Soil moisture plays an important role in cli-mate change, water-energy cycle and vegetation change. This study mentioned the current conditions of soil mois-ture observations in CEOP, GEOSS and earth observa-tion satellite missions and then discussed some results of ground-based soil moisture observation in the study area of AMPEX/MAVEX/CEOP in the Mongolian plateau and AMSR-E soil moisture estimation in Asia. We got that it is very important and useful for CEOP and GEOSS to monitor soil moisture by ground-based stations and earth
We examined effects of soil water repellency on hydrological processes in various scales from small plot to catchment in a Japanese cypress plantation. We measured soil water repellency and infiltration rate along a hillslope transect, and monitored overland flow at small plots (1 × 2 m) with sparse and dense fern cover and a large plot (8 × 25 m) and stream discharge at the outlet of a small catchment (0.43 ha). Strong water repellency in surface soil horizon was partially associated with Hortonian over-land flow, which volume potentially depended on sever-ity of water repellency. Relationships between matric po-tential and soil water content indicate that changes in the soil water repellency and consequently runoff coefficient of overland flow could occur during a single storm event. Greater amounts of overland flow at small plots compared to ones at large plot suggests that overland flow generated in hillslope was discontinuously transferred. Higher infil-tration rate at the bottom of hillslope likely caused little contribution of overland flow on catchment runoff. Despite the substantial overland flow generated in hillslope due to soil water repellency, water repellency was not a dominant factor accelerating runoff directly at the small catchment scale.
In order to establish the sustainable urban wa-ter cycle, it is necessary to evaluate potentials of utilizing secondary effluent and road runoff as self-owned water re-sources in urban areas. Groundwater replenishment by in-filtration of secondary effluent and rainwater is a promising option to secure self-owned water resource in urban area. Therefore, it is expected to understand the dynamic change of their water quality and to assess the risk and the accept-ability for water use. In this study, we conducted soil infil-tration column tests for secondary effluent and road runoff to evaluate the treatment performance. Furthermore, we proposed the comparative representation of water qualities of percolating water with those of rivers throughout Japan so that citizens could understand their water quality risk and acceptability for water use.
To establish a method to monitor the vertical profile of volumetric water content (θ) near soil surface, a multi-wire profile probe (MWP probe) was designed and applied to the θ-profile observations during the evapora-tion processes in sand and decomposed granite soil. The probe consists of eight sets of the 3-wire TDR (time do-main reflectometry) probes, which are attached to a print-circuit board with a low permittivity, and is capable of measuring relative permittivity (εmwp) at intervals of 3 mm. The relationship between εmwp and θ for sand did not agree with one derived from Topp equation because the board had the influence on the εmwp measurements. Thus, we calibrated the probes for sand with different moisture con-ditions and found that the probes can determine θ within acceptable accuracy. In the evaporation processes, the ob-served θ-profiles showed that the moisture contents for sand at 3 and 6 mm depths locally decreased in the initial stage of the process, while the moisture contents for de-composed granite soil uniformly decreased at any depth. We concluded that the designed MWP probe would be useful for millimeter-interval measurements of vertical θ-profiles near soil surface.
A laboratory experiment was carried out to in-vestigate the sedimentation characteristics of Tondano lake clay and effect of gypsum addition, included the settling patterns as the previous experiments. Firstly, the floccu-lation and dispersion characteristics, which are evaluated by turbidity, are substantially influenced by pH and salin-ity. Then, it was found that the addition of 5 % gyp-sum to this clay influenced the settling pattern and set-tling/consolidation rate. In the region in which consolida-tion settling does not occur (above 3000 % water content), the effects of gypsum addition on the settling patterns are significant; whereas in cases that the consolidation settling occurs (under 2000 % water content), the effects of gyp-sum addition are not so much significant. The greater wa-ter content of the clay suspension could induce a higher degree of flocculation, thus explaining sedimentation char-acteristics induced by gypsum treatment.
In initially dry coarse soil, it is noted that a uniform and nonponding surface water flux causes an un-table wetting front when the flux rate (q0) is less than the saturated hydraulic conductivity (Ks). To investigate the relationship between q0 and the pressure gradient with time (∂h/∂t) in the wetting layer under the condition of unstable water flow, we carried out one-dimensional infil-tration experiments by applying non-ponding water fluxes to the surface of soil packed homogeneously in an acrylic tube. We filled the tube with four different soils; sand, volcanic clay soil, loam and silt and installed microten-siometers to measure pressures in these materials. The re-sults showed that (1) negative pressure head gradients with space (∂h/∂ z) and time(∂h/∂t) appeared clearly only for sand and Eq. (1) derived by Cho et al. (2005) agreed well to the pressure measurement with time, (2) the ∂h/∂t was provided as a quadric function of q0 shown as Eq. (4) and fitted well the experimental data for sand . From this equa-tion, it was found that the smaller q0 becomes, the closer∂h/∂t approaches 0 and the flow becomes more stable. This trend could explain the experimental results of Yao and Hendrickx (1996).