Dissolution/precipitation kinetics of boehmite and gibbsite: Application of a pH-relaxation technique to study near-equilibrium rates

The dissolution and precipitation rates of boehmite, AlOOH, at 100.3 °C and limited precipitation kinetics of gibbsite, Al(OH)₃, at 50.0 °C were measured in neutral to basic solutions at 0.1 molal ionic strength (NaCl + NaOH + NaAl(OH)₄) near-equilibrium using a pH-jump technique with a hydrogen-electrode concentration cell. This approach allowed relatively rapid reactions to be studied from under- and over-saturation by continuous in situ pH monitoring after addition of basic or acidic titrant, respectively, to a pre-equilibrated, well-stirred suspension of the solid powder. The magnitude of each perturbation was kept small to maintain near-equilibrium conditions. For the case of boehmite, multiple pH-jumps at different starting pHs from over- and under-saturated solutions gave the same observed, first order rate constant consistent with the simple or elementary reaction: .

This relaxation technique allowed us to apply a steady-state approximation to the change in aluminum concentration within the overall principle of detailed balancing and gave a resulting mean rate constant, (2.2 ± 0.3) × 10⁻⁵ kg m⁻² s⁻¹, corresponding to a 1σ uncertainty of 15%, in good agreement with those obtained from the traditional approach of considering the rate of reaction as a function of saturation index. Using the more traditional treatment, all dissolution and precipitation data for boehmite at 100.3 °C were found to follow closely the simple rate expression:

R_net,boehmite=10^-5.485{m_OH^-}{1-exp(ΔG_r/RT)}, with R_net in units of mol m⁻² s⁻¹. This is consistent with Transition State Theory for a reversible elementary reaction that is first order in OH⁻ concentration involving a single critical activated complex. The relationship applies over the experimental ΔG_r range of 0.4–5.5 kJ mol⁻¹ for precipitation and −0.1 to −1.9 kJ mol⁻¹ for dissolution, and the pH_m ≡ −log(mH⁺) range of 6–9.6. The gibbsite precipitation data at 50 °C could also be treated adequately with the same model:R_net,gibbsite=10^-5.86{m_OH^-}{1-exp(ΔG_r/RT)}, over a more limited experimental range of ΔG_r (0.7–3.7 kJ mol⁻¹) and pH_m (8.2–9.7).     

基于HEC-RAS及GIS的川西叠溪古滑坡堰塞湖溃决洪水重建

青藏高原东南缘岷江上游地区地质环境条件十分复杂,滑坡堵江灾害及堰塞湖溃决事件频发,重建其灾害演化过程对于地区性防灾减灾和风险控制具有重要指导意义。以川西岷江上游叠溪古滑坡堰塞湖为研究对象,首先利用高精度DEM和ArcGIS软件重建了叠溪古堰塞湖的原始规模,其原始最大湖水面积为1.1×10⁷ m²,相应的湖容量为2.9×10⁹ m³;然后采用经验公式法和HEC-RAS一维水力学模型重建叠溪古堰塞湖溃决洪水的水力学特征。计算结果表明,HEC-RAS模拟的最大溃决洪水洪峰流量为73 060 m³/s,与经验公式法计算结果(74 500~76 800 m³/s,平均值76 000 m³/s)非常接近,误差小于5%。对应的最大洪水深度和流速分别为70.1 m和16.78 m/s,模拟河段的洪水淹没范围约为6.08 km²。综合误差分析推测的溃决洪峰流量误差范围为69 000~81 000 m³/s。叠溪古滑坡堰塞湖溃决洪水在世界范围内是十分罕见的,其最直接的影响是在下游数公里范围的河谷内形成大量带状或台阶状的溃坝堆积体和巨砾石堆积“阶地”,且这种影响仍延续至今,这与前人关于高能洪水水文特征和沉积特征的研究认识高度一致,证明本研究成果是非常可靠的。此外,本研究还表明,HEC-RAS一维水力模型可用于高山峡谷地区古滑坡堰塞湖溃决洪水重建研究,可为青藏高原东南缘岷江上游古环境重建和地貌演化提供参考。     

Density inhomogeneities, isostasy and flexural rigidity of the lithosphere in the Transcaspian region

The 3-D lithospheric-density model for the southeastern part of the Caspian Sea and the Transcaspian area, practically coinciding with the territory of the Turkmen Republic, has been constructed based on geophysical data and in accordance with the principle of isostasy. From the model selected the anomalous density of the subcrustal layer between the Moho discontinuity and the 100-km depth level is found to be — 100 kg/m³ under the Tien-Shan, − 50 kg/m³ under the Kopet-Dag mountain area, + 80 kg/m³ under the central region of the South Caspian basin, −50 kg/m³ under the eastern part of the basin, known as the West Turkmenian depression, and + 45 kg/m³ under the Murgab depression.

Significant disturbances of the local isostasy are determined both in the northern and central areas of the South Caspian basin and also in the area of the Kara-Bogaz swell of the Turan platform and for the Kopet-Dag foredeep. indicating a high level of stresses in the lithosphere. The shape of the Turan plate determined by the seismic profiling is accounted for by elastic deformation resulting from the forces acting on the southern edge of the plate in the area of the Turan plate-Kopet-Dag collision. The elastic thickness of the Turan plate is estimated as 25 ± 5 km. The results obtained seem to confirm the idea that the decomposition of the Turan plate has taken place in the zone of the plates interaction and the decomposed material is situated under the Kopet-Dag ridge.

We propose that the Kara-Bogaz swell is supported by the mantle material upwelling whereas the subsidence of the adjacent part of the South Caspian basin may be due to the downgoing mantle flow i.e., a small convection cell is suggested in that area.     

The usability of bottom ash as an engineering material when amended with different matrices

This study aims at investigating the utilization of bottom ash obtained from four different power stations as a construction fill and landfill bottom liner. For the matrix material, commercial powdered bentonite, construction lime and natural clay were used. Compaction tests (Standard Proctor and vibratory hammer) were carried out on the different ratios of bottom ash and matrix material. The optimum water content ranged from 40 to 45% yielding a dry density mostly ca 1 Mg m⁻³. Uniaxial compressive strength of mixtures ranges from 0.1 to 0.5 kgf cm⁻² which showed a 3–20-fold increase when tested on 28-day cured specimens. Triaxial compression tests yield varying rates of shear strength which also showed as high as an 11-fold increase for cured specimens. The hydraulic conductivity of those mixtures was mostly ca 10⁻⁴ cm s⁻¹, which is not considered to be low enough for landfill lining. Leaching tests using deionized water were also performed to investigate the possible effect of leachate produced from the mixtures on the environment. In conclusion a light density and environmentally friendly mixture is determined and proposed as construction filler.     

复杂防洪系统联合优化调度模型

建立以水库群系统安全度最大、行蓄洪区系统损失最小为目标函数,将河道堤防安全行洪考虑为约束条件的复杂防洪系统多目标递阶优化调度模型(MoHOOM),以行蓄洪区总分洪流量为协调变量,将河道水流连续方程解耦,基于大系统分解协调法建立协调层和基于粒子群算法求解底层子系统优化问题,形成三级递阶分解协调结构和相应求解方法。以淮河中游防洪系统为背景进行了实例研究,给出了水库群泄流和行蓄洪区分洪最优方案,在相同初始计算条件下,优化模型结果比实际调度降低了鲇鱼山和梅山水库0.37和0.01的安全度指标,减小下游蒋家集和润河集河段超过安全泄量以上100 m3/s和720 m3/s的洪峰流量,启用南润段行洪区致损1 256.1万元;比规则调度降低了鲇鱼山和梅山水库0.24和0.21的安全度指标,减小下游蒋家集河段超过安全泄量以上750 m3/s的洪峰流量,避免南润段行洪区损失341.6万元。模型有利于挖掘上游水库群的防洪能力,在保障河道堤防安全行洪条件下,减少下游不必要的行蓄洪区分洪损失,以系统全局寻优方式进行复杂防洪系统联合调度。     

Extreme P-, Bi-, Nb-, Sc-, U- and F-rich zircon from fractionated perphosphorous granites: The peraluminous Podlesí granite system, Czech Republic

The strongly peraluminous and P-rich, protolithionite and zinnwaldite leucogranites from Podlesí, western Krušné Hory Mts., Czech Republic, contain accessory zircon with extraordinary enrichment of several elements, which constitute trace elements in common zircon. Elements showing a not yet reported anomalous enrichment include P (up to 20.2 wt.% P₂O₅; equivalent to 0.60 apfu, formula calculated on the basis of 4 oxygen atoms), Bi (up to 9.0 wt.% Bi₂O₃; 0.086 apfu), Nb (up to 6.7 wt.% Nb₂O₅, 0.12 apfu), Sc (up to 3.45 wt.% Sc₂O₃; 0.10 apfu), U (up to 14.8 wt.% UO₂; 0.12 apfu) and F (up to 3.81 wt.% F; 0.42 apfu). Strong enrichment of P preferentially involved the berlinite-type substitution (2 Si⁴⁺  P⁵⁺ + Al³⁺) implying that significant Al may enter the Si position in zircon. Incorporation of other exotic elements is primarily governed by the xenotime (Si⁴⁺ + Zr⁴⁺  P⁵⁺ + Y³⁺), pretulite (Sc³⁺ + P⁵⁺  Zr⁴⁺ + Si⁴⁺), brabantite-type (Ca²⁺ + (U, Th)⁴⁺ + 2P⁵⁺  2Zr⁴⁺ + 2Si⁴⁺), and ximengite-type (Bi³⁺ + P⁵⁺  Zr⁴⁺ + Si⁴⁺) substitution reactions. One part of the anomalous zircons formed late-magmatically, from a strongly peraluminous, P–F–U-rich hydrous residual melt that gave rise to the zinnwaldite granite. Interaction with aggressive residual fluids and metamictization have further aided in element enrichment or depletion, particularly in altered parts of zircon contained in the protolithionite granite. Most of the zircon from F-rich greisens have a composition close to endmember ZrSiO₄ and are chemically distinct from zircon in its granite parent. This discrepancy implies that at Podlesí, granitic zircon became unstable and completely dissolved during greisenization. Part of the mobilized elements was reprecipitated in newly grown, hydrothermal zircon.     

Upper Mississippi embayment shallow seismic velocities measured in situ

Vertical seismic compressional- and shear-wave (P-and S-wave) profiles were collected from three shallow boreholes in sediment of the upper Mississippi embayment. The site of the 60-m hole at Shelby Forest, Tennessee, is on bluffs forming the eastern edge of the Mississippi alluvial plain. The bluffs are composed of Pleistocene loess, Pliocene-Pleistocene alluvial clay and sand deposits, and Tertiary deltaic-marine sediment. The 36-m hole at Marked Tree, Arkansas, and the 27-m hole at Risco, Missouri, are in Holocene Mississippi river floodplain sand, silt, and gravel deposits. At each site, impulsive P- and S-waves were generated by man-made sources at the surface while a three-component geophone was locked downhole at 0.91-m intervals.

Consistent with their very similar geology, the two floodplain locations have nearly identical S-wave velocity (V_S) profiles. The lowest V_S values are about 130 m s⁻¹, and the highest values are about 300 m s⁻¹ at these sites. The shear-wave velocity profile at Shelby Forest is very similar within the Pleistocene loess (12 m thick); in deeper, older material, V_S exceeds 400 m s⁻¹.

At Marked Tree, and at Risco, the compressional-wave velocity (V_P) values above the water table are as low as about 230 m s⁻¹, and rise to about 1.9 km s⁻¹ below the water table. At Shelby Forest, V_P values in the unsaturated loess are as low as 302 m s⁻¹. V_P values below the water table are about 1.8 km s⁻¹. For the two floodplain sites, the V_P/V_S ratio increases rapidly across the water table depth. For the Shelby Forest site, the largest increase in the V_P/V_S ratio occurs at 20-m depth, the boundary between the Pliocene-Pleistocene clay and sand deposits and the Eocene shallow-marine clay and silt deposits.

Until recently, seismic velocity data for the embayment basin came from eartquake studies, crustal-scale seismic refraction and reflection profiles, sonic logs, and from analysis of dispersed earthquake surface waves. Since 1991, seismic data for shallow sediment obtained from reflection, refraction, crosshole and downhole techniques have been obtained for sites at the northern end of the embayment basin. The present borehole data, however, are measured from sites representative of large areas in the Mississippi embayment. Therefore, they fill a gap in information needed for modeling the response of the embayment to destructive seismic shaking.     

Strain rate effect on the compressive strength of frozen sand

Cylindrical specimens of fine Ottawa sand (A.S.T.M. designation C-109), compacted at the optimum moisture content and saturated before unidirectional freezing, have been tested in uniaxial compression at a cold room temperature of —5.5°C and strain rates between 10⁻⁷ and 10⁻² s⁻¹. The results agree with an extrapolation of data obtained by Sayles and Epanchin [1], but are much higher than those obtained by both Goughnour and Andersland [2] and Perkins and Ruedrich [3] at strain rates below 10⁻⁵ s⁻¹. There is evidence that this may be due to variation in total moisture (ice) content, the conditions under which the specimens were frozen (closed system or an open system) and to the end effects at the platen—specimen interface.     

汉江上游晏家棚段全新世古洪水研究

通过对汉江上游详尽的野外考察,在湖北郧县晏家棚河段全新世黄土—古土壤地层中发现3层典型古洪水滞流沉积物。在沉积学的基础上,使用OSL技术断代,确定3期特大洪水事件分别在1 000~900 a BP,1 800~1 600 a BP和3 200~2 800 a BP期间发生。采用"古洪水SWD尖灭点高程法"确定这3期古洪水事件的洪峰水位介于176.20~176.73 m。运用Arc GIS耦合HEC-RAS水力模型,推求这3期古洪水事件的洪峰流量介于53 770~55 950 m3/s,并从多种角度验证了该模型计算结果的科学性和合理性。将此结果与实测洪水和历史洪水资料接续,构成万年尺度洪水水文数据序列,得到汉江上游晏家棚河段万年一遇和千年一遇洪水的流量分别为59 100和45 200m3/s。采用HEC-RAS模型对研究河段进行古洪水模拟,方法科学,结果可靠。将该河段洪水水文数据序列有效地延长到万年尺度,极大地提高了设计洪水的可靠性。     

南水北调对长江口粗颗粒悬沙来量的影响

探索了长江南水北调占总径流量10%情况下对长江粗颗粒悬沙(≥0.05mm)入海数量变化的可能影响。研究表明:南水北调对入海细颗粒泥沙的影响主要为南沙北调,但数量较小,在1%左右,而对粗颗粒悬沙的影响主要表现在入海流量减少导致的水体挟沙能力的降低。通过建立大通站典型枯水年(1978),平水年(1987)及洪水年(1983)月平均流量与月平均床沙质输沙率相关曲线,估算出各典型年在典型流量23000m3/s,30000m3/s与40000m3/s水平下调水流量3000m3/s时导致的入海床沙质输沙率的变化。结果表明,输沙率的相对变化在-39%至-24%之间,且在较高的流量水平下,输沙率相对变化较小,但绝对变化增大,经大通入海的床沙质数量每年约减少2350～4700万t.     

Late Quaternary basin evolution of the Gulf of Corinth: Sequence stratigraphy, sedimentation, fault–slip and subsidence rates

The Gulf of Corinth is a graben, which has undergone extension during the Late Quaternary. The subsidence rate is rapid in the currently marine part whereas uplift now affects a large part of the initially subsiding area in the North Peloponnese. In this paper, we document the rates of subsidence/uplift and extension based on new subsurface data, including seismic data and long piston coring in the deepest part of the Gulf. Continuous seismic profiling data (air gun) have shown that four (at least) major oblique prograding sequences can be traced below the northern margin of the central Gulf of Corinth. These sequences have been developed successively during low sea level stands, suggesting continuous and gradual subsidence of the northern margin by 300 m during the Late Quaternary (last 250 ka). Subsidence rates of 0.7–1.0 m kyr^− 1 were calculated from the relative depth of successive topset to foreset transitions. The differential total vertical displacement between the northern and the southern margins of the Corinth graben is estimated at about 2.0–2.3 m kyr^− 1.

Sequence stratigraphic interpretation of seismic profiles from the basin suggests that the upper sediments (0.6 s twtt thick) in the depocenter were accumulated during the last 250 ka at a mean rate of 2.2–2.4 m kyr^− 1. Long piston coring in the central Gulf of Corinth basin enabled the recovery of lacustrine sediments, buried beneath 12–13.5 m of Holocene marine sediments. The lacustrine sequence consists of varve-like muddy layers interbedded with silty and fine sand turbidites. AMS dating determined the age of the marine–lacustrine interface (reflector Z) at about 13 ka BP. Maximum sedimentation rates of 2.4–2.9 m kyr^− 1 were calculated for the Holocene marine and the last glacial, lacustrine sequences, thus verifying the respective rates obtained by the sequence stratigraphic interpretation. Recent accumulation rates obtained by the ²¹⁰Pb-radiometric method on short sediment box cores coincide with the above sedimentation rates. Vertical fault slip rates were measured by using fault offsets of correlated reflector Z. The maximum subsidence rate of the depocenter (3.6 m kyr^− 1) exceeds the maximum sedimentation rate by 1.8 m kyr^− 1, which, consequently, corresponds to the rate of deepening of the basin's floor. The above rates indicate that the 2.2 km maximum sediment thickness as well as the 870 m maximum depth of the basin may have formed during the last 1 Ma, assuming uniform mean sedimentation rate throughout the evolution of the basin.     

Studying the migration behaviour of selenate in Boom Clay by electromigration

For the disposal of high-level waste (HLW) in a deep geological formation as Boom Clay, safety assessment studies have shown that long lived ⁷⁹Se is one of the more critical fission products. Therefore, the knowledge of its migration properties (diffusion, retention) through the geological barrier (Boom Clay) is of paramount importance. The migration behaviour of selenium strongly depends on its speciation. Under reducing conditions, selenide would be the dominant species and selenium migration would mainly be controlled by the low solubility of Se(−II)-bearing minerals. However Se species are often found in redox disequilibrium and more oxidized species might also coexist. Therefore, the study of selenate migration requires attention, as it might be the most mobile selenium species in the host rock. Electromigration experiments performed with a ⁷⁵Se-labeled selenate in Boom Clay indicate a high mobility for this species. The apparent diffusion coefficient (D_app) of selenate in Boom Clay is estimated from electromigration experiments performed under different electric fields. Using two independent approaches, the value of D_app for selenate is shown to fall in the range from 1.7×10⁻¹¹ to 6.2×10⁻¹¹ m² s⁻¹. Moreover, no reduction of selenate in Boom Clay was observed.     

Oxidative dissolution of pyritic sludge from the Aznalcóllar mine (SW Spain)

As a result of the collapse of a mine tailing dam, a large extension of the Guadiamar valley was covered with a layer of pyritic sludge. Despite the removal of most of the sludge, a small amount remained in the soil, constituting a potential risk of water contamination. The kinetics of the sludge oxidation was studied by means of laboratory flow-through experiments at different pH and oxygen pressures. The sludge is composed mainly of pyrite (76%), together with quartz, gypsum, clays, and sulphides of zinc, copper, and lead. Trace elements, such as arsenic and cadmium, also constitute a potential source of pollution. The sludge is fine grained (median of 12 μm) and exhibits a large surface (BET area of 1.4±0.2 m² g⁻¹).

The dissolution rate law of sludge obtained is r=10^{−6.1(±0.3)} [O₂(aq)]^0.41(±0.04) a_H+^0.09(±0.06) g_sludge m⁻² s⁻¹ (22 °C, pH=2.5–4.7). The dissolution rate law of pyrite obtained is r=10^{−7.8(±0.3)} [O₂(aq)]^0.50(±0.04) a_H+^0.10(±0.08) mol m⁻² s⁻¹ (22 °C, pH=2.5–4.7). Under the same experimental conditions, sphalerite dissolved faster than pyrite but chalcopyrite dissolves at a rate similar to that of pyrite. No clear dependence on pH or oxygen pressure was observed. Only galena dissolution seemed to be promoted by proton activity. Arsenic and antimony were released consistently with sulphate, except at low pH conditions under which they were released faster, suggesting that additional sources other than pyrite such as arsenopyrite could be present in the sludge. Cobalt dissolved congruently with pyrite, but Tl and Cd seemed to be related to galena and sphalerite, respectively.

A mechanism for pyrite dissolution where the rate-limiting step is the surface oxidation of sulphide to sulphate after the adsorption of O₂ onto pyrite surface is proposed.     

新疆开都-孔雀河流域绿洲需水量与稳定性分析

水是绿洲存在和发展的核心, 干旱区绿洲稳定性与水密切相关. 根据2000-2009年资料, 采用蒸发系数法和定额法估算开都-孔雀河流域绿洲自然生态系统和社会经济系统综合需水量, 并对水资源约束条件下的绿洲稳定性进行初步探讨. 结果表明: 2000-2009年, 绿洲年均总需水量理论值约为54.80×10⁸ m³, 其中开都河绿洲总需水量约为20.55×10⁸ m³, 孔雀河绿洲总需水量约为21.90×10⁸ m³, 博斯腾湖区耗水量约为12.35×10⁸ m³, 与绿洲10 a平均供水量相比, 供需表现出极大地不平衡性. 水资源可承载绿洲面积(不含博斯腾湖)约为3139.66 km², 其中可承载灌溉地面积约为1395.41 km², 与绿洲10 a平均面积5 248 km²相比, 差别较大, 绿洲处于不稳定状态, 现状绿洲面积应适当收缩. 最后, 对博斯腾湖最低生态水位进行讨论, 初步把大湖最低水位定为海拔1 045 m, 小湖最低生态水位定为海拔1 046.5 m.     

Strength of frozen silt as a function of ice content and dry unit weight

A total of 45 unconfined compression tests were conducted on frozen specimens of remolded, saturated Fairbanks silt at dry unit weights ranging from 993 to 1490 kg/m³ with total water contents ranging from 0.28 to 0.58. The rate of strain was 0.005 s⁻¹ . Using the criterion that the ice matrix in the soil fractures at the first point of significant yield shown in the stress-strain curve, which occurs at less than 0.01 strain in this study, the “ice matrix strength” is shown to be nearly proportional to the volumetric ice content of the soil for these tests. The strength at 0.2 strain appears to be nearly independent of the dry unit weight and water content of the soil.     

Gum rosin (colophony): A suitable material for thermomechanical modelling of the lithosphere

We investigate the use of a ductile material with temperature-sensitive viscosity for thermomechanical modelling of the lithosphere. First, we consider the scaling of mechanical and thermal properties. For a normal field of gravity, the balance of stresses and body forces sets the stress scale, in proportion to the linear dimensions and the densities. The equation of thermal conduction sets the time scale. The activation enthalpy for creep sets the temperature scale; but the thermal expansivity provides an additional constraint on this temperature scale.

Gum rosin appears to be a suitable material for lithospheric modelling. We have measured its flow properties, at various temperatures, in a specially designed rotary viscometer with unusually low machine friction. The rosin is almost Newtonian. Strain rate depends upon stress to the power n, where 1.0 <n < 1.14. The viscosity varies over 5 orders of magnitude, from about 10² Pa s at 80°C, to about 10⁷ Pa s at 40°C. The activation enthalphy is thus about 250 kJ/mol. Measured with a needle probe, the thermal conductivity is 0.113 ± 0.001 W m⁻¹K⁻¹; the thermal diffusivity, (6±3) ×10⁻⁷ m² s⁻¹. Calculated from X-ray profiles, the thermal expansivity is about 3 × 10⁻⁴ K⁻¹. These thermal and mechanical properties make gum rosin suitable for thermomechanical models, where linear dimensions scale down by a factor of 10⁶; time, by 10¹¹; viscosity, by 10¹⁷; and temperature change, by 10¹.     

Objective regionalization of Rayleigh wave dispersion data by clustering algorithms: an application to the Mediterranean basin

The main target of the present study is an objective and automated regionalization of Rayleigh wave dispersion data for the Mediterranean basin, without a priori seismotectonic constraints, and to determine the corresponding regional shear-velocity structures. The database used is formed by almost 200 Rayleigh wavetrains corresponding to 42 regional events, with surface-wave magnitude greater than 4.5, recorded at the MedNet very-broad-band stations in the Mediterranean area. Path-averaged group velocities for the Rayleigh wave fundamental mode are derived for each available epicentre-station trajectory crossing the Mediterranean basin. After this, a principal component analysis and a clustering process are applied to local group velocities, obtained for 13 different periods from 10 to 70 s, in order to classify the Mediterranean basin into several homogeneous regions. The stochastic inversion of the averaged group velocity dispersion curve obtained for each region provides the respective shear-velocity structures, down to a depth of 150–160 km. The characteristics of these areas and their possible correlation with the main seismotectonic features of the Mediterranean region are discussed. The regional models reveal significant lateral changes in the elastic structure, with the main differences concerning particularly the upper 35–40 km. Within this depth range, low shear velocities, varying from 2.8 to 3.9 km s⁻¹, characterize the Eastern Mediterranean, whereas higher velocities, ranging from 3.0 to 4.2 km s⁻¹, are deduced for the Western Mediterranean. These results suggest a thicker crust in the eastern part, but with a greater thickness of sedimentary layers. However, for depths of between 80 and 110 km, lower shear velocities are obtained in the Western part, while higher shear velocities are derived for the Eastern Mediterranean Sea, in the Aegean Sea, Greece, the south of Italy, Sicily and Tunisia. This velocity pattern suggests an averaged thicker lithosphere under the latter areas, as the top of the asthenosphere is detected at a mean depth of 75 km for the remaining regions. This thicker lithosphere can be related to processes associated with the convergence of the Eurasian and African plates and subduction under the Calabrian and Hellenic Arcs.     

2012年洪水对黄河内蒙古段冲淤影响

2012年洪水是内蒙古河段1989年以来历时最长、洪峰流量最大的洪水过程。为了解粗泥沙对黄河内蒙古段河床冲淤变化的影响,依据宽河谷河段巴彦高勒、三湖河口和头道拐水文站实测资料,分析了内蒙古河道2012年洪水水沙特征,通过计算推移质输沙量和比较断面河底变化,探讨了粗泥沙对河底调整的影响。结果表明:2012年洪水造成粗泥沙在上游段冲刷、下游段淤积;固定低水位下过流断面存在涨冲落淤的规律;洪水过后,巴彦高勒和三湖河口低水位面积分别扩大了19 m2和29 m2,头道拐减小约100 m2。由于粗泥沙排沙不平衡,底部河床的真正高程并没有降低,防洪风险依然存在。     

珠江三角洲近年地形不均匀变化对洪季水动力特征的影响

为探明在新水沙条件和人类活动的影响下珠江三角洲河网地形变化与洪季水动力特征变化之间的关系,以1999-2008年为研究时段,基于1999年地形建立一维河网数学模型,复演珠江三角洲地区"08·6"洪水,并与"08·6"实测资料进行对比,分析河网地形变化对洪季水动力特征的影响。结果表明:①珠江三角洲河网地形整体下切加强了河道行洪能力,在遭遇洪峰30年一遇的"08·6"洪水时洪水位整体下降,三角洲顶部马口站洪水位最大降幅达到0.9 m;②河网内潮差和潮汐传播速度增大,潮区界上移至马口、三水以上;③西江河网地形下切幅度大于北江河网,地形不均匀下切导致河网节点分流比改变,西江河网洪水期分流增加2%,马口站和天河站洪峰流量增幅分别接近1 500 m^3/s和1 000 m^3/s;④西江马口站分流比随上游洪水流量增大而减小的趋势没有改变,但地形不均匀下切导致其变化梯度增大。珠江三角洲近年地形的不均匀下切,是近年珠江三角洲河网地区,特别是河网腹地洪水灾害有所减轻的主要原因之一。     

金沙江下游梯级水库运行期设计洪水及汛控水位

研究探讨梯级水库运行期设计洪水计算理论和方法,实现防洪和发电效益最大化。采用t-Copula函数建立各分区洪水的联合分布,通过蒙特卡罗法和遗传算法(GA)推求金沙江下游梯级水库的最可能地区组成;分析计算各水库运行期的设计洪水及汛控水位。结果表明:①最可能地区组成结果合理可靠,可为梯级水库运行期设计洪水的分析计算提供依据;②金沙江下游梯级水库受上游水库调蓄影响显著,向家坝水库1000年一遇设计洪峰15400m^3/s(35%),3d、7d和30d洪量的削减量(削减率)分别为35.6亿m^3(33%)、70.2亿m^3(30%)和85.0亿m^3(11%);③在不降低防洪标准的前提下,下游各水库在运行期汛控水位相比汛限水位可适当抬高,白鹤滩、溪洛渡和向家坝水库的汛控水位(汛限水位)分别为788.82m(785m)、570.67m(560m)和371.36m(370m),汛期年均发电量分别增加2.1%、6.1%和1.4%,年增发电量17.1亿kW·h。