A novel hysteresis model in unsaturated soil     

Han‐Chen Huang  Yih‐Chi Tan  Chen‐Wuing Liu  Chu‐Hui Chen 《水文研究》2005,19(8):1653-1665

This study presents a novel hysteresis model based on van Genuchten's soil‐moisture relationships. The proposed model yields a series of closed‐form relationships in which two shape factors α and η are determined from the main drying and wetting curves. Experimental and literature‐cited data were used to assess model accuracy. The proposed model was also compared with the Scott and KP models. Analytical results indicate that the present model is simple, accurate and effective in constructing the series of wetting and drying scanning curves. Notably, the proposed model outperforms the Scott and KP models in terms of model accuracy. Moreover, the novel model eliminates the pumping effect and has perfect closure at scanning curve reversal points. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

The value of updating ensemble streamflow prediction in reservoir operations     

Hyung‐Il Eum  Young‐Oh Kim 《水文研究》2010,24(20):2888-2899

This study proposes a new monthly ensemble streamflow prediction (ESP) forecasting system that can update the ESP in the middle of a month to reflect the meteorological and hydrological variations during that month. The reservoir operating policies derived from a sampling stochastic dynamic programming model using ESP scenarios updated three times a month were applied to the Geum River basin to measure the value of updated ESP for 21 years with 100 initial storage combinations. The results clearly demonstrate that updating the ESP scenario improves the accuracy of the forecasts and consequently their operational benefit. This study also proves that the accuracy of the ESP scenario, particularly when high flows occur, has a considerable effect on the reservoir operations. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Permineralization process promotes preservation of Holocene macrofossil charcoal in soils     

Guillaume De Lafontaine  Pierre‐Luc Couillard  Serge Payette 《第四纪科学杂志》2011,26(6):571-575

The use of macrofossil soil charcoal as a palaeoecological tool to reconstruct past vegetation, climate or fire history has gained much interest in recent years. Yet little is known about taphonomy of charcoal in soils. Here we assessed the putative loss of palaeoecological information due to charcoal fragmentation after burial. We found no significant loss of charcoal mass with time. Instead, we found a significant positive relationship between the mass of charcoal particles and their age. Permineralization of charcoal particles older than ca. 5200 a explained the increased charcoal mass with time in mineral soils. The permineralization process increased the density of charcoal particles (resulting in a twofold particles mass increase) and thus offers a protection against subsequent degradation. Our results suggest high stability of palaeoecological information from charcoal macrofossils buried in mineral soils at least over the Holocene timescale. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

The Palaeocene “top chron C27n” transient greenhouse episode: evidence from marine pelagic Atlantic and peri‐Tethyan sections     

Jaume Dinarès‐Turell  Victoriano Pujalte  Kristalina Stoykova  Juan I. Baceta  Marin Ivanov 《地学学报》2012,24(6):477-486

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Relationships between primary productivity and bottom‐water oxygenation off northwest Africa during the last deglaciation     

Helena L. Filipsson  Oscar E. Romero  Jan‐Berend W. Stuut  Barbara Donner 《第四纪科学杂志》2011,26(4):448-456

The upwelling region off northwest Africa is one of the most productive regions in the world ocean. This study details the response of surface‐ and deep‐water environments off Mauritania, northwest Africa, to the rapid climate events of the last deglaciation, especially the Bølling–Allerød (15.5–13.5 ka BP) and Younger Dryas (13.5–11.5 ka BP). A high accumulation rate gravity core GeoB7926‐2, recovered at ～20° N, 18° W, was analysed for the grain size distribution of the terrigenous sediment fraction, the organic carbon content, diatom and benthic foraminifera communities. Humid conditions were observed during the Bølling–Allerød with a high contribution of fluvial sediment input. During the Younger Dryas intensified trade winds caused a larger sediment input of aeolian dust from the Sahara and more intense upwelling with higher primary productivity, as indicated by high diatom concentrations. The abrupt and large increase of organic matter caused low oxygen conditions at the sea floor, reflected by the poor benthic foraminiferal fauna and the dominance of the low‐oxygen‐tolerant foraminiferal species Bulimina exilis. This is surprising since low‐oxygen conditions have not been recorded during modern times at the sea floor in this region, despite present‐day intensive upwelling and high primary productivity. After the Younger Dryas, more humid conditions returned, diatom abundance decreased and B. exilis was replaced by typical deep‐sea species as found in the region today, indicating the return of more oxygenated conditions at the sea floor. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Application of the exact constitutive relationship of modified Cam clay to the undrained expansion of a spherical cavity     

Vincenzo Silvestri  Ghassan Abou‐Samra 《国际地质力学数值与分析法杂志》2011,35(1):53-66

The modified Cam clay (MCC) model is used to study the response of virgin‐compressed clay subjected to undrained triaxial compression. The MCC constitutive relationship is obtained in a closed form. Both elastic and plastic deviatoric strains are considered in the analysis. The solution allows to obtain total and effective stress paths followed by the clay in undrained spherical expansion. Pore water pressures are determined from the difference between total and effective mean stresses. For illustration purposes, the analysis is also applied to the well‐known reconstituted normally consolidated London clay and the results are compared with the recently published data obtained by a numerical approach. In addition, the Almansi large strains are used in the analysis, as these allow to obtain limit expansion and pore pressures, whereas both small‐strain and logarithmic‐strain approaches do not permit to determine them. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Testing inferences from palaeocurrents: application of zircon double‐dating to Miocene sediments from the Hengchun Peninsula,Taiwan     

Linda A. Kirstein  Andrew Carter  Yue‐Gau Chen 《地学学报》2010,22(6):483-493

Detrital zircon provenance studies that combine low‐temperature fission‐track and high‐temperature U–Pb single‐grain age dating are powerful in constraining sediment provenance by documenting the tectonothermal evolution of the sediment source(s). We apply these techniques to Miocene (12–6 Ma) sandstones of the Hengchun Peninsula, southern Taiwan, which, based on diametrically opposite palaeocurrents, have a controversial provenance. U–Pb grain ages range from the Miocene (8 Ma) to Archaean (2.5 Ga). Cretaceous thermal cooling is recorded by detrital zircon fission tracks at Loshui and Lilongshan. Permian fission‐track grain ages account for <33% of zircon ages from Loshui, while at Lilongshan, Jurassic/Triassic grain ages account for 33–66% of all zircon fission‐track ages. Minor (<12%) Miocene age components are detected in both formations. These new data suggest that the primary sources of these Miocene sediments were similar. A simple model is proposed invoking sediment reworking in this complex tectonic setting. Terra Nova, 00, 000–000, 2010  相似文献   

It goes both ways: measurements of simultaneous evapotranspiration and fog droplet deposition at a montane cloud forest     

E. Beiderwieden  V. Wolff  Y.‐J. Hsia  O. Klemm 《水文研究》2008,22(21):4181-4189

Fluxes of latent heat, sensible heat, and water vapor, including turbulent deposition of fog droplets, were measured for two months in autumn 2005 within a subtropical montane cypress forest in Taiwan. The goal of the study was to determine whether significant evapotranspiration can occur during foggy conditions. Water vapor fluxes, Q_W, as determined with the Bowen Ratio method, were compared to those simultaneously measured with the eddy covariance method. The median Bowen Ratio was 1.06, and the median Q_W flux was 5 · 2 × 10^?5 kg m^?2 s^?1. The vertical gradients of temperature and specific humidity over the forest, ΔT and Δq, peaked around noon during days without fog, and were reduced during foggy conditions. For 66% of the data points, ΔT and Δq were negative, corresponding to positive (upward) fluxes of sensible heat Q_H and latent heat Q_E. A Monte Carlo simulation proved that statistically significant evapotranspiration rates, i.e., upward water vapor fluxes, occurred during fog. At the same time, deposition fluxes of fog droplets occurred. Our results show that even during fog events, significant evapotranspiration may occur. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Multi‐depth monitoring of electrical conductivity and temperature of groundwater at a multilayered coastal aquifer: Jeju Island,Korea     

Kue‐Young Kim  Chul‐Min Chon  Ki‐Hwa Park  Yun‐Seok Park  Nam‐Chil Woo 《水文研究》2008,22(18):3724-3733

To supplement conventional geophysical log data, this study presents temporal variations in electrical conductivity (EC) and temperature with depth in a multilayered coastal aquifer, on the eastern part of Jeju Island, Korea. One‐month time‐series data obtained at eight points from a multi‐depth monitoring system showed that semidiurnal and semimonthly tidal variations induced dynamic fluctuations in EC and temperature. At some depths, EC ranged from 1483 to 26 822 µS cm^?1, while some points showed no significant variations. The results of EC log and time‐series data revealed that a sharp fresh‐saltwater interface occurred at low tide, but the diffusion zone broadened to 20 m at high tide. EC, temperature, and tide level data were used for the cross‐correlation analysis. The response time of EC and temperature to tide appears to range from less than 30 min to 11 h. Using end‐member mixing analysis (EMMA), the fraction of variations of chloride concentration in the multilayered aquifer was explained, and a conceptual model was developed which subdivided the coastal aquifer into four vertical zones. The percentage of water derived from seawater varied from 2 to 48 at specific depth, owing to tidal fluctuations. Continuous observations of EC and temperature at multiple depths are powerful tools for quantifying the transport of saline water by tidal variations in multilayered coastal aquifers. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Hydrological effects of climate change,groundwater withdrawal,and land use in a small Korean watershed     

Kil Seong Lee  Eun‐Sung Chung 《水文研究》2007,21(22):3046-3056

The effects of variability in climate and watershed (groundwater withdrawal and land use) on dry‐weather streamflows were investigated using SWAT (Soil and Water Assessment Tool). The equation to predict the total runoff (TR) using climate data was derived from simulation results for 30 years by multiple regression analysis. These may be used to estimate effects of various climate variations (precipitation during the dry period, precipitation during the previous wet period, solar radiation, and maximum temperature). For example, if daily average maximum temperature increases by 3 °C, TR during the dry period will decrease by 27·9%. Similarly, groundwater withdrawals strongly affect streamflow during the dry period. However, land use changes (increasing urbanization) within the forested watershed do not appear to significantly affect TR during the dry period. Finally, a combined equation was derived that describes the relationships between the TR during the dry period and the climate, groundwater withdrawal and urban area proportion in a small monsoon watershed. This equation will be effective to predict the water availability during the dry periods in the future since it is closely related to changes of temperature, precipitation, solar radiation, urban area ratio, and groundwater withdrawal quantity. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献