PROBLEM TO BE SOLVED: To provide a ground installation of a green zone, capable of utilizing naturally supplied rain water to a maximum possible extent and capable of decreasing irrigation conducted by irrigation facilities requiring cost and energy quantitatively depending on the irrigation to a minimum necessary extent, by estimating frequency of rainfalls expected from meteorological data in the past, when the green zone is installed by utilizing a rooftop of a building, and therefore capable of being installed at a low cost friendlily to the global environment, and further capable of keeping water quality stable, by surely replacing water in a reservoir. SOLUTION: In this installation, an elevated position of a tip of an electrode pole 7b for detecting a water level of stopping water supply is set to such an elevated position as to be higher than an elevated position of a tip of an electrode pole 7c for detecting a water level of starting the water supply and to be capable of detecting a water level of starting water drainage of a pallet 15, and an alienated interval in a vertical direction between the elevated position of the tip of the electrode pole 7b and the elevated position of the tip of the electrode pole 7c is set based on a value calculated by a prescribed calculation formula in which the frequency of the rainfalls in a predetermined region and an amount of water consumed and evaporated in a plantation area are used as variables. COPYRIGHT: (C)2006,JPO&NCIPI
