This report describes runoff control facilities (five years after construction) which are basically an athletic field consisting of tennis courts, constructed in an area of about four hectares in Tokyo. The report is divided into three parts. The first part deals with the social background of the fact that the athletic field has come to have runoff control functions. The second part concerns the summary of these facilities, and then the last part relates to the effects of runoff control. Concerning the effects of the facilities, the return period of design rainfall for runoff control facilities is ten years, but stormwater has been stored on the tennis courts twice in five years after construction. Though these two cases of rainfall were very extraordinary, as the outcome of the inspection of the runoff control facilities we were able to confirm the effects of runoff control by means of simulating under the condition of those two cases of rainfall. In addition, we were able to confirm the effect of groundwater cultivation by means of researching the transition of the groundwater table.
