2017 年 83 巻 848 号 p. 16-00508
In recent years, water quality deterioration at the bottom layer of the lakes and dam lakes becomes a problem. Water quality deterioration is caused by the decrease in concentration of dissolved oxygen at the bottom of a lake. In order to prevent water quality deterioration of the lake, we have developed a dissolved oxygen improvement system. To develop the system, we first realized the necessity to develop a new detector that can detect water and sludge boundary. Since, the backscatter γ-rays can be measured even if the gas is generated from the sludge deposited at the bottom of lake. In addition, it is possible to measure even if the turbidity of water in proximity to the bottom of lake is large. Therefore, we have developed a detector that can detect the sludge surface by measuring the backscatter γ-rays. The sludge surface detector, while dropping in to the lake, continuously monitors the sludge surface in a contactless manner and stores the data to a central database system. The developed sludge surface detector is tested in the river where sludge is deposited and the sludge surface is detected from 70mm before the surface. Thereafter, the developed sludge surface detector has been evaluated at the dam lake using the system of improving the concentration of dissolved oxygen, and the sludge surface detector was succeeded to detect the sludge surface with an accuracy 1 cm.