inflows into regulating ponds, the pond capacities and the gaps between supply and demand. Cho (1984) devised a formula for obtaining pond capacities commensurate with the trapezoidal patterns of water demand peculiar to upland field irrigation. The research by Ezaki (1989) confirmed that the patterns of water demand will present comparably simple profiles. Nishide (1989), dealing with horticulture irrigation, identified the patterns of water demand, the degrees of freedom in irrigation and the ratios of the amounts of discharges via the spillway to those of inflows into the regulating pond. Yoshino (1989) designed a calculation procedure based on the assumption of non?uniform flow in order to determine the design capacity of a so-called buffer pond installed at the site where the open channel system is linked to the pipeline system. Mitsuno's theoretical study (1992) demonstrated that an open channel system inherently has a filtering function of absorbing flow fluctuation. Hirose's statistical study (1989) proposed realistically optimal design criteria for determining the capacities of regulating ponds in pipeline irrigation systems. His proposal was derived from the processing of accumulated data on the actual water balances of several regulating ponds.
The researches by Cho, Ezaki and Nishide mainly dealt with upland field irrigation. On the other hand, those by Yoshino and Hirose presented practical methods of determining pond capacities in paddy irrigation systems. Yoshino's procedure will suit a system in which information about use of a regulating pond can be easily fed back to the management of the gate in the diversion works. Hirose's study addressed the irrigation needs and features of a benefited area where intake operations in the terminal paddy blocks are conducted in a not so finely-tuned way (as is usual in Japanese farming) at an interval of a day or even a few days. His proposal was aimed at enhancing the degree of efficiency and freedom in this kind of irrigation to such a level where any required amount of water is available at any time and is used only when it is needed.
Mitsuno showed that the mechanism underlying the fluctuation absorbing function of an open channel system can be theoretically accounted for in terms of spectrum functions. One implication of his research findings is that further research along his line might provide a comprehensive theoretical framework which would enable us to explain in a unified way a whole set of fluctuation phenomena in irrigation systems. It might also be expected that this theoretical development might finally be technologically reflected in the system design of a user?oriented irrigation unit combining in an optimal way the storage function of an open channel and the regulating capacity of a farm pond.
