Late Holocene upper bounds of flood magnitudes and twentieth century large floods in the ungauged, hyperarid alluvial Nahal Arava, Israel   总被引：1，自引：0，他引：1  

Yael Jacoby  Tamir Grodek  Yehouda Enzel  Naomi Porat  Eric V. McDonald  Ofer Dahan   《Geomorphology》2008,95(3-4):274-294

The impact of large twentieth century floods on the riparian vegetation and channel morphology of the relatively wide anabranching and braided Nahal Arava, southern Israel, was documented as part of developing tools to (a) identify recent large floods, (b) determine these flood's respective magnitudes in alluvial ungauged streams, and (c) determine long-term upper bounds to flood stages and magnitudes. Along most of its course Nahal Paran, a major tributary that impacts the morphology, floods and sediments of Nahal Arava at the study reach, is a coarse-gravel, braided ephemeral stream. Downstream of the Arava–Paran confluence, aeolian and fluvial sand delivered from eastern Arava valley alters the channel morphology. The sand has accreted up to 2.5 m above the distinct current channels, facilitating the recording of large floods. This sand enhances the establishment of denser riparian vegetation (mainly Tamarix nilotica and Haloxylon persicum) that interacts with floods and affects stream morphology. A temporal association was found between specific floods recorded upstream and tree-ring ages of re-growth of flood-damaged tamarix trees (‘Sigafoos trees’) in the past 30 years. This association can be utilized for developing a twentieth century flood chronology in hyperarid ungauged basins in the region. The minimum magnitude of the largest flood that covered the entire channel width, estimated from flood deposits, is approximately 1700–1800 m³s^− 1. This is a larger magnitude than the largest gauged flood of 1150 m³s^− 1 that occurred in 1970 about 30 km upstream in Nahal Paran. Our estimation agrees with flood magnitude estimated from the regional envelope curve of the largest floods. Based on Holocene alluvial stratigraphy and OSL dating in the study reach we also conclude that flood stages did not reach the late Holocene ( 2.2 ka) surface and therefore we estimate a non-exceedance upper bound of  2000 m³s^− 1 flood magnitudes for Nahal Arava during that interval. This study indicates that in unfavorable areas the combination of hydrology, fluvial morphology and botanic evidence can increase our understanding of ungauged basins and give information crucial for hydrology planning.  相似文献   

基于不同时间尺度的非结冰期水面蒸发影响因素灰色关联分析     

魏光辉  陈亮亮  杨鹏年 《沙漠与绿洲气象(新疆气象)》2013,(4)

根据新疆尉犁县气象站2008年4-10月非结冰期水面蒸发量及相关常规气象观测资料,利用灰色关联分析法研究了不同时间尺度下各气象要素对水面蒸发量的影响程度。结果表明：在不同计算尺度下,水汽压、相对湿度与日照时数这三气象因素的影响程度排序无变化,说明计算尺度对其影响较小;温度（包括平均气温、最高气温与最低气温）与风速因素对蒸发量的影响程度随着研究尺度的变化而变化,其中平均温度与平均风速这两因素随着研究尺度的增大而影响程度随之增大;构成研究区域水面蒸发主要影响因素的是温度因素（包括平均气温、最高气温与最低气温）与风速因素。研究结果为区域水资源的规划、优化调度与管理提供了重要参考。  相似文献   

甘肃第四纪古地理环境   总被引：5，自引：2，他引：5  

曹兴山 《甘肃地质》1996,5(2):40-56

第四纪在全球性冰期和间冰期气候影响下，甘肃气候呈干旱、寒冷与温暖、湿润交替变化。沉积物以灰色格调为主，水平和垂直分带规律明显，成因类型复杂。各地区在小气候影响下植被发育不平衡。总的看来，以干旱区系草本植物为主，喜温暖湿热的木本植物较少，一般呈荒漠草原型和疏林草原型，局部为森林草原型。动物群的分布和古人类的发展受古地理环境影响：早更新世早期以大型哺乳动物为主；早更新世晚期和中更新世以穴居的鼠兔类为主；晚更新世以干旱—半干旱草原型动物群为特征；全新世在适宜条件下人类文化得到发展，部分野生动物在人类豢养下成为家畜  相似文献   

Environmental isotopic and hydrochemical study of groundwater in the Ejina Basin,northwest China   总被引：5，自引：0，他引：5  

Y. H. Su  G. F. Zhu  Q. Feng  Z. Z. Li  F. P. Zhang 《Environmental Geology》2009,58(3):601-614

The study investigates the groundwater evolution and its residence time in the Ejina Basin, northwest China according to isotope and hydrochemical analyses results. The groundwater chemistry is mainly controlled by the dissolution of halite, Glauber’s salt, gypsum, dolomite and calcite, also influenced by other processes such as evaporation, ion exchange, and deposition. Based on tritium content in atmospheric precipitation and by adopting a model with exponential time distribution function, the mean residence time of the unconfined aquifer groundwater with fairly high tritium activities (21–49 TU) is evaluated. The results show that these groundwaters have low residence time (5–120 years) and are renewable. In contrast, the deep confined groundwaters are tritium-free and radiocarbon values range from 18.3 to 26.7 pmc. According to the most commonly used ¹⁴C correction models, the radiocarbon groundwater ages were calculated which yield ages of approximately 4,087–9,364 years BP. Isotopic signatures indicate formation of deep confined groundwaters in a colder and wetter climate during the late Pleistocene and Holocene. It is suggested that long-term, rational water usage guide should be set up for the Heihe River Basin as a whole to permit a considerable discharge to the Ejina Basin.  相似文献   

准噶尔盆地浅覆盖区浅钻化探找矿方法探索     

肖艳东  孟贵祥  范侥  赵玉京  王君良 《新疆地质》2019,(1):40-43

通过拉伊克勒克典型浅覆盖区浅钻化探成果,介绍了浅钻化探工作方法和取得的试验研究成果,显示该方法有效,经济可行,效率较高,操作简便,充分证明了浅钻化探技术在准噶尔干旱荒漠浅覆盖区是有效的找矿手段。  相似文献   

亚洲中部干旱半干旱区近100年来的气温变化研究   总被引：8，自引：3，他引：5  

王劲松  陈发虎  张强  靳立亚  李静  金明  陈建徽 《高原气象》2008,27(5)

利用亚洲中部干旱半干旱区1961—2003年共计69个站的气温实测资料,并通过EOF展开的延长插补方法,将研究区的气温序列延长到1901年,进而分析了这一区域近100年来的气温变化。研究表明,该区域气温的一致性变化占主导地位,同时存在东部季风区、中亚、蒙古高原和塔里木干旱区等4个主要温度变化分区,均表现出显著的增暖趋势,其代表站近100年来线性拟合的增温率分别为0.19,0.16,0.23和0.15℃/10a,研究区平均增温率为0.18℃/10a,冬季达0.21℃/10a,远高于北半球、全球和我国的增温率,但与青藏高原增温率相近。除20世纪10年代和50年代外,研究区气温变化主要取决于冬季温度的变化。研究区近100年来的气温变化经历了70年代以前的相对缓慢升温和以后的显著升温过程,且增温率越来越大。亚洲中部干旱半干旱区的气温变化过程与我国东部地区显著不同,没有出现明显的20~40年代暖期,整个升温过程由6次明显的锯齿状的升温-降温变化过程(即20,40,60,80,90年代和本世纪初气温变化过程)构成,升温阶段持续时间较长,幅度较大,而降温阶段时间短,幅度小,但不论升温还是降温过程,其变化幅度均大于我国东部和全球平均。  相似文献   

Sediment transport for desert watersheds in erodible materials     

Ran Gerson 《地球表面变化过程与地形》1977,2(4):343-361

Sediment transport for five small watersheds in arid southern Israel, eroded into shales, chalks, anhydrites and alluvium is studied. Analysis includes data from three large watersheds in the southern United States. Results indicate that floodwater heavily laden with suspended load (10-60 per cent, by weight) is characteristic of watersheds cut in erodible materials. No correlation was found between environmental characteristics such as lithology, catchment area, angle of slope or rainfall intensity and suspended-sediment concentration or texture. The carrying capacity for sands, derived both from hillslopes and channel alluvium is greatly increased by high suspended silt concentration, the trend being (where R = ratio, % fines/% sand; C_s = suspended load concentration, per cent by weight). The high concentration of fine sediment effectively causes more sand transport than would normally occur. This is also true for transport of coarser clastics; higher velocities, typical of highly concentrated silt suspensions, increased competence for transporting pebbles and boulders. The action of a large variety of processes (splash, wash, rilling, gullying, sliding, mudflow) combine with low infiltration and high credibility to render every rainstorm erosionally effective, and high concentrations of washload increase both the capacity and competence of coarse clastic transport. Whole basins are thus subjected to high rates of denudation (2-10 mm/yr).  相似文献   

中国西部干旱地区太阳直接辐射通量密度与大气质量的关系   总被引：1，自引：0，他引：1  

王尧奇  韦志刚 《高原气象》1990,9(3):327-336

本文根据中国西部干旱地区大气物理状态(大气可降水量和大气浑浊度)的变化范围,利用太阳直接辐射通量密度的理论计算公式,计算了各种大气透明系数状况下的太阳直接辐射通量密度。计算结果表明,大气质量m=2时的透明系数P_2和m相同时,由于水汽和气溶胶的含量配置不同而引起太阳直接辐射通量密度的差异,在辐射日变程的主要时段(m=1-3)内并不大。于是得到各种透明系数P_2状况下太阳直接辐射通量密度随大气质量变化的平均关系。不同海拔高度比较,当透明系数P_2相同时,各自的大气物理状态虽然不同,但m相同时的太阳直接辐射通量密度基本相同。现有的表征太阳直接辐射通量密度值和大气质量联系的关系式都不能很好地描述计算结果。根据太阳直接辐射通量密度随大气质量变化的特性,我们提出了新的关系式。最后,整理了不同拔海高度和不同地理景观的四个日射站(西藏那曲、青海格尔木、甘肃敦煌和民勤)的多年观测资料。经验计算结果与观测值比较,一致性良好。  相似文献   

Metals content in sediments of ephemeral streams with small reservoirs(the Negev Desert)     

《国际泥沙研究》2020,35(3):269-277

The content of 19 metals(chromium,cobalt,nickel,strontium,arsenic,magnesium,barium,cesium,gallium,rubidium,uranium,vanadium,zinc,lead,copper,cadmium,iron,manganese,and aluminum) in sediment in three ephemeral streams(Nahal Sansana,Nahal Revivim and Nahal Pura) with reservoirs in the Negev Desert is studied herein.The study was done in September 2016.The samples were collected from the surface layer of sediment(up to 10 cm) in the reservoirs and in the channels upstream and downstream of the reservoirs.Silt,which on average,accounted for 72% dominated in the sediment.In the spatial distribution of the particle size,sand and gravel fractions were deposited in the reservoirs.Aluminum,iron,and magnesium accounted for 99% of all analyzed metals.The Principal Component Analysis(PCA) and Hierarchical Cluster Analysis(HCA) showed that sediment in the Negev Desert channel upstream of the reservoirs had similar concentrations of metals.Similarities were also found between the analyzed reservoirs.The bottom sediment in reservoirs had higher concentrations of metals than sediment upstream and downstream of the reservoirs.The comparison of concentrations in upstream and downstream locations did not show any unambiguous trends because metal concentrations downstream from the reservoirs were not always lower than upstream of the reservoirs.The analysis of the sediment enrichment factor(EF) showed the highest value in the reservoirs and the lowest downstream of the reservoirs.The concentrations of most analyzed metals did not indicate the possibility of potential ecological risk(SQG).  相似文献   

Determination of groundwater availability in shallow arid region aquifers utilizing GIS technology: a case study in Hada Al-Sham, Western Saudi Arabia     

A. S. El-Hames  K. A. Al-Ahmed 《Hydrogeology Journal》2005,13(4):649-648

A simple, physically based method is developed in this paper to assist in the allocation of areas with high groundwater potential and for the determination of maximum allowed pumping rate to ensure proper groundwater management. This method utilizes the aquifer physical properties as well as GIS technology to accomplish this purpose. The design of this method was considered to be applicable in areas with little data, such as in most arid regions. This technique was applied to a catchment in an arid environment where qualitative as well as quantitative analyses of the results were undertaken. Locations of available groundwater and rates of maximum allowable pumping were compared with observations and experiments in the field and a good agreement was found. It was concluded that the best groundwater location was in the alluvial area, which represents only 16% of the total aquifer, which is a typical case in arid region catchments. The rate of maximum pumping was estimated to be 65 m³/h. However, to benefit 55% of the area, the maximum pumping rate should only be 40 m³/h with an average rate throughout the area (55%) of about 24 m³/h.This revised version was published online in December 2004 with corrections to the category.  相似文献