Measurement of groundwater table in shallow boreholes

Seno, Shoji; Kurikami, Hiroshi  ; Yabuuchi, Satoshi; Hara, Minoru

Horonobe Underground Research Laboratory of Japan Atomic Energy Agency has been investigating surface hydrogeological features in and around the Horonobe Underground Research Laboratory (URL) area as a part of Horonobe URL project. The objective of measurement of groundwater tables in shallow boreholes is to understand the distribution of the groundwater table and its seasonal fluctuation that will be boundary conditions of a groundwater flow analysis. This report shows the results of the measurement since December 2003 to October 2005 every few month and discussion on the surface hydrogeological features. The results are as follows: (1) The real watershed between the Shimizu river basin and the Penke-ebekorobetsu river basin exists a little to the south of the geographical watershed among the monitoring line. (2) Snow fall/melting is the largest impact on the annual fluctuation of the groundwater table, while influence of precipitation is temporal. (3) The amplitude of the fluctuation of groundwater table depends on the location. (4) Peak level of groundwater table after precipitation is gentler than that of the river water table and appears two or three days later.