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71.
72.
Long-term impact of extra sediment on notches and incised meanders in the Hoshe River, Taiwan 总被引:1,自引:1,他引:0
The extra sediment load induced by typhoons and rainstorms in the Heshe River,Taiwan,are the principal reason for severe sediment-related disasters.The total sediment load during Typhoon Morakot in 2009 was 31 × 106m3,accounting for 95% of the annual sediment discharge.Large amounts of sediment load entered the Hoshe River,causing the braiding index(BI) to increase.Subsequently,the BI became positively correlated with the channel width in the Hoshe River.The specific typhoon and rainstorm events decreased after Typhoon Morakot,the sediment input decreased,inducing the fluvial morphology of the braided river to develop into a meandering river.The extra sediment load induced the deposition depth to increase and produce a headward deposition in the main channel and its tributaries.In addition,the river bend and the topographical notch restrained the sediment from moving downstream and being stored locally,indirectly increasing the erosion density of the river banks from 2.5 to 10.5 times. 相似文献
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Pierre Kaufmann Gérard Trottet C. Guillermo Giménez de Castro Jean-Pierre Raulin Säm Krucker Albert Y. Shih Hugo Levato 《Solar physics》2009,255(1):131-142
The presence of a solar burst spectral component with flux density increasing with frequency in the sub-terahertz range, spectrally
separated from the well-known microwave spectral component, bring new possibilities to explore the flaring physical processes,
both observational and theoretical. The solar event of 6 December 2006, starting at about 18:30 UT, exhibited a particularly
well-defined double spectral structure, with the sub-THz spectral component detected at 212 and 405 GHz by the Solar Submilimeter
Telescope (SST) and microwaves (1 – 18 GHz) observed by the Owens Valley Solar Array (OVSA). Emissions obtained by instruments
onboard satellites are discussed with emphasis to ultra-violet (UV) obtained by the Transition Region And Coronal Explorer
(TRACE), soft X-rays from the Geostationary Operational Environmental Satellites (GOES) and X- and γ-rays from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). The sub-THz impulsive component had its closer temporal
counterparts only in the higher energy X- and γ-rays ranges. The spatial positions of the centers of emission at 212 GHz for the first flux enhancement were clearly displaced
by more than one arc-minute from positions at the following phases. The observed sub-THz fluxes and burst source plasma parameters
were difficult to be reconciled with a purely thermal emission component. We discuss possible mechanisms to explain the double
spectral components at microwaves and in the THz ranges. 相似文献
75.
Hsin-Chi Li Tingyeh Wu Hsiao-Ping Wei Hung-Ju Shih Yi-Chiung Chao 《Natural Hazards》2017,86(3):1039-1058
This study examined the Kaoping River basin, Taiwan, an area severely destroyed by Typhoon Morakot in 2009. Dynamically downscaled data were applied to simulate extreme typhoon precipitation events for facilitating future preparation efforts (2075–2099) under climate change conditions. Models were used to simulate possible impacts in upstream and downstream areas for basinwide disaster loss assessment purposes. The Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability and FLO-2D models were applied to simulate slope-land disaster impacts and sediment volume in the upstream area. The sediment delivery ratio was used to calculate the valid sediment amount delivered downstream and the riverbed uplift altitude. SOBEK was used to build a flood impact model for the Kaoping River basin, and the model was used to simulate potential flooding caused by future extreme typhoon events. The Taiwan Typhoon Loss Assessment System established by the National Science and Technology Center for Disaster Reduction was used to evaluate the potential loss associated with extreme events. The property loss calculation included 32 land-use categories, including agriculture, forestry, fishery, and animal husbandry losses; industrial and commercial service losses; public building losses; and traffic and hydraulic facility losses. One of the Kaoping River basin townships, Daliao District, had the highest flood depth increase ratio (12.6%), and the losses were 1.5 times the original situation. This was much worse than were the losses suffered during Typhoon Morakot. These results also show that sediment delivered from the upstream areas had a significant influence on the downstream areas. This is a critical issue for future flood mitigation under climate change conditions. 相似文献
76.
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78.
Keh-Gong Shih 《Pure and Applied Geophysics》1971,85(1):298-308
Summary The approximate solution for the disturbance of a uniform heat flow in a homogeneous semi-infinite medium by an object of different thermal conductivity buried in it is generally used in the interpretation of heat flow anomalies on the ocean bottom. In order to know the accuracy of the approximate solution, a comparison between the approximate solution and the exact solution is given in the case of a very long horizontal cylinder in a semi-infinite medium. The computed results indicate that the two solutions agree to within 10% whend>1.3 and 0.5<<2, whered is ratio of the depth to the radiusR
0 of the cylinder and is the factor of the contrast of the thermal conductivities between the medium and the body. As for the cases when 1 and 1, the same accuracy can be obtained only whend>2. A similar approach is also applied to the case of a spherical conductor in a semi-infinite medium by using a bispherical harmonic solution. The results of both the bipolar solution and the bispherical solution show that when 1 andd1, the vertical thermal gradient at the surface of the semi-infinite medium is always positive and tends to zero, but a negative vertical gradient may be obtained for the approximate solutions. 相似文献
79.
Total Hg (∑Hg), organic-Hg (O-Hg) and Se bioaccumulations in small cetaceans distributed in Taiwanese waters of the Taiwan Strait and the southwestern Pacific have been investigated for the first time. The results could represent the baseline metal concentrations of marine mammals in the southwestern Pacific, where volcanic activities are possibly the major source of mercury to the environments. Muscle samples of four species of small cetaceans were collected from animals accidentally caught by tuna-longline fisheries from 1994 through 1995. In total, 53 pantropical spotted dolphins, Stenella attenuata, nine spinner dolphins, S. longirostris, five bottlenose dolphins, Turiops truncatus and four Risso's dolphins, Grampus giseus were analyzed. In addition, two stranded pantropical spotted dolphins were investigated. Cold vapour AAS and ICP-MS were used in the analysis of Hg and Se, respectively. Significant species difference was found in the four species of small cetaceans. Among them, the pantropical spotted dolphin showed the highest mean concentration (mg/kg wet wt.) of both ∑Hg (3.64±2.19) and O-Hg (2.79±1.23), whereas the Risso's dolphin had the highest mean concentrations of Se (1.77±1.29). There was no significant sex difference with respect to metal bioaccumulation in the samples of S. attenuata. Significant correlations between body length (BL) and ∑Hg, as well as O-Hg concentrations were observed in pantropical spotted (Sa) and spinner dolphins (Sl). The linear relationships were Sa: ∑Hg=−8.290+0.066BL, r=0.421; Sl: ∑Hg=−2.735+0.025BL, r=0.875; Sa: O-Hg=−3.723+0.036BL, r=0.408; and Sl: O-Hg=−3.017+0.025BL, r=0.870. However, a demethylation phenomenon that decreasing the percentage of O-Hg coupled with increasing levels of Se was observed when the ∑Hg concentrations in the muscle tissues of dolphins reached 4 mg/kg wet wt. 相似文献
80.
D. C.-F. Shih G.-F. Lin 《Stochastic Environmental Research and Risk Assessment (SERRA)》2002,16(5):374-398
The water level of a seawater gauging station and 18 groundwater wells coupled with atmospheric pressure in southwestern
Taiwan are analyzed by using spectral analysis in time and frequency domain. The semidiurnal component is found to be the
most significant signal from the measurement of water level and atmospheric pressure, and the diurnal component is less distinctive
in part of water level and atmospheric pressure record. Although auto-spectral and cross-spectral density functions are significant
in atmospheric pressure and water level, the pressure variations do not significantly affect the seawater and the majority
of groundwater level in the study area with amplitude of time series observations. The astronomical tidal components are likely
the main factor causing seawater and groundwater level to fluctuate in Pingtung, Taiwan. Time lags are estimated from 20 min
to a few hours in aquifers. It concludes that the disturbance on groundwater levels from the effect of oceanic astronomical
tide is different from the varying hydrogeological characteristics of aquifer. In this study, the spectral analysis of water
level in time and frequency domains gives strong indications of sensitive variations to water level fluctuation.
This research is supported by the Institute of Nuclear Energy Research (INER), AEC, Taiwan, Republic of China, under a fund
from Executive Yuan. The authors thank Taiwan Central Weather Bureau and Taiwan Provincial Government Water Resources Department
for providing useful data. 相似文献