A spatial assessment of hydrologic alteration caused by dam construction in the middle and lower Yellow River,China

The ‘range of variability approach’ (RVA) and mapping technique are used to investigate the spatial variability of hydrologic alterations (HA) due to dam construction along the middle and lower Yellow River, China, over the past five decades. The impacts of climate variability on hydrological process have been removed during wet and dry periods and the focus is on the impacts of human activities, such as dam construction, on hydrological processes. Results indicate the following: (1) The impacts of the Sanmenxia reservoir on the hydrologic alteration are relatively slight with a mean HA value of 0·48, ranking in the last place among the four large reservoirs. (2) Xiaolangdi reservoir has significantly changed the natural flow regime downstream with mean HA value of 0·56, ranking it in first place among the large reservoirs. (3) The results of ranked median degrees of 33 hydrologic alteration indicators for 10 stations in the Yellow River show that the hydrologic alteration of Huayuankou ranks the highest among 10 stream gauges. (4) Impacts of reservoirs on hydrological processes downstream of the dams are closely associated with the regulating activities of the reservoirs. At the same time, alterations of streamflow regimes resulting from climatic changes (e.g. precipitation variability) make the situation more complicated and more hydrological observations will be necessary for further analysis. The results of the current study will be greatly beneficial to the regional water resources management and restoration of eco‐environmental systems in the middle and lower Yellow River characterized by intensified dam construction under a changing environment. Copyright © 2008 John Wiley & Sons, Ltd.     

利用Wenzel加权谱组合法拓展GOCE重力场模型

根据GOCE和EGM08重力场模型的频谱互补性,利用Wenzel加权谱组合法构建了GOCE和EGM08的组合重力场模型。累积大地水准面误差表明,组合重力场模型具有明显的优势。美国实测GPS/水准检验结果表明,Dir4+EGM08的组合模型精度最高,比EGM08模型精度提高了8%。     

东海莫霍面起伏与地壳减薄特征初步分析

收集、整理大量由地震剖面提供的沉积层厚度资料,得到东海沉积层等厚图。对完全布格重力异常进行沉积层重力效应改正后,得到剩余重力异常,利用地震资料揭示的莫霍面深度值来约束界面反演得到东海莫霍面埋深。结果表明,东海陆架盆地莫霍面深度在25～28 km之间平缓变化,地壳厚度为14～26 km,西厚东薄;冲绳海槽盆地莫霍面深度为16～26 km,地壳厚度为12～22 km,北厚南薄。东海陆架盆地东部与冲绳海槽盆地南部地壳减薄明显,拉张因子分别达到2.6和3。初步分析认为冲绳海槽地壳以过渡壳为主,并未形成洋壳。     

基于孔压静力触探确定土体的渗透系数

近年来许多研究者致力于通过孔压静力触探(CPTU)确定土体的渗透系数,但是存在偏差大,而且不能从机制上清楚地解释孔压静力触探确定土体渗透系数的原因。为了应用孔压静力触探现场快速地确定土体的渗透系数,在总结前人对孔压静力触探确定土体渗透系数方法的研究基础上,提出孔压静力触探时锥头处呈球冠形孔隙水流动的计算模型,假定锥头处初始超孔隙水压力为负指数型分布,推导出土体渗透系数的表达式,并且结合现场实测数据,将所提出的方法与已有的方法进行对比分析。研究发现：所提出的方法扩大了现有方法的应用范围;渗透系数计算结果受锥头角度的影响较大,随着锥头角度的增大而增大;针对国际上通用的60°角的标准锥头,所提出的方法计算的渗透系数大于前人的方法,而且更接近室内外试验结果。     

A thinned lithosphere beneath coastal area of southeastern China as evidenced by seismic receiver functions

During Mesozoic to Cenozoic time, the large-scale tectono-magmatism had strongly modified the lithosphere beneath the southeastern continent of China, leaving the present-day lithosphere as a new one evolving from the ancient lithosphere that was largely removed and replaced. But this model proposed from geochemical and petrological research is urgently in need of support from seismic observational evidence. In this paper, based on the dataset recorded by the dense stations of two NE oriented broadband seismic profiles deployed in the coastal area of southeastern China(SE China), both P-wave(P-RF) and S-wave(S-RF) receiver functions were isolated. We identified Pls phase converted from the Lithosphere-Asthenosphere Boundary(LAB) in P-RFs of individual stations. Migrated Pls phase indicated a depth of 60–70 km for LAB. Inversions/comparisons of P-RF(Pls phase) and S-RF(Slp phase) waveforms together with Ps and Sp imaging for the crust and upper mantle structure further confirmed this result. P-RF and S-RF migrated images exhibit that a flat LAB is positioned at the depth of 60–70 km spreading along the profile, whereas a distinct structural change of lithospheric base appears at the Min River estuary. Both Ps and PpPs migrated images of P-RFs present an abrupt Moho drop across the Min River fault from south to north, which is consistent with previous result obtained from deep seismic sounding. By taking into consideration other geological and geophysical features such as locally high anomalies of crustal Poisson's ratios and heat flow at the Min River estuary, we infer that the Min River fault penetrates down to the Moho and may, furthermore, interfere in the deeper lithospheric structure.     

Thinning and destruction of the cratonic lithosphere:A global perspective

It has been proposed that the North China Craton(NCC)was thinned up to a thickness of100 km during the Phanerozoic,and underwent an associated craton destruction.Evidently,it is an important topic worthy of future study to understanding the mechanism of cratonic destruction and its role played in the continental evolution.After synthesized the global cratons of India,Brazil,South Africa,Siberia,East Europe(Baltic)and North America,we found that lithospheric thinning is common in the cratonic evolution,but it is not always associated with craton destruction.Most cratons was thinned by thermal erosion of mantle plume or mantle upwelling,which,however,may not cause craton destruction.Based on the studies of the North American and North China Cratons,we suggest that oceanic subduction plays an important role in caton destruction.Fluids or melts released by dehydration of the subducted slabs metasomatize the mantle wedge above and trigger extensive partial melting.More importantly,the metasomatized mantle lost its original rigidity and make craton easier to be deformed and then to be destoyed.Therefore,we suggest that the widespread crust-derived granite and large-scale ductile deformation within the continental crust can be regarded as the petrological and structural indicators of craton destruction,respectively.     

Delayed delivery from the sediment factory: modeling the impact of catchment response time to tectonics on sediment flux and fluvio‐deltaic stratigraphy

The sediment flux from a catchment is driven by tectonics and climate but is moderated by the geomorphic response of the landscape system to changes in these two boundary conditions. Consequently, catchment response time and the non‐linear behavior of landscapes in response to boundary condition change control the downstream propagation of climatic or tectonic perturbations from catchments to neighboring basins. In order to investigate the impact of catchment response time on sediment flux, we integrated a spatially‐lumped numerical model PaCMod, with new routines simulating the evolution of landscape morphology and erosion rates under tectonic and climatic forcing. We subsequently applied the model to reconstruct the sediment flux from a tectonically perturbed catchment in central Italy. Finally, we coupled our model to DeltaSim, a process‐response model simulating fluvio‐deltaic stratigraphy, and investigated the impact of catchment response time on stratigraphy, using both synthetic scenarios and a real world system (Fucino Basin, central Italy). Our results demonstrate that the differential response of geomorphic elements to tectonic and climatic changes induces a complex sediment flux signal, and produces characteristic stratigraphic architectures and shoreline trajectories. Copyright © 2014 John Wiley & Sons, Ltd.     

Implementing environmental flows in integrated water resources management and the ecosystem approach

Abstract

In many of the world’s river basins, the water resources are over-allocated and/or highly modified, access to good quality water is limited or competitive and aquatic ecosystems are degraded. The decline in aquatic ecosystems can impact on human well-being by reducing the ecosystem services provided by healthy rivers, wetlands and floodplains. Basin water resources management requires the determination of water allocation among competing stakeholders including the environment, social needs and economic development. Traditionally, this determination occurred on a volumetric basis to meet basin productivity goals. However, it is difficult to address environmental goals in such a framework, because environmental condition is rarely considered in productivity goals, and short-term variations in river flow may be the most important driver of aquatic ecosystem health. Manipulation of flows to achieve desired outcomes for public supply, food and energy has been implemented for many years. More recently, manipulating flows to achieve ecological outcomes has been proposed. However, the complexity of determining the required flow regimes and the interdependencies between stakeholder outcomes has restricted the implementation of environmental flows as a core component of Integrated Water Resources Management (IWRM). We demonstrate through case studies of the Rhône and Thames river basins in Europe, the Colorado River basin in North America and the Murray-Darling basin in Australia the limitations of traditional environmental flow strategies in integrated water resources management. An alternative ecosystem approach can provide a framework for implementation of environmental flows in basin water resources management, as demonstrated by management of the Pangani River basin in Africa. An ecosystem approach in IWRM leads to management for agreed triple-bottom-line outcomes, rather than productivity or ecological outcomes alone. We recommend that environmental flow management should take on the principles of an ecosystem approach and form an integral part of IWRM.

Editor D. Koutsoyiannis

Citation Overton, I.C., Smith, D.M., Dalton J., Barchiesi S., Acreman M.C., Stromberg, J.C., and Kirby, J.M., 2014. Implementing environmental flows in integrated water resources management and the ecosystem approach. Hydrological Sciences Journal, 59 (3–4), 860–877.     

Coupling of topographic and stratigraphic effects on seismic response of slopes through 2D linear and equivalent linear analyses

In this paper the seismic response of simple slope geometries under vertically propagating in-plane shear waves (SV waves) is assessed through two-dimensional finite element analyses to investigate the amplification of the ground motion induced by soil topography. Topographic horizontal and vertical amplification factors were evaluated through different sets of analyses focused on slopes in homogeneous half space and on slopes overlying either a rigid or a compliant bedrock. Soil was assumed to behave as a linear visco-elastic or as an equivalent-linear visco-elastic material. In the analyses the effects of slope inclination and of the characteristics of the input motion were also investigated.In order to calibrate the numerical model, the results obtained in linear visco-elastic analyses were compared with the results of parametric numerical analyses available in the literature, showing a good agreement. The results confirmed that a complex interaction exists between stratigraphic and topographic effects on the amplification of the ground motion and that the two effects cannot be evaluated independently and easily uncoupled. In the case of compliant bedrock the effect of the impedance ratio was also investigated.The results of the equivalent-linear analyses pointed out the remarkable dependence on soil non-linear behavior and, when compared to the results of linear visco-elastic analyses, showed that without accounting for soil non-linear behavior, topographic amplification factors may result underestimated.