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   

An improved analytical approach for simulating the lateral kinematic distress of deepwater offshore pipelines     

《Applied Ocean Research》2019

Offshore pipelines are critical infrastructures and any possible damage may have devastating financial and environmental consequences. Earthquake-related geohazards (such as strong ground motion, active seismic faults, submarine landslides and debris flows) consist crucial threats that an offshore pipeline has to overcome. The main aim of the current study is to examine analytically a seabed-laid offshore pipeline subjected to a lateral kinematic distress due to a submarine landslide or a debris flow. Extra emphasis is given on the impact of pipe-soil interaction on the pipe response, by the realistic representation of the soil resistance via a tri-linear model. Firstly, the proposed analytical model is validated with a numerical model utilizing the finite-element method. Subsequently, various combinations of soil parameters and loading conditions that affect the examined problem are investigated with realistic input data taken from the offshore section of the high-pressure natural-gas pipeline TAP (Trans Adriatic Pipeline) in the Adriatic Sea. Finally, useful conclusions are drawn regarding the applicability and the efficiency of the proposed approach.  相似文献   

Effects of changes in canopy interception on stream runoff response and recovery following clear-cutting of a Japanese coniferous forest in Fukuroyamasawa Experimental Watershed in Japan     

Tomoki Oda  Tomohiro Egusa  Nobuhito Ohte  Norifumi Hotta  Nobuaki Tanaka  Mark B. Green  Masakazu Suzuki 《水文研究》2021,35(5):e14177

Understanding changes in evapotranspiration during forest regrowth is essential to predict changes of stream runoff and recovery after forest cutting. Canopy interception (Ic) is an important component of evapotranspiration, however Ic changes and the impact on stream runoff during regrowth after cutting remains unclear due to limited observations. The objective of this study was to examine the effects of Ic changes on long-term stream runoff in a regrowth Japanese cedar and Japanese cypress forest following clear-cutting. This study was conducted in two 1-ha paired headwater catchments at Fukuroyamasawa Experimental Watershed in Japan. The catchments were 100% covered by Japanese coniferous plantation forest, one of which was 100% clear-cut in 1999 when the forest was 70 years old. In the treated catchment, annual runoff increased by 301 mm/year (14% of precipitation) the year following clear-cutting, and remained 185 mm/year (7.9% of precipitation) higher in the young regrowth forest for 12–14 years compared to the estimated runoff assuming no clear-cutting. The Ic change was −358 mm/year (17% of precipitation) after cutting and was −168 mm/year (6.7% of precipitation) in the 12–14 years old regrowth forest compared to the observed Ic during the pre-cutting period. Stream runoff increased in all seasons, and the Ic change was the main fraction of evapotranspiration change in all seasons throughout the observation period. These results suggest that the change in Ic accounted for most of the runoff response following forest cutting and the subsequent runoff recovery in this coniferous forest.  相似文献   

Modelling the effect of changing precipitation inputs on deep soil water utilization          下载免费PDF全文

Ji Qi  Daniel Markewitz  David Radcliffe 《水文研究》2018,32(5):672-686

Forests in the Southeastern United States are predicted to experience future changes in seasonal patterns of precipitation inputs as well as more variable precipitation events. These climate change‐induced alterations could increase drought and lower soil water availability. Drought could alter rooting patterns and increase the importance of deep roots that access subsurface water resources. To address plant response to drought in both deep rooting and soil water utilization as well as soil drainage, we utilize a throughfall reduction experiment in a loblolly pine plantation of the Southeastern United States to calibrate and validate a hydrological model. The model was accurately calibrated against field measured soil moisture data under ambient rainfall and validated using 30% throughfall reduction data. Using this model, we then tested these scenarios: (a) evenly reduced precipitation; (b) less precipitation in summer, more in winter; (c) same total amount of precipitation with less frequent but heavier storms; and (d) shallower rooting depth under the above 3 scenarios. When less precipitation was received, drainage decreased proportionally much faster than evapotranspiration implying plants will acquire water first to the detriment of drainage. When precipitation was reduced by more than 30%, plants relied on stored soil water to satisfy evapotranspiration suggesting 30% may be a threshold that if sustained over the long term would deplete plant available soil water. Under the third scenario, evapotranspiration and drainage decreased, whereas surface run‐off increased. Changes in root biomass measured before and 4 years after the throughfall reduction experiment were not detected among treatments. Model simulations, however, indicated gains in evapotranspiration with deeper roots under evenly reduced precipitation and seasonal precipitation redistribution scenarios but not when precipitation frequency was adjusted. Deep soil and deep rooting can provide an important buffer capacity when precipitation alone cannot satisfy the evapotranspirational demand of forests. How this buffering capacity will persist in the face of changing precipitation inputs, however, will depend less on seasonal redistribution than on the magnitude of reductions and changes in rainfall frequency.  相似文献   

海洋表层沉积物中金属镉的来源解析     

谭赛章  杨涛  可愚  刘材材  张昊飞 《海洋通报》2019,38(6):683-689

利用2015年8月份对长江口及其邻近海域表层沉积物的监测数据,基于主成分分析/绝对主成分分数(PCA/APCS)受体模型定量解析了重金属元素镉(Cd)的可能来源,并结合地统计学插值了Cd的源贡献量的空间分布状况,结果表明沉积物中镉污染主要存在3个可能来源,源头及贡献率分别为工业污染(18.8%)、陆地径流输入(66.0%)、生物活动等自然因素(13.6%),并且各个源头贡献量具有不同的空间分布状况,其中工业污染的高值区主要集中在靠近陆地区域,陆地径流输入的分布呈现由近岸向外海逐减降低的特征,生物活动等自然因素的高值区主要集中在远离陆地的外海区域。  相似文献   

弧形海岸裂流的数值模拟研究   总被引：3，自引：0，他引：3  

汪鸿  朱首贤  李训强  张文静  聂屿 《海洋学报(英文版)》2018,37(3):21-30

弧形海岸波浪产生的裂流严重危害人类活动，但是目前对其特征缺乏充分认识。本文对Haller物理模型实验和三亚大东海的数值模拟表明FUNWAVE模式具有较好的裂流模拟能力。基于该模式进行了多种弧形海岸条件的裂流数值模拟，给出裂流的一些特征：（1）海岸弯曲度增大，裂流增强；（2）海岸坡度对裂流有比较大的影响，太陡或太平缓的海岸不利于形成裂流；（3）海岸尺寸减小，裂流减弱；（4）波高和波周期增大，裂流增强，但是对于某些海岸而言，0.4m波高可能就存在危害比较大的裂流。  相似文献   

Three-dimensional finite element simulation of fracture propagation in rock specimens with pre-existing fissure(s) under compression and their strength analysis     

Ramin Pakzad  Shanyong Wang  Scott W. Sloan 《国际地质力学数值与分析法杂志》2020,44(10):1472-1494

A FORTRAN program, consistent with the commercially available finite element (FE) code ABAQUS, is developed based on a three-dimensional (3D) linear elastic brittle damage constitutive model with two damage criteria. To consider the heterogeneity of rock, the developed FORTRAN program is used to set the stiffness and strength properties of each element of the FE model following a Weibull distribution function. The reliability of the program is assessed against available experimental results for granite cylindrical specimens with a throughgoing, flat and inclined fissure. The calibration procedure of the material parameters is explained in detail, and it is shown that the compressive to tensile strength ratio can have a substantial influence on the failure response of the specimens. Numerical simulations are conducted for models with different levels of heterogeneity. The results show a smaller load bearing capacity for models with less homogeneity, representing gradual coalescence of fully damaged elements forming throughout the models during loading. The maximum load bearing capacity is studied for various combinations of inclination angles of two centrally aligned, throughgoing and flat fissures of equal length embedded in cylindrical models under uniaxial and multiaxial loading conditions. The key role of the compressive to tensile strength ratio is highlighted by repeating certain simulations with a lower compressive to tensile strength ratio. It is proven that the peak loads of the rock models with sufficiently small compressive to tensile strength ratios containing two throughgoing fissures of equal length are similar, provided that the minimum inclination angles of the models are the same. The results are presented and discussed with respect to the existing experimental findings in the literature, suggesting that the numerical model applied in this study can provide useful insight into the failure behaviour of rock-like materials.  相似文献   

渤、黄海生态环境模拟的参数敏感度空间差异分析     

罗辰奕  聂红涛  张海彦 《海洋学报》2019,41(8):85-96

随着海洋生态系统模型的发展，生态变量增多，众多生物过程参数量值的确定成为制约生态环境模拟的瓶颈问题，生态系统结构区域性要求模型中的生态参数具有区域差异。为探究不同海区的关键参数及参数敏感度的空间差异，本研究在渤、黄海建立了ROMS-CoSiNE物理–生物耦合的高分辨率生态系统模型，并对13种生态参数的敏感度空间分布进行分析。结果表明:南黄海中部与渤海及近岸海域的敏感度差异较大。渤海敏感度最大的参数为决定光合速率的浮游植物P-I曲线初始斜率，其次为浮游动物捕食半饱和常数和浮游动物最大捕食率。而南黄海中部敏感度最大的参数为浮游动物最大捕食率，其次为浮游植物死亡率和浮游植物P-I曲线初始斜率。结合敏感度分布及浮游植物生物量收支得出，渤海水体透明度较南黄海偏低、浮游植物生长光限制较强，是引起浮游植物P-I曲线初始斜率敏感度在渤海高于黄海的主要原因。浮游动物最大捕食率及浮游植物死亡率的敏感度空间差异，受渤、黄海浮游植物生物量差异的影响，与生态系统中的高度非线性特征有关。  相似文献   

Implementation of a coupled plastic damage distinct lattice spring model for dynamic crack propagation in geomaterials          下载免费PDF全文

Chao Jiang  Gao‐Feng Zhao 《国际地质力学数值与分析法杂志》2018,42(4):674-693

This paper studies dynamic crack propagation by employing the distinct lattice spring model (DLSM) and 3‐dimensional (3D) printing technique. A damage‐plasticity model was developed and implemented in a 2D DLSM. Applicability of the damage‐plasticity DLSM was verified against analytical elastic solutions and experimental results for crack propagation. As a physical analogy, dynamic fracturing tests were conducted on 3D printed specimens using the split Hopkinson pressure bar. The dynamic stress intensity factors were recorded, and crack paths were captured by a high‐speed camera. A parametric study was conducted to find the influences of the parameters on cracking behaviors, including initial and peak fracture toughness, crack speed, and crack patterns. Finally, selection of parameters for the damage‐plasticity model was determined through the comparison of numerical predictions and the experimentally observed cracking features.  相似文献   

湿地水文过程与植被响应研究进展与案例分析     

徐力刚  赖锡军  万荣荣  王晓龙  李相虎 《地理科学进展》2019,38(8):1171-1181

生态水文学是20世纪90年代兴起的一门研究生态过程和生态格局水文机制的新学科。湖泊湿地作为中国5大类天然湿地类型之一,湖泊湿地生态水文学的研究业已成为生态水文学的研究的一个重要对象和分支,其核心在于研究湖泊湿地生态系统中多时空尺度的水文与生物格局、过程的耦合特征及其相互作用。论文首先概述了湖泊湿地生态水文学的研究进展,包括其基本理论,内涵、外延及其主要研究内容;凝练了湖泊湿地生态水文学研究的方法体系、思路及框架;针对目前湖泊湿地生态水文学研究中存在的问题及薄弱环节,提出了湖泊湿地生态水文学未来研究的发展趋势和亟需加强研究的重点方向。在此基础上,以长江中游的典型通江湖泊湿地——鄱阳湖湿地为例,通过开展的湖泊湿地生态水文过程与模拟研究的典型案例,阐述了鄱阳湖湖泊湿地生态水文过程的变化及其植被响应研究的最新进展和研究成果。论文对于构建涵盖湖泊湿地水资源、湖泊湿地生态景观格局与流域管理、湖泊湿地生物多样性保育以及湿地资源可持续利用与生态管理等方向在内的战略研究体系,完善湿地生态水文研究与流域生态与管理的技术支撑体系具有重要的指导意义和实践价值。  相似文献