深埋沉管隧道基础碎石垫层变形特性试验研究

沉管隧道基础往往采用条带垄沟状先铺碎石垫层,该碎石垫层作为桩基与沉管结构传力构造的工程经验极少,为了解碎石垫层在工程荷载下的变形特性、传力机制及垄沟尺寸,及结构水平移动、回淤、垄沟偏位、桩顶倾斜等工程因素对其的影响等方面进行了物理模型试验研究。研究表明：（1）碎石级配的选择应同时考虑压缩模量、孔隙率、粒径等多种因素,过小粒径级配不适宜用于基础垫层;（2）垄沟的存在会大幅降低碎石垫层的压缩模量,压缩主要是由压密变形和垄沟导致的碎石颗粒侧向“挤出”造成;（3）支撑桩段碎石垫层的极限承载能力约为480 kPa,碎石垫层作为桩顶传力构造,受力变形机制复杂,个别影响因子十分敏感,需采取措施控制桩顶应力水平在碎石垫层极限承载能力范围内。     

围堰防渗墙与复合土工膜联接型式试验研究

防渗墙上接土工膜是围堰常用的防渗体系,两者变形是否协调是决定防渗成败的关键。以某围堰工程为例,通过围堰防渗体系中复合土工膜的受力分析和复合土工膜与砂砾料界面的直剪摩擦试验,研究了土工膜与填料之间的相互作用,提出了保证土工膜不被拉断应满足的条件。另外,通过离心模型试验监测复合土工膜在堰体与防渗墙变形过程中的应变,揭示了复合土工膜的受力性状和联接部位的破坏机制。结果表明,在一定上覆荷载作用下复合土工膜与堰体之间的摩阻力超过其所承受的拉伸力,导致预留伸缩节不能发挥作用;复合土工膜下部风化砂的固结变形使之与刚性防渗墙之间产生较大的差异沉降以及防渗墙与上游堰体的水平脱离,两种变形不协调均可导致与防渗墙联接部位的土工膜因受拉而破坏,在该基础上提出了改进的土工膜与防渗墙的联接型式和铺设方法。试验成果为指导围堰防渗体系的分析和设计提供了可靠的依据。     

Sensitivity of interfacial hydraulics to the microtopographic roughness of water‐lain gravels

Flow within the interfacial layer of gravel‐bed rivers is poorly understood, but this zone is important because the hydraulics here transport sediment, generate flow structures and interact with benthic organisms. We hypothesized that different gravel‐bed microtopographies generate measurable differences in hydraulic characteristics within the interfacial layer. This was tested using a high density of spatially and vertically distributed, velocity time series measured in the interfacial layers above three surfaces of contrasting microtopography. These surfaces had natural water‐worked textures, captured in the field using a casting procedure. Analysis was repeated for three discharges, with Reynolds numbers between 165000 and 287000, to evaluate whether discharge affected the impact of microtopography on interfacial flows. Relative submergence varied over a small range (3.5 to 8.1) characteristic of upland gravel‐bed rivers. Between‐surface differences in the median and variance of several time‐averaged and turbulent flow parameters were tested using non‐parametric statistics. Across all discharges, microtopographic differences did not affect spatially averaged (median) values of streamwise velocity, but were associated with significant differences in its spatial variance, and did affect spatially averaged (median) turbulent kinetic energy. Sweep and ejection events dominated the interfacial region above all surfaces at all flows, but there was a microtopographic effect, with Q2 and Q4 events less dominant and structures less persistent above the surface with the widest relief distribution, especially at the highest Reynolds number flow. Results are broadly consistent with earlier work, although this analysis is unique because of the focus on interfacial hydraulics, spatially averaged ‘patch scale’ metrics and a statistical approach to data analysis. An important implication is that observable differences in microtopography do not necessarily produce differences in interfacial hydraulics. An important observation is that appropriate roughness parameterizations for gravel‐bed rivers remain elusive, partly because the relative contributions to flow resistance of different aspects of bed microtopography are poorly constrained. © 2014 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.     

Impact of channel bar form and grain size variability on estimated stranding risk of juvenile brown trout during hydropeaking

Hydropeaking leads to artificial fluctuations in discharge and corresponding water levels with pronounced dewatering areas between base and peak flow along gravel bars and channel banks. In the present study, 16 hydropeaking reaches in Austria were investigated to assess possible differences in the estimated stranding risk for young of the year brown trout according to different gravel bar types and differences in microtopography roughness. Based on hydrodynamic‐numerical modelling, a predictive habitat modelling approach was implemented in the study design. Accompanied by grain size sampling along the various channel bars, a conceptual stranding risk model (SRM) was developed. The results showed that a high variability in estimated stranding risk exists for the tested sites considering discharge ratios of 1:3, 1:5 and 1:10. With respect to the discussion of establishing legal thresholds for ramping ratios in discharge, it was documented that, exemplarily, a discharge ratio base flow/peak flow of 1:5 (winter base flow conditions) could cause minor differences in the spatial extent of dewatering areas and the related estimated stranding risk for juvenile brown trout compared to a ratio of 1:2 for summer base flow conditions. Microtopographic roughness was addressed due to sampling and analysis of grain size distributions. Statistical testing of grain size distributions revealed significant differences between the surface material compositions of the investigated gravel bars. Those differences are evident, particularly for the coarser fraction (d₉₀), which is important as cover for young of the year brown trout. These aspects of grain size in habitat use and hydraulics have been addressed in the conceptual SRM. The results showed that point bar morphology, in particular, was less sensitive to the risk of stranding compared to, for example, alternating gravel bars. Considering the multiple pressures for alpine rivers, the improvement of structural features due to bar formation and related self‐forming processes is discussed as a possible alternative for future mitigation measures to reduce the negative impacts of hydropeaking. Copyright © 2014 John Wiley & Sons, Ltd.     

Delivering environmental flows in the Murray-Darling Basin (Australia)—legal and governance aspects

Abstract

The hydrology of water-dependent ecosystems around the world has been altered as a result of flow regulation and extraction for a variety of purposes including agricultural and urban water supply. The flow regime of the Murray-Darling Basin in Australia is no exception, with attendant impacts on the health of the environment. Restoration of parts of the flow regime is a key feature of environmental flow delivery. However, environmental flow delivery in a system that is managed primarily to provide a secure and stable supply for irrigation presents challenges for managers seeking to return more natural flow variability in line with ecosystem requirements. The institutional arrangements governing releases of water from storage can influence the ability of managers to respond to natural cues, such as naturally rising flows in a river. As such, the legal and governance aspects of environmental flow delivery are likely to be important influences on the outcomes achieved.

Editor Z.W. Kundzewicz; Guest editor M. Acreman

Citation Banks, S.A. and Docker, B.B., 2014. Delivering environmental flows in the Murray-Darling Basin (Australia)—legal and governance aspects. Hydrological Sciences Journal, 59 (3–4), 688–699.     

Assessment of environmental flows under limited data availability: case study of the Acheloos River,Greece

Abstract

The lower course of the Acheloos River is an important hydrosystem in Greece, heavily modified by a cascade of four hydropower dams upstream, which is now being extended by two more dams in the upper course. The design of the dams and hydropower facilities that are in operation has not considered any environmental criteria. However, in the last 50 years, numerous methodologies have been proposed to assess the negative impacts of such projects to both the abiotic and biotic environment, and to provide decision support towards establishing appropriate constraints on their operation, typically in terms of minimum flow requirements. In this study, seeking a more environmentally-friendly operation of the hydrosystem, we investigate the outflow policy from the most downstream dam, examining alternative environmental flow approaches. Accounting for data limitations, we recommend the basic flow method, which is parsimonious and suitable for Mediterranean rivers, whose flows exhibit strong variability across seasons. We also show that the wetted perimeter–discharge method, which is an elementary hydraulic approach, provides consistent results, even without using any flow data. Finally, we examine the adaptation of the proposed flow policy (including artificial flooding) to the real-time hydropower generation schedule, and the management of the resulting conflicts.

Editor Z.W. Kundzewicz; Guest editor M. Acreman

Citation Efstratiadis, A., Tegos, A., Varveris, A., and Koutsoyiannis, D., 2014. Assessment of environmental flows under limited data availability: case study of the Acheloos River, Greece. Hydrological Sciences Journal, 59 (3–4), 731–750.     

雅安地区青衣江流域第四纪阶地特征分析

雅安青衣江流域阶地非常发育。通过砾石的岩性、粒度、扁平面的统计,研究区阶地砾石主要来源于青衣江上游地区,在万古场古青衣江流向由北东改为向东,在阳坪现代青衣江流向一致为东南,流速有逐渐减小的趋势。根据阶地测年和阶面相对高程分析,从早更新世至全新世本区至少有7次构造抬升,万古场阶地最大抬升幅度达85 m,最大抬升速率为0.532 mm/a,阳坪阶地抬升幅度最大达到52 m,最大抬升速率为1.25 mm/a。     

广西桂中1井井下油气地球化学特征及其指示意义

长期以来,桂中坳陷以其良好的地质条件为中外地质学家所瞩目,通过对桂中1井纵向上不同层段岩屑样品的油气地球化学特征研究,以典型油气层、生油层、储油层以及盖层化探异常组合、异常形态及其特征为依据,并用烃类比值、甲烷碳同位素、三维荧光等方法进行属性判断,针对桂中1井不同异常区段（不同地层）从化探角度进行评价。并且对桂中凹陷勘探潜力的判断提供地球化学依据。     

南京地区新近纪砂砾层的沉积环境演变

南京地区分布着一套新近纪的松散砂砾沉积,曾被统称为雨花台砾石层。依据岩性、层序、沉积构造等特征,我们解译了4个地点砂砾层的沉积环境。研究发现,洞玄观组的沉积环境类似于曲流河沉积,六合组类似于砂质辫状河沉积,雨花台组则属于砾质辫状河沉积。沉积环境的不同印证了前人的观点,即这些砂砾层是不同时期形成。古流向显示,从中新世到更新世早期本区的流域格局与目前的大体一致。而河流沉积环境的演化,却指示河道的坡降具有不断增大的趋势。我们认为这可能是全球海平面不断下降导致侵蚀基准面降低所引起的,而差异性的构造运动似乎不是主要的驱动因素。     

Assessment of Dynamic Characteristics for Compaction Piles with Geophysical Logging in Soft Ground

In this paper, a case study was performed on a sand compaction pile (SCP) and a gravel compaction pile (GCP) to estimate the dynamic characteristics and the improvement effect of soft ground. The dynamic elastic modulus, shear modulus, bulk modulus, and Poisson's ratio were estimated and the dynamic characteristics were analyzed using the compression and shear wave velocity of the improved ground based on the results of suspension P- and S-wave (PS) logging. The results revealed that the dynamic properties were increased in the order of unimproved subsoil and improved subsoil using SCP and GCP. The increase in the effects of dynamic properties with each replacement ratio of SCP was not large, whereas a good increase in the effects was observed in the case of the improved subsoil with GCP. Consequently, it was presented that the resistance characteristics against the seismic loading of GCP are excellent. As a result of analyzing the density distribution of the improved subsoil through density field logging, the overall density distribution gradually exhibits increasing trends in the order of unimproved subsoil and improved subsoil with SCP and GCP. Thus, the improvement effect of GCP was relatively high in comparison with the same replacement ratio of SCP.