Chemical study of the stream water was continuously conducted from March, 2000 to November, 2003 in forested headwater catchment at Ina, Nagano Prefecture. Chemistry of stream water changed at the rain events and the snow melt season, as increase runoff. When temporary runoff was increased by the rainfall, the decrease in the pH was observed as episodic NO₃^- concentration increased. The precipitation element was becoming about 40% in the peak of runoff, result of the two component hydrograph separations. In the snow melt season, NO₃^- concentration was episodic increased with increased runoff at the early stage, however NO₃^- concentration was decreased with increased runoff. The mass balance in the catchment was calculated. The discharge of cation and SO₄^2-­ was more than deposition. On the other hand, the NO₃^- deposition was more than discharge. The discharge and deposition of Cl^- was balanced.

The understanding of the subsurface temperature distribution should be an important step in the designing of geothermal heat-pump systems. Since the subsurface temperature distribution is strongly affected by groundwater flows, it is necessary to understand the flow patterns of the groundwater at study area.

Since there are no observation wells in the Akita Plain, Northeast Japan, we can not grasp subsurface temperature distribution in this plain directly. We applied 3-D groundwater flow and heat transport analyses under simplistic boundary conditions to estimate regional shallow subsurface thermal structure.

As for hydrological survey, chemical compositions and stable isotope data (δD and δ ¹⁸O) of groundwater were collected from shallow wells, snow-melting system wells, rivers and springs. Analyzed 3D groundwater flow systems were validated with the groundwater flow system in this plain estimated by observed hydrological data.

The result of heat transport analysis under the condition of analyzed groundwater flow regime showed that subsurface temperatures increase toward the central part of the plain. Snow melting systems are installed in the central part of the Akita City and we observed temperature-depth profiles in the local area. Analyzed shallow subsurface thermal structure was consistent with observed temperature data including the tendency of observed one.

This study showed the possibility of the estimation of regional shallow subsurface temperature structures using numerical simulation and hydrological method in an area with limited observation wells.