Yearly Variation of Groundwater Level and Quality in Wells for Using Snow Melting Facilities

supervisor Hirofumi TOYOTA

Recently, local severe rain, which is heavy rainfall in a short time in the limited region, has happened frequently. Especially, the unexpected local torrential rain called °»Guerrilla°… downpour in Japanese has been also generated from 2006. Although a clear definition of the local severe rain is not in the meteorology, the case to exceed 50 mm per hour rainfall in area from ten to several ten km is roughly defined as the local severe rain. A disaster induced by the local severe rain domestically occurs every year for six years from 2003 to the present, and the number of the disasters goes up to eight times.
The 7.13 Niigata flood disaster (Niigata and Fukushima heavy rainfall) occurred in July 2004 is still fresh in our memory as the local severe rain of Niigata. It heavily poured from the night of 12 July in Chuetsu area of Niigata prefecture and Aizu city of Fukushima prefecture, and the total amount of rainfall exceeded 400 mm in former Tochio city (present Nagaoka city) and former Shitada village (present Sanjo city). The flood damage has frequently happened in Mitsuke city because the rainfall is too much to exclude its rainwater to the river etc. using drainage facilities in recent urbanised town.
From that situation, the possibility to inject directly rain water into the wells for snow melting facilities is proposed considering a environmental measure against heavy rainfall, which is low-cost and also effective for prevention of ground subsidence.
It was demonstrated that the capacity to store the pouring water was high in wells for snow melting facilities from previous study. Then, the new study, that is °»Yearly variation of groundwater level and quality in wells for using snow melting facilities°…, was conducted in order to grasp the differences in water qualities between rain and ground water.
The results obtained from the study is shown below.
1)The groundwater level is greatly related to the amount of snowfall. When there is snowfall, the groundwater level decreases because the ground water is pumped up to melt the snow. When there is little snow, the ground water level gradually increases.
2)The pH of underground water is higher than that of rain water, it almost the same as the tap water. The specific electric conductivity of the ground water are also higher than that of rain water. Therefore, the ground water contains a lot of electrolyte ions.
3)It is difficult to pour the rain water in a well directly because its turbidity rises when the rain water passed the road and drainage. Although the turbidity of rain water passed the roof is lower than that of the rain water passed the road and drainage, the value of the pH is low and acidity.
4)When the rain water is directly poured in a well, the effect on soil microorganism should be considered because the dissolved oxygen is high in the rain water comparing with the groundwater.
Next, the seasonal change in water quality of rain and groundwater will be grasped through the yearly measuring in series. Moreover, the effect of pouring rain water on the groundwater will be quantified by examining the quality of the groundwater mixed with rain water.

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