Recently, many reports have been published about the groundwater environment problems caused by human activities. We have to consider the concept of groundwater preservation toward the next century to supply safe and enough water resources for our descendants. The 2nd joint symposium of Japanese Association of Hydrological Sciences and Japanese Association of Groundwater Hydrology was held on May 28, 1998 at the University of Tsukuba, Japan, with the title of “Present and future groundwater environment and the proposals for the 21st century”. The author reported the proposals for the groundwater preservation toward 21st century through the view point of hydrological cycle, suggesting the importance of the groundwater flow system study to the better management of groundwater resources. In the text, to understand the regional scale groundwater flow system, the author stressed on the importance of the complemental use of the numerical groundwater flow simulation with the help of in-situ groundwater potential measurements and of the environmental isotope information in the groundwater.
A progressive rise in groundwater level has been reported in several major cities in the world. The principal cause of the rise is the reduction of groundwater abstraction which is mainly controlled by groundwater management through economic activities and governmental regulations for groundwater use. Another important cause of the rise is leakage from water supply networks.
In central Tokyo, over the last thirty years, the groundwater level has risen more than 30 m. In addition, about 380 thousand tons of drinking water was estimated to have leaked per day from water mains from 1994 to 1996, and this value is much larger than the volume of rainfall infiltration into the ground.
A rise in groundwater level gives us benefits such as rebirth of dried springs, recovery of polluted river water, appearance of aquatic animals and plants, securement of emergency water, etc. However, the rise possibly produces negative effects on our daily life environment, traffic facilities, underground foundation and structures. Actually, flooding of building basements, leakage into sewers and subway tunnels, increase in hydrostatic pressures on basement structures, reduction of slope stability and so on caused by the rise have been reported in several major cities.
In most cases, the rise in groundwater level would lead to unexpected situations, because cities have rapidly developed and spread when groundwater level was so deeper than that in the present days. We need to establish new groundwater control policy and action schemes against the rise in water level to diminish risks and create better environment.
Preliminary GLobal Imager experiment at Environmental Research Center (PGLIERC) was carried out as a preliminary ground-based experiment of Global Image (GLI) boarded on Advanced Earth Observation Satellite-II (ADEOS-II) which will be launched in 2000. PGLIERC has four main objectives: 1) validation of the estimation of physical properties on the ground using multi-spectral satellite data, 2) reconsideration to relationship between satellite data and ground-based data (in particular in the hydrological aspect), 3) monitoring of the temporal variations in the combinations of Vegetation Indices (VIs) and surface temperature (Ts) at “real scale”, and 4) monitoring and modeling of Bidirectional Reflectance Distribution Function (BRDF). Study field is grassland, located in the Environmental Research Center, University of Tsukuba. This field has a meteorological tower of 30 m height. Some preliminary findings in PGLIERC are summerized as follows.
1) Seasonal changes in spectral reflectances in visible and near infrared were quite different from each other. 2) Vegetation indices derived from in-situ observation represented phenology of the grassland. 3) Vegetation index derived from a spectrometer by the tower observation was similar to that from the in-situ observation. 4) The inclination of VI/Ts relationship, estimated from grid measurements, steepened with the drying of the soil. 5) A hot spot effect was confirmed from the BRDF measurement.