Monitoring and Modeling of Urbanization Impacts on Groundwater in the Yata River Watershed

The results of simultaneous field observations from October 1999 to November 2000 are shown and compared with those of 1970’s. The results show that during the past 25 years, along with the development of urbanization, groundwater tables in shallow aquifer become a few meters lower. And the nitrate concentrations of groundwater are found to become higher. To estimate the effects of urbanization on groundwater, a distributed hydrological model, which takes the surface and subsurface flow as an integrated system, is applied to the watershed. Firstly, for model verification, the simulation is carried out for the present condition (1998-2000). Comparisons between observed and simulated results are made for both river discharges and groundwater tables, and fairly good agreement is found. Then simulations are performed for the without river improvement condition (river sections before river improvement are used) and the past condition (around 1975). It is concluded that land use changes and river improvement cause major groundwater changes in terms of recharge and groundwater discharge to river.