Accurate determination of evapotranspiration or evaporation from ground surface is very important to analyze precisely groundwater flow in the unsaturated zone near the surface. Also this determination is important for detailed analysis of moisture movement and pollutant migration near the ground surface because evaporationgive a boundary condition of flow. However, there are not so many knowledge on the evapotranspiration from the actual field. The present authors reported that the evaporation and evapotranspiration from ground surface can be measured using a box type technique with high accuracy and good applicability. In this study, seasonal evapotranspiration changes were successfully measured from an actual grass field. Two places were selected in these measurements, the first is vegetated place and the second is sparsely vegetated place. Evapotranspiration was measured in these places in the all seasons during a year. It was found that the maximum evapotranspiration from the vegetated place in the summer season is about four times of it in the same place in winter season in same year and evapotranspiration from the vegetated place is about three times of it from the sparsely vegetated place in the winter season. The effect of solar radiation or sunlight on evapotranspiration was clarified. It was found that, the radiation has large effect on the evapotranspiration rate. The evapotranspiration rate increases with the increase of solar radiation. Also, the effect of plant density on the evapotranspiration rate was studied. It was found that the evapotranspiration increases linearly in case of white clover plant and the transpiration for this type of plant could be estimated, separately, from the evapotranspiration. Evapotranspiration could be simply and easily determined in all seasons using the box type technique.
A channelised long run-out debris slide triggered by the Noto Hanto Earthquake in 2007, Japan Abstract A strong earthquake (M J 6.9, M W 6.6-6.7) at about 11 km depth hit the western shore of the Noto Peninsula on Honshu, Japan, at about 00:42 coordinated universal time (9:42 A.M. local time) on 25 March 2007 (the Noto Hanto Earthquake in 2007). The earthquake triggered only 61 landslides, with most traveling short distances. It caused one long run-out landslide in the Nakanoya district of Monzen town, Wajima city, Ishikawa Prefecture, when a portion of a deep-seated landslide transformed into a moderate debris slide down a channel. The rock slide occurred on a south-facing convex-shaped slope on a small spur where earthquake ground shaking likely was strongly amplified by topography. A portion of the rock slide reached a small channel floored by materials containing abundant groundwater. Constant-volume box-shear tests on normally consolidated saturated specimens revealed that the apparent angle of internal friction of the channel-floor material was 33-36°at 10-mm shear displacement and did not show much decrease in effective normal stress during shearing. In situ rock-sliding testing on the exposed channel materials showed a low kinetic-friction angle of about 21°. We suggest that an unsaturated portion of the rock slide slid down the channel, with sliding between the rock-slide mass and the channel floor. Because the slope angle of the travel path nearly equaled the kinetic-friction angle, the unsaturated rock slide mass may have traveled at a moderately slow speed, or it might have decelerated and accelerated. Slow speed is supported by accounts from local residents that suggest movement of debris continued for 3 days after the main shock.
As wood pieces supplied by landslides and debris flows are one of the main components of ecological and geomorphic systems, the importance of quantifying the dimensions of the wood pieces is evident. However, the low accessibility of disturbed channels after debris flows generally impedes accurate and quick wood-piece investigations. Thus, remote-sensing measurements for wood pieces are necessitated. Focusing on sub-watersheds in coniferous and broadleaf forests in Japan (the CF and BF sites, respectively), we measured the lengths of wood pieces supplied by landslides (> 0.2 m length and > 0.03 m diameter) from orthophotos acquired using a small unmanned aerial vehicle (UAV). The measurement accuracy was analyzed by comparing the lengths derived from the UAV method with direct measurements. The landslides at the CF and BF sites were triggered by extremely heavy rainfalls in 2017 and 2018, respectively. UAV flights were operated during February and September 2019 at the CF site and during November 2018 and December 2019 at the BF site. Direct measurements of wood pieces were carried out on the date of the respective second flight date in each site. When both ends of a wood piece are satisfactorily extracted from an orthophoto acquired by the UAV, the wood-piece lengths at the CF site can be measured with an accuracy of approximately ±0.5 m. At the BF site, most of the extracted lengths were shorter than the directly measured lengths, probably because the complex structures of the root wad and tree crown reduced the visibility. Most wood pieces were discharged from landslide scars at the BF site, but at the CF site, approximately 750 wood pieces remained in the landslide scars approximately 19 months after the landslide occurrence. The number of wood pieces in the landslide scars of the CF site increased with increasing landslide area, suggesting that some wood pieces can be left even if large landslides occur. The lengths and locations of the entrapped wood pieces at both sites were not significantly changed between the two UAV flight dates. However, during this period, the rainfall intensities around the CF site measured by the closest rain-gauge of the Japan Meteorological Agency reached their second highest values from 1976 to 2019, which exceeded the 30-year return period. This suggests that most of the entrapped wood pieces rarely migrated even under intense rainfall.
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