CONSIDERATION OF THE RATIO OF RIVER WATER FROM THE TONE AND ARAKAWA RIVERS IN THE RIVER WATER OF THE TAMA RIVER

Abstract

 The river water in the Tama River includes river water from the Tone and Arakawa Rivers as recycled sewage water. The ratio of river water was estimated to be 17.2% on average per year and 43.1% on the maximum day in 2018. When the flow of the Tama River was insufficient, the ratio of river water was estimated to be 24.0% on average during the year and 44.7% on maximum day. Then, the percentages corresponding to abundant (95-day flow), normal (185-day flow), low (275-day flow), and drought (355-day flow) conditions were estimated to be 18.6%, 26.3%, 29.9%, and 41.9%, respectively. Recycled water in the river water of the Tama River, which originates from the Tone and Arakawa Rivers, is important for maintaining the river water volume, and this condition is maintained by the water cycle of man-made systems such as water supply and sewage systems. From the point of view of the water cycle, it is necessary to clarify the position of the water cycle of man-made systems in the Basic Law on the Water Cycle and its Plan. Furthermore, it is argued that the water cycle perspective should be taken into consideration when discussing the water environment in terms of ensuring the normal function flow, ensuring stable water supply in times of disaster, and investigating the Water Environment Soundness Index.