Analytical investigation of the exact groundwater divide between rivers beyond the Dupuit–Forchheimer approximation     

Ruoyi Li  Xu-Sheng Wang 《水文研究》2021,35(2):e14036

The groundwater divide is a key feature of river basins and significantly influenced by subsurface hydrological processes. For an unconfined aquifer between two parallel rivers or ditches, it has long been defined as the top of the water table based on the Dupuit–Forchheimer approximation. However, the exact groundwater divide is subject to the interface between two local flow systems transporting groundwater to rivers from the infiltration recharge. This study contributes a new analytical model for two-dimensional groundwater flow between rivers of different water levels. The flownet is delineated in the model to identify groundwater flow systems and the exact groundwater divide. Formulas with two dimensionless parameters are derived to determine the distributed hydraulic head, the top of the water table and the groundwater divide. The locations of the groundwater divide and the top of the water table are not the same. The distance between them in horizontal can reach up to 8.9% of the distance between rivers. Numerical verifications indicate that simplifications in the analytical model do not significantly cause misestimates in the location of the groundwater divide. In contrast, the Dupuit–Forchheimer approximation yields an incorrect water table shape. The new analytical model is applied to investigate groundwater divides in the Loess Plateau, China, with a Monte Carlo simulation process taking into account the uncertainties in the parameters.  相似文献   

Effect of Caliche Nodules on Soil Water Storage in the Northern Loess Plateau of China     

Tiexiong Gong  Yuanjun Zhu  Yunqiang Wang  Wei Hu  Ming'an Shao 《洁净——土壤、空气、水》2019,47(7)

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塔里木盆地南缘8.5 ka以来的黄土岩石磁学特征及其磁化率变化机制          下载免费PDF全文

吕爽  韩文霞  张涛  韩凤清  卢胜城  马学海  张志高 《地球物理学报》2019,62(8):3053-3066

黄土岩石磁学参数是古气候研究中的重要指标，其中磁化率应用最为广泛，并在黄土高原地区取得重大进展，其受控于成壤作用的变化机制也被普遍接受.然而在黄土高原外缘的新疆地区，磁化率的变化机制仍不明确，导致磁化率的古气候意义在该区存在较大争议.本文选取塔里木盆地南缘具有精确年代控制的典型黄土剖面（羊场剖面）开展岩石磁学和高分辨率磁化率研究，利用交叉小波分析方法并结合剖面粒度、矿物及元素特征对该地区磁化率变化机制进行初步探讨.结果显示，羊场剖面的岩石磁学性质主要由粗颗粒软磁性矿物所控制，同时也表现出一定的顺磁性特征.根据载磁矿物和磁化率变化特征可将剖面进一步划分为两个阶段：阶段Ⅰ（8.5~2.5 ka），载磁矿物以亚铁磁性的磁铁矿为主，磁化率值整体较高；阶段Ⅱ（2.5~0.2 ka），亚铁磁性矿物依然占据主导地位，但硬磁性矿物和以黄铁矿为代表的顺磁性矿物相对增多，磁化率值显著降低.相关性研究和交叉小波分析表明：阶段Ⅰ磁化率与粗颗粒组分的变化具有一致性，符合"风速论"模式；阶段Ⅱ磁化率不仅与粗颗粒组分具有明显的正相关关系，而且与指示成壤作用强度的频率磁化率百分含量呈现出显著的负相关关系，暗示了阶段Ⅱ的磁化率变化可能受到"风速论"和"还原性成壤"模式的共同影响.本文拓宽了对新疆地区黄土岩石磁学特征及其磁化率变化机制的深入理解，也为利用磁化率恢复新疆及中亚地区全新世以来的古气候变化历史提供了新的线索.  相似文献   

黄土高原沟谷地貌发育演化研究进展与展望     

熊礼阳  汤国安 《地球信息科学学报》2020,22(4):816-826

黄土沟谷是黄土地貌中最有活力、最具变化、最富特色的对象单元,黄土高原千沟万壑的地貌形态以及触目惊心的侵蚀状态也让区域内沟谷地貌的形成、发育及演化问题成为研究中焦点及前沿性科学问题。近年来,诸多学者采用地学测年法、特征表达法、监测模拟法力图实现对黄土沟谷发育演化进程中“过去-现代-未来”的科学认知。这些研究在相当程度上丰富了黄土沟谷发育过程的认知。本文梳理了黄土高原沟谷地貌演化相关研究的现状,并从黄土高原地貌演化、黄土沟谷发育、基于DEM的沟谷信息提取与表达等研究进行了系统的回顾、梳理与分析。此外,本文提出“黄土沟道剖面群组”概念与方法,试图从新的视角审视黄土沟谷地貌发育演化过程。沟道剖面在黄土沟谷发育演化进程中传递物质能量和累积地形动力,并通过径流节点的串联实现剖面群的连接与组合,形成独特的剖面“群组”模式;该沟道剖面群组是集黄土沟谷地貌特征与过程于一体的综合信息集成体,其三维空间结构是对黄土沟谷地貌发育演化的高度抽象与映射,并可望进一步丰富黄土高原数字地形分析理论与方法体系,为黄土高原黄土地貌成因机理与空间分异格局带来创新的认识。  相似文献   

1980—2016年黄土高原地区人口和可达性异速标度分析     

吕敏娟  曹小曙 《地理科学进展》2020,39(11):1884-1897

论文基于黄土高原地区乡镇1980、1990、2000、2010、2016年5期截面数据,利用位序—规模法则和异速标度律,分析了乡镇尺度人口和可达性规模结构、等级体系及异速标度演化关系。结果表明：① 人口规模以中小等级乡镇为主,60%的乡镇人口规模正增长,总体呈“南北高、中间低”分布格局;可达性水平总体呈明显上升趋势,空间上自东南向西北逐渐降低;河谷平原区人口规模和可达性均最大。② 人口和可达性均呈位次型分布,人口位序—规模具有明显双分形结构,由均衡向极化转变;可达性位序—规模以2000年为转折点由双分形演变为单分形,由低水平均衡转向更高水平均衡。③ 3006个乡镇整体以正异速生长为主,负异速生长为辅,黄土高塬沟壑区、河谷平原区内乡镇异速生长类型以人口增长正异速生长为主,黄土丘陵沟壑区、土石山区、沙地和沙漠区内乡镇以人口下降正异速生长为主,农灌区内乡镇异速生长以人口增长正异速一级和人口下降负异速一级为主。最后根据人口和可达性异速类型和空间分布特征,提出各分区发展的建议。  相似文献   

Analysis of nonstationarity in low flow in the Loess Plateau of China          下载免费PDF全文

Kun‐xia Yu  Lars Gottschalk  Xiang Zhang  Peng Li  Zhanbin Li  Lihua Xiong  Qian Sun 《水文研究》2018,32(12):1844-1857

An approach for nonstationary low‐flow frequency analysis is developed and demonstrated on a dataset from the rivers on the Loess Plateau of China. Nonstationary low‐flow frequency analysis has drawn significant attention in recent years by establishing relationships between low‐flow series and explanatory variables series, but few studies have tested whether the time‐varying moments of low flow can be fully described by the time‐varying moments of the explanatory variables. In this research, the low‐flow distributions are analytically derived from the 2 basic explanatory variables—the recession duration and the recession coefficient—with the assumption that the recession duration and recession coefficient variables follow exponential and gamma distributions, respectively; the derived low‐flow distributions are applied to test whether the time‐varying moments of explanatory variables can explain the nonstationarities found in the low‐flow variable. The effects of ecosystem construction measures, that is, check dam, terrace, forest, and grassland, on the recession duration and recession coefficient are further discussed. Daily flow series from 11 hydrological stations from the Loess Plateau are used and processed with a moving average technique. Low‐flow data are extracted following the pit under threshold approach. Six of the 11 low‐flow series show significant nonstationarities at the 5% significance level, and the trend curves of the moments of low flow are in close agreement with the curves estimated from the derived distribution with time‐dependent moments of the recession duration and time‐constant moments of the recession coefficient. It is indicated that the nonstationarity in the low‐flow distribution results from the nonstationarity in the recession duration in all 6 cases, and the increase in the recession duration is resulted from large‐scale ecosystem constructions rather than climate change. The large‐scale ecosystem constructions are found to have more influence on the decrease in streamflow than on the increase in watershed storage, thus resulting in the reduction of low flow. A high return period for the initial fixed design value decreases dramatically with an increasing recession duration.  相似文献   

Application of Glycerol Dialkyl Glycerol Tetraether Lipids in Paleoenvironment Reconstruction of Loess Deposits: A Review of Recent Progresses     

Shaohua Tian  Guoqiao Xiao  Huan Yang 《地球科学进展》2020,35(5):465-477

The Glycerol Dialkyl Glycerol Tetraethers (GDGTs) occur ubiquitously in a wide range of environments, such as loess, peat, lake, soil, and ocean, which vary compositionally in response to environmental changes, and provide a series of biomarker proxies for paleoenvironmental reconstruction. This paper introduced the structures and biological sources of GDGTs, and reviewed the recent progresses of the application of the GDGTs proxies in the paleoenvironmental reconstruction of loess deposits. The main progresses include: \mathrm{①} The GDGTs proxies have been widely used in reconstructing the climate changes in loess deposits, and have established the temperature changes of last 800 ka for the Chinese Loess Plateau; \mathrm{②}Temperature variations in Chinese Loess Plateau displayed significant correlation with the Northern Hemisphere insolation, which may be also regulated by the surface vegetation conditions; and \mathrm{③} In the Chinese Loess Plateau, the increase in monsoon precipitation during the last deglaciation significantly lagged behind the rise of temperature. However, problems still exist in the current studies. For instance, the GDGTs-based temperature is likely overestimated, probably reflecting the temperature of warm season, and relationships between GDGT indices and climate factors are still unclear. In the future, the development of new proxies and more accurate regional calibrations based on the separation of 6- methyl GDGTs are expected to provide more reliable paleoenvironmental information, and will provide essential evidence for the evolution of hydrothermal pattern and mechanisms behind climate changes in different regions.  相似文献   

Variation in the sediment deposition behind check‐dams under different soil erosion conditions on the Loess Plateau,China          下载免费PDF全文

Yanhong Wei  Zhong He  Juying Jiao  Yujin Li  Yixian Chen  Hengkang Zhao 《地球表面变化过程与地形》2018,43(9):1899-1912

To maintain a reasonable sediment regulation system in the middle reaches of the Yellow River, it is critical to determine the variation in sediment deposition behind check‐dams for different soil erosion conditions. Sediment samples were collected by using a drilling machine in the Fangta watershed of the loess hilly–gully region and the Manhonggou watershed of the weathered sandstone hilly–gully (pisha) region. On the basis of the check‐dam capacity curves, the soil bulk densities and the couplet thickness in these two small watersheds, the sediment yields were deduced at the watershed scale. The annual average sediment deposition rate in the Manhonggou watershed (702.0 mm/(km²·a)) from 1976 to 2009 was much higher than that in the Fangta watershed (171.6 mm/(km²·a)) from 1975 to 2013. The soil particle size distributions in these two small watersheds were generally centred on the silt and sand fractions, which were 42.4% and 50.7% in the Fangta watershed and 60.6% and 32.9% in the Manhonggou watershed, respectively. The annual sediment deposition yield exhibited a decreasing trend; the transition years were 1991 in the Fangta watershed and 1996 in the Manhonggou watershed (P < 0.05). In contrast, the annual average sediment deposition yield was much higher in the Manhonggou watershed (14011.1 t/(km²·a)) than in the Fangta watershed (3149.6 t/(km²·a)). In addition, the rainfalls that induced sediment deposition at the check‐dams were greater than 30 mm in the Fangta watershed and 20 mm in the Manhonggou watershed. The rainfall was not the main reason for the difference in the sediment yield between the two small watersheds. The conversion of farmland to forestland or grassland was the main reason for the decrease in the soil erosion in the Fangta watershed, while the weathered sandstone and bare land were the main factors driving the high sediment yield in the Manhonggou watershed. Knowledge of the sediment deposition process of check‐dams and the variation in the catchment sediment yield under different soil erosion conditions can serve as a basis for the implementation of improved soil erosion and sediment control strategies, particularly in semi‐arid hilly–gully regions. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

皋兰老虎台红砂种群在不同坡向的空间格局及关联性          下载免费PDF全文

刘旻霞  南笑宁  夏素娟  李全弟  蒋晓轩 《干旱区地理》2019,42(6):1359-1367

种群的空间格局是研究植物种群相互作用及种群与环境关系的重要方法。红砂（Reaumuria soongarica）是黄土高原半干旱区的主要物种，通过野外的群落调查，运用空间点格局分析法中的Ripley K函数，分析甘肃皋兰老虎台荒漠植被不同坡向红砂种群的空间分布格局与种内关联。结果显示：红砂种群为增长型种群，其在不同坡向的分布具有显著差异；南坡及西南坡坡向上，红砂种群Ⅰ、Ⅱ级个体在小尺度上呈显著聚集分布，随着龄级及空间尺度的增加，红砂种群聚集强度逐渐减弱，最后趋于随机分布。西坡、西北坡坡向上生长大量的蓍状亚菊（Ajania achilloides）和短花针茅（Stipa breviflora）等对红砂的生长造成抑制并加剧种间竞争，各级红砂种群的分布格局均以随机分布为主。不同坡向上，红砂种群Ⅰ、Ⅱ龄级个体之间在小尺度内表现为负关联，随着尺度增加关联度降低，Ⅲ、Ⅳ龄级与Ⅰ、Ⅱ龄级个体之间呈显著的负关联，而Ⅲ、Ⅳ龄级之间没有明显关联性，表明龄级相近的个体在空间分布上是相互独立的。综上所述，在黄土高原半干旱区，影响红砂种群分布的主要因素除了其自身的生物、生态学特性外，微生境的影响也十分重要。  相似文献   

新疆及中亚地区斜坡灾害研究现状与展望     

伊学涛  尚彦军  李守定  崔振东  孟和  曹小红 《新疆地质》2021,(1):156-161

新疆和中亚五国山河相连,都是“一带一路”建设的重要支点,但也是滑坡、泥石流等斜坡灾害的高发区,且两地的地质灾害发育有着明显的共性。本文对新疆和中亚地区的斜坡灾害研究现状进行综述,分析了两地斜坡灾害形成机理、发育规律,即中高山地分布集中,受降雨和冰雪融水影响很大,黄土滑坡发育。新疆的斜坡灾害研究多围绕公路、水利等工程设施;中亚地区的斜坡灾害研究以自然灾害居多,且在很大程度上受地震作用控制。最后,分析了新疆及中亚地区斜坡灾害研究的发展趋势,建议建立现代化的灾害监测预警系统,加强“一带一路”沿线国家地质灾害研究的国际合作。  相似文献