珠江三角洲思贤滘水文泥沙特征和现代演变     

郑德延  温孝胜  赵焕庭  宋朝景 《热带海洋学报》1992,(1)

根据思贤滘的水文泥沙、地形和底质资料,分析了思贤滘的河床底质类型、分布规律、沉积物粒度组成、重矿物含量以及河床演变特征等,讨论了思贤滘的泥沙运移特点,指出西江和北江的推移质均已进入思贤滘,但未通过,因此,对思贤滘凹岸堤围的险段岁修工程不容忽视;并对思贤滘的整治规划提出了不设闸的刍议。  相似文献   

The Western Boundary of the Equatorial Pacific Upwelling: Some Consequences of Climatic Variability on Hydrological and Planktonic Properties     

Martine Rodier  Gérard Eldin  Robert Le Borgne 《Journal of Oceanography》2000,56(4):463-471

The longitude of the western limit of the equatorial Pacific upwelling is a key parameter for studies of carbon budget and pelagic fisheries variability. Although it is well defined at the surface on the equator by a salinity front and a sharp variation of the partial pressure of CO₂, data from two equatorial cruises make it clear that this hydrological limit does not necessarily coincide with the boundary of the nitrate and chlorophyll enriched area. In January-February 1991 during a non-El Niño period, when trade winds and the South Equatorial current (SEC) were favorable to upwelling, the two limits were at the same longitude. Conversely, in September-October 1994 during El Niño conditions, when the equatorial upwelling had stopped, the nitrate and chlorophyll enriched zone was found a few degrees of longitude east of the hydrological boundary (5.5° at the surface and 2.5° for the 50 m upper layer), whereas no such offset was observed for zooplankton biomass. A simple model, based on the HNLC (High Nutrient - Low Chlorophyll) ecosystem functioning, was initialized with nitrate uptake measurements and estimates of upwelling break duration. The model results support the hypothesis that zonal separation of the limits arises from biological processes (i.e. nitrate uptake and phytoplankton grazing) achieved during that upwelling break.  相似文献   

Dependence of thermal conductivity of snow on microstructure     

P. K. Satyawali  A. K. Singh 《Journal of Earth System Science》2008,117(4):465-475

A geometrical model, including different geometrical shapes influencing thermal conductivity of snow is proposed. The geometrical model has been assumed to comprise of unit cells having solid (ice) inclusion as an aggregation of spherical, cylindrical or cubical shapes with vertical connection, arranged in a cubic packing. From the geometrical model and one-dimensional heat transfer theory, the effective thermal conductivity has been computed. For this purpose, coupled one-dimensional heat transfer equations have been solved for steady-state condition to account for conduction in ice, conduction in air and latent heat transfer due to water vapour sublimation through air. The model demonstrates the dependency of thermal conductivity on density, grain-spacing, grain contact ratio and temperature. Spherical inclusions give highest conductivity while cubical inclusion estimates lowest value for the same density. Thermal conductivity has been found increasing sharply near to the packing density for all three shapes. Empirical model results and results obtained from existing microstructure based models have also been compared with the present model.  相似文献   

Surface energy balance of seasonal snow cover for snow-melt estimation in N-W Himalaya   总被引：2，自引：0，他引：2  

Prem Datt  P. K. Srivastava  P. S. Negi  P. K. Satyawali 《Journal of Earth System Science》2008,117(5):567-573

This study describes time series analysis of snow-melt, radiation data and energy balance for a seasonal snow cover at Dhundi field station of SASE, which lies in Pir Panjal range of the N-W Himalaya, for a winter season from 13 January to 12 April 2005. The analysis shows that mean snow surface temperature remains very close to the melting temperature of snow. It was found close to −1°C for the complete observational period which makes the snow pack at Dhundi moist from its beginning. The average air temperature over this period was found to be 3.5°C with hourly average variation from −5.5°C to 13°C. The snow surface at this station received a mean short wave radiation of 430W m⁻², out of which 298W m⁻² was reflected back by the snow surface with mean albedo value of 0.70. The high average temperature and more absorption of solar radiation resulted in higher thermal state of the snowpack which was further responsible for faster and higher densification of the snowpack. Net radiation energy was the major component of surface energy budget with a mean value of 83W m⁻². Bulk transfer model was used to calculate turbulent fluxes. The net energy was utilized for satisfying cold content and snow-melt by using measured snow surface temperature and density of snow pack. The mean square error between calculated and measured daily snow-melt was found to be approximately 6.6mm of water equivalent.  相似文献   

陆面水文—气候耦合模拟研究进展     

占车生  宁理科  邹靖  韩建 《地理学报》2018,73(5):893-905

陆面水文过程是全球/区域气候模式十分重要而又十分薄弱的环节。本文通过科学文献计量法,分析了陆面水文—气候耦合研究的发展状况及研究热点和趋势,并进一步对研究中存在的问题和挑战进行综述和探讨。现有多数气候模式中的陆面模式主要基于一维垂向结构设计,缺乏对流域尺度水文过程的精细描述,尤其缺乏下垫面人类活动影响的描述。因此,为了科学认识水文过程与气候变化的相互反馈作用机制,大量研究主要通过耦合流域水文模型与气候模式,研究不同时空尺度下水文过程变化的气候反馈效应。陆面过程模式中水文过程的改进和大尺度水文模型发展为陆面水文—气候耦合模拟奠定基础,在此基础上,陆面水文—气候耦合研究正从传统的单向耦合研究逐步发展为考虑气候—水文反馈的双向耦合研究。然而,双向耦合研究远未成熟,其问题集中表现为陆面水文—气候模型耦合过程如何匹配并提高系统稳定性、研制有效的尺度转换方案、完善参数化方案并评估参数不确定性、研制有效参数移植方法并提高模型适用性以及高分辨率甚至超分辨率模拟等方面,逐步解决上述问题并提高模拟精度是未来水文—气候耦合模拟研究的重要发展方向。  相似文献   

Groundwater Recharge and Mixing in Arid and Semiarid Regions: Heihe River Basin, Northwest China     

CAO Guoliang  ZHENG Chunmiao  Craig T. SIMMONS 《《地质学报》英文版》2016,90(3):971-987

A sound understanding of groundwater recharged from various sources occurring at different time scales is crucial for water management in arid and semi-arid river basins. Groundwater recharge sources and their geochemical evolution are investigated for the Heihe River Basin(HRB) in northwest China on the basis of a comprehensive compilation of geochemical and isotopic data. Geochemical massbalance modeling indicates that mountain-block recharge accounts for a small fraction(generally less than 5%) of the shallow and deep groundwater sustaining the oasis, whereas infiltration of rivers and irrigation water contribute most of the groundwater recharge. Dedolomitization is the primary process responsible for the changes in groundwater chemical and carbon isotope compositions from the piedmont to the groundwater discharge zone, where the dedolomitization is very likely enhanced by modern agricultural activities affecting the shallow groundwater quality. Analysis of radioactive isotopes suggests that these primary recharge sources occur at two different time scales. Radiocarbon-derived groundwater age profiles indicate a recharge rate of approximately 12 mm/year, which probably occurred during 2000–7000 years B.P., corresponding to the mid-Holocene humid period. The recharge of young groundwater on the tritium-dated time scale is much higher, about 360 mm/year in the oasis region. Infiltration from irrigation canals and irrigation return flow are the primary contributors to the increased young groundwater recharge. This study suggests that groundwater chemistry in the HRB has been influenced by the complex interaction between natural and human-induced geochemical processes and that anthropogenic effects have played a more significant role in terms of both groundwater quantity and quality.  相似文献   

气候变化对水文水资源影响评价的不确定性分析   总被引：8，自引：1，他引：8  

郭生练  曾光明 《水文》1995,(6):1-5

在评价气候变化对水文水资源影响的各个环节中都存在不确定性。以蓝塘和花园两流域为例，应用ＭｏｎｔｅＣａｒｌＯ和非参数方法研究区域水文评价模型参数和径流的不确定性估计。结果表明：径流对降水的变化要比对气温升高敏感；径流系数较小的流域，其变化幅度反而大。若考虑信度水平为５％的不确定度和最不利的气候情景组合，蓝塘和花园两流域的洪峰流量将分别增大４５．２１％和４９．２７％，这将对防洪工程造成重大和不利的影响。  相似文献   

太白山末次冰期冰碛物微结构和微构造研究     

唐永仪 《冰川冻土》1990,12(3):235-241

  相似文献   

都市化对小流域水文影响的研究   总被引：3，自引：0，他引：3       下载免费PDF全文

吴学鹏  林俊俸 《水科学进展》1992,3(2):155-160

综述了受都市化影响的小流域水文特征和研究途径.通过实际观测和概化模型试验,提出了反映都市化水文效应的指标,即当不透水面积比超过20%时,都市化影响表现明显.最后介绍了都市化影响的小流域雨洪计算方法.  相似文献   

碳酸—硫酸盐岩建造岩溶水化学场模型和溶蚀量评价理论初探     

曹玉清  胡宽瑢 《吉林大学学报(地球科学版)》1988,(1)

本文讨论了在完整岩溶泉域内,从灰岩裸露的补给区,至灰岩隐伏于地下的径流区宜至深埋区,可溶岩矿物与水相互作用所发生的不同化学作用和分带性;以及不同化学作用下限确定原则和方法;岩溶水化学类型随深度变化规律;可溶岩矿物溶蚀(解)量的方法。  相似文献