共查询到20条相似文献,搜索用时 0 毫秒
1.
The hyporheic zone (HZ), which is the region beneath or alongside a streambed, plays an important role in the stream's ecology. The duration that a water molecule or a solute remains within the HZ, or residence time (RT), is one of the most common metrics used to evaluate the function of the HZ. The RT is greatly influenced by the streambed's hydraulic conductivity (K), which is intrinsically difficult to characterize due to its heterogeneity and anisotropy. Many laboratory and numerical studies of the HZ have simplified the streambed K to a constant, thus producing RT values that may differ from those gathered from the field. Some studies have considered the heterogeneity of the HZ, but very few have accounted for anisotropy or the natural K distributions typically found in real streambeds. This study developed numerical models in MODFLOW to examine the influence of heterogeneity and anisotropy, and that of the natural K distribution in a streambed, on the RT of the HZ. Heterogeneity and anisotropy were both found to shorten the mean and median RTs while increasing the range of the RTs. Moreover, heterogeneous K fields arranged in a more orderly pattern had longer RTs than those with random K distributions. These results could facilitate the design of streambed K values and distributions to achieve the desired RT during river restoration. They could also assist the translation of results from the more commonly considered homogeneous and/or isotropic conditions into heterogeneous and anisotropic field situations. 相似文献
2.
Various subsurface flow systems exhibit a combination of small‐scale to large‐scale anisotropy in hydraulic conductivity (K). The large‐scale anisotropy results from systematic trends (e.g., exponential decrease or increase) of K with depth. We present a general two‐dimensional solution for calculation of topography‐driven groundwater flow considering both small‐ and large‐scale anisotropy in K. This solution can be applied to diverse systems with arbitrary head distribution and geometry of the water table boundary, such as basin or hyporheic flow. In a special case, this solution reduces to the well‐known Tóth model of uniform isotropic basin. We introduce an integral measure of flushing intensity that quantifies flushing at different depths. Using this solution, we simulate heads and streamlines and provide analyses of flow structure in the flow domain, relevant to basin analyses or hyporheic flow. It is shown that interactions between small‐scale anisotropy and large‐scale anisotropy strongly control the flow structure. In the classic Tóth flow model, the flushing intensity curves exhibit quasi‐exponential decrease with depth. The new measure is capable of capturing subtle changes in the flow structure. Our study shows that both small‐ and large‐scale anisotropy characteristics have substantial effects that need to be integrated into analysis of topography‐driven flow. 相似文献
3.
Variations in the average and turbulent characteristics of under-ice flow are studied and their possible influence on the living conditions of flora and fauna in rivers in winter are discussed. 相似文献
4.
The Hydrogeology of an Induced Streambed Infiltration Area 总被引:1,自引:0,他引:1
Perry H. Rahn 《Ground water》1968,6(3):21-32
5.
6.
Ye Zhang 《Ground water》2014,52(3):343-351
Modeling and calibration of natural aquifers with multiple scales of heterogeneity is a challenging task due to limited subsurface access. While computer modeling plays an essential role in aquifer studies, large uncertainty exists in developing a conceptual model of an aquifer and in calibrating the model for decision making. Due to uncertainties such as a lack of understanding of subsurface processes and a lack of techniques to parameterize the subsurface environment (including hydraulic conductivity, source/sink rate, and aquifer boundary conditions), existing aquifer models often suffer nonuniqueness in calibration, leading to poor predictive capability. A robust calibration methodology is needed that can address the simultaneous estimations of aquifer parameters, source/sink, and boundary conditions. In this paper, we propose a multistage and multiscale approach that addresses subsurface heterogeneity at multiple scales, while reducing uncertainty in estimating the model parameters and model boundary conditions. The key to this approach lies in the appropriate development, verification, and synthesis of existing and new techniques of static and dynamic data integration. In particular, based on a given set of observation data, new inversion techniques can be first used to estimate aquifer large‐scale effective parameters and smoothed boundary conditions, based on which parameter and boundary condition estimation can be refined at increasing detail using standard or highly parameterized estimation techniques. 相似文献
7.
宽级配砾质土应力路径试验研究 总被引:1,自引:0,他引:1
对某土石坝工程的宽级配砾质土进行了三轴等应力比应力路径试验,试验分别模拟了土石坝施工填筑期及蓄水期可能的应力路径,研究了宽级配砾质土在复杂应力状态下的应力应变特性。研究表明,砾质土心墙料在等主应力比和等主应力增量比应力路径作用下,应力应变表现出较好的线性关系;在竣工期,其平均主应力p(或剪应力q)与体应变ε_v及剪应变ε_s的曲线关系都为幂函数形式,ε_v—ε_1、ε_3—ε_1关系均可用线性函数来表示,而在蓄水期,各应力与应变之间的曲线关系则基本上都可以用线性关系来表示。本文研究明确了复杂应力路径下宽级配砾质土的应力应变关系,为建立宽级配砾质土的应力应变本构模型提供了一个重要线索。 相似文献
8.
9.
10.
11.
Reynold Chow Hao Wu Jeremy P. Bennett Jürnjakob Dugge Thomas Wöhling Wolfgang Nowak 《Ground water》2019,57(3):378-391
This study determines the aspects of river bathymetry that have the greatest influence on the predictive biases when simulating hyporheic exchange. To investigate this, we build a highly parameterized HydroGeoSphere model of the Steinlach River Test Site in southwest Germany as a reference. This model is then modified with simpler bathymetries, evaluating the changes to hyporheic exchange fluxes and transit time distributions. Results indicate that simulating hyporheic exchange with a high-resolution detailed bathymetry using a three-dimensional fully coupled model leads to nested multiscale hyporheic exchange systems. A poorly resolved bathymetry will underestimate the small-scale hyporheic exchange, biasing the simulated hyporheic exchange towards larger scales, thus leading to overestimates of hyporheic exchange residence times. This can lead to gross biases in the estimation of a catchment's capacity to attenuate pollutants when extrapolated to account for all meanders along an entire river within a watershed. The detailed river slope alone is not enough to accurately simulate the locations and magnitudes of losing and gaining river reaches. Thus, local bedforms in terms of bathymetric highs and lows within the river are required. Bathymetry surveying campaigns can be more effective by prioritizing bathymetry measurements along the thalweg and gegenweg of a meandering channel. We define the gegenweg as the line that connects the shallowest points in successive cross-sections along a river opposite to the thalweg under average flow conditions. Incorporating local bedforms will likely capture the nested nature of hyporheic exchange, leading to more physically meaningful simulations of hyporheic exchange fluxes and transit times. 相似文献
12.
13.
Environmental and sanitary estimation of small-river water quality is made in the zone of influence of gold-mining facilities in Krasnoyarsk Region. The estimates are based on data on the hydrochemical regime and the characteristics of phytoplankton, microphyto-periphyton, macrozoobenthos, and ichthyofauna collected during the vegetation period of 2000. 相似文献
14.
15.
16.
Sokolova O. V. Vyruchalkina T. Yu. Solomonova I. V. Dobrovol’skii S. G. 《Water Resources》2021,48(1):7-17
Water Resources - A joint data repository on flowage lakes of the world and long-term flow variations in the rivers they regulate has been formed. The specific features of the flowage lake... 相似文献
17.
Guan-Wei Lin 《Water Resources》2019,46(5):780-788
Water Resources - Chemistry variations in the rivers are key indexes of weathering mechanisms. This paper presents a chemical variation examination of water samples acquired from 11 Taiwanese... 相似文献
18.
INTRODUCTIONAs Intnns。c properlyd]ohs,Q value Is closely related to the physical cond。tlons(such aspressure,fluid saturalon,and v。scoslty,etc.).And generally speaking,the。e attenuation Is。resensitive to the vanatlon of physical conditions than the velocity does(Best et al,1994),therefor。asure。nt Of Q value Is very m叩oltantlnl4。m扣y expenments.There re删Ww幼sic*t。"theQ value,such as spectral rat。。(Toks6z et al,1979),resonance bar(Wyllie et al,1962),andst。ss-st。。n on… 相似文献
19.
20.
Water Resources - Linearized equations of two-dimensional hydraulics have been analyzed by the method of small perturbations within a wide range of alluvial features sizes at large values of Froude... 相似文献