华北平原区地温梯度与基底构造形态的关系

本文根据部分实测温度资料和有限单元法的数值模拟计算结果,研究了华北平原区地温梯度和地表热流值与基底构造形态的关系,分析了盖层相对厚度、基岩侧界面倾角以及不同岩石热导率比值对地温梯度和地表热流分布图式的影响,并讨论了地壳浅部热流的折射和再分配问题。在此基础上,提出了华北平原区地温梯度和热流值基底构造形态的相关直线校正法,即根据不同构造部位上钻孔的实测地温梯度和盖层相对厚度的相关直线推算区域平均地温梯度和具代表性区域热流值的方法。     

北部湾盆地地温异常影响因素探讨

北部湾盆地地温场的不均一性除与基岩埋深有一定关系外,在很大程度上与活动热流体有关。含油气钻孔或含油气构造带大多分布在地温梯度和热流值较高的部位。压实作用及烃的生成所产生的压力促使热流体沿同生断裂以“幕式喷发”的方式发生运移,而流体所携带的巨大热量却不受盖层和构造圈闭等因素的影响向上传递,从而导致在地表(海底)形成高热流异常。     

Back‐calculation of bedload transport in steep channels with a numerical model

In August 2005 severe flood events occurred in the Alps. A sediment routing model for steep torrent channel networks called SETRAC has been applied to six well‐documented case study streams with substantial sediment transport in Austria and Switzerland. For these streams information on the sediment budget along the main channel is available. Flood hydrographs were reconstructed based on precipitation data and stream gauges in neighbouring catchments. Different scenarios are modelled and discussed regarding sediment availability and the effect of armouring and macro‐roughness on sediment transport calculations. The simulation results show the importance of considering increased flow resistance for small relative flow depth when modelling bedload transport during high‐intensity flood events in torrents and mountain rivers. Without any correction of increased flow resistance using a reduced energy slope, the predicted bedload volumes are about a factor of 10 higher on average than the observed values. Simulation results were also used for a back‐calculation of macro‐roughness effects from bedload transport data, and compared with an independent estimate of flow resistance partitioning based on flow resistance data. Copyright © 2010 John Wiley & Sons, Ltd.     

Contribution de la gravimétrie à l'étude de la structure de la plaine de Mornag (nord est de la Tunisie): implications hydrogéologiques

Résumé

Cette étude est basée sur l'analyse des données gravimétriques; elle a pour but d'améliorer la connaissance de la structure de la plaine de Mornag. La carte de l'anomalie résiduelle a d'abord été calculée à partir de la carte de l'anomalie de Bouguer en enlevant un gradient régional. La résiduelle calculée fournit des informations sur la variation de la densité dans le bassin de Mornag. Afin de mettre en évidence les différentes structures dans le bassin, nous avons calculé la magnitude du gradient horizontal (MGH). Cette technique a permis de déterminer des linéaments gravimétriques représentant l'emplacement des contrastes de densité, et de déduire une carte structurale de la zone d'étude. Cette carte constitue un document très utile pour orienter l'exploration des ressources en eau dans la plaine de Mornag.

Citation Farhat, B., Benassi, R., Jallouli, C. & Ben Mammou, A. (2010) Contribution de la gravimétrie à l'étude de la structure de la plaine de Mornag (nord est de la Tunisie): implications hydrogéologiques. Hydrol. Sci. J. 55(8), 1396–1404.     

Effect of sill spacing and sediment size grading on scouring at grade‐control structures

Sequences of arti?cial steps are sometimes used to reproduce the natural step–pool morphology of high‐gradient streams. The depth, length and shape of the scour holes in gravel‐bed rivers can be predicted reasonably using recently developed formulae. However, the properties of the scour holes can sometimes be affected by the distance between structures. This effect is called ‘geometrical interference’ and leads to a reduction of the scour hole compared to its potential size. Geometrical interference may occur in sequences of arti?cial steps in high‐gradient torrents, where structures are sometimes built at distances of a few tens of metres apart, but may also apply to natural step–pool systems. In this paper, a series of tests have been conducted to determine the effect of bed sill spacing and sediment grading on the potential erosion by jets forming over the sills. A new formula is derived, applicable to high‐gradient streams (slope > 0·04), which can be applied to the special case of scour holes developed by interfering sills. Sediment size gradation, not accounted for in previous formulae, is found to have a signi?cant effect on the scour dimensions and is included in the new predictive formula. Copyright © 2004 John Wiley & Sons, Ltd.     

Parameter identification for on‐line model updating in hybrid simulations using a gradient‐based method

To improve the efficiency of model fitting, parameter identification techniques have been actively investigated. Recently, the applications of parameter identification migrated from off‐line model fitting to on‐line model updating. The objective of this study is to develop a gradient‐based method for model updating to advance hybrid simulation also called hybrid test. A novel modification of the proposed method, which can reduce the number of design variables to improve the identification efficiency, is illustrated in detail. To investigate the model updating, simulated hybrid tests were conducted with a 5‐story steel frame equipped with buckling‐restrained braces (BRBs) utilized in the shaking table tests conducted in E‐Defense in Japan in 2009. The calibrated analytical model that was verified with the test results can serve as the reference model. In the simulated hybrid tests, the physical BRB substructure is numerically simulated by utilizing a truss element with the 2‐surface model identical to the part of the reference model. Such numerical verification allows simulation of measurement errors for investigation on the performance of the proposed method. Moreover, the feasibility of sharing the identified parameter values, which were obtained from the physical substructure responses, with the relevant numerical models is also verified with the artificial component responses derived from the physical experiments.     

A numerical study on the occurrence of flowing wells in the discharge area of basins due to the upward hydraulic gradient induced wellbore flow

The occurrence of flowing wells in basins has been found to be closely related to the discharge area with an upward hydraulic gradient. Unfortunately, previous studies on upward gradient induced wellbore flow with equaling total inflow (Q_in) in the deep and total outflow (Q_out) in the shallow could not explain the occurrence of flowing wells. By representing wells using the MNW2 Package imbedded in MODFLOW 2005, we obtain the exchange of groundwater between the aquifer and the well in the discharge area of 3D unit basins and identify three scenarios: Q_in = Q_out, Q_in > Q_out > 0 and Q_in > Q_out = 0. The relationship of Q_in > Q_out well explains why flowing wells only develop in a limited part of the discharge area. Sensitivity analysis shows that well location, water table undulation, and basin length–depth ratio do not change the profile of the ratio of cumulative flow rate in a flowing well to total inflow (Q_v/Q_in) versus the relative elevation in the inflow segment, z_in*, but could significantly change the length of the inflow segment; well depth could change both the length of the inflow segment and the profile of Q_v/Q_in versus z_in*. Based on the numerical results in homogeneous and isotropic basins with different basin length–depth ratios in the current study, the ratio of inflow in the lower half part of a flowing well to the total inflow is found to be at least 67% and could be close to 100%, indicating that water at the outlets of flowing wells with long open sections is mainly from the deep part of the well.     

A jadeite–quartz–glaucophane rock from Karangsambung, central Java, Indonesia

High-pressure metamorphic rocks are exposed in Karangsambung area of central Java, Indonesia. They form part of a Cretaceous subduction complex (Luk–Ulo Complex) with fault-bounded slices of shale, sandstone, chert, basalt, limestone, conglomerate and ultrabasic rocks. The most abundant metamorphic rock type are pelitic schists, which have yielded late Early Cretaceous K–Ar ages. Small amounts of eclogite, glaucophane rock, garnet–amphibolite and jadeite–quartz–glaucophane rock occur as tectonic blocks in sheared serpentinite. Using the jadeite–garnet–glaucophane–phengite–quartz equilibrium, peak pressure and temperature of the jadeite–quartz–glaucophane rock are P  = 22 ± 2 kbar and T  = 530 ± 40 °C. The estimated P–T conditions indicate that the rock was subducted to ca 80 km depth, and that the overall geothermal gradient was ∼ 7.0 °C/km. This rock type is interpreted to have been generated by the metamorphism of cold oceanic lithosphere subducted to upper mantle depths. The exhumation from the upper mantle to lower or middle crustal depths can be explained by buoyancy forces. The tectonic block is interpreted to be combined with the quartz–mica schists at lower or middle crustal depths.     

Paleogeothermal gradient and geologic thermal history of the Turpan-Hami Basin, Xinjiang

Synthetical research has been done on the geological thermal history of the Turpan-Hami Basin by using vitrinite reflectance, fluid inclusion geothermometry and fission track. The geotcmperature of the Turpan-Hami Basin has the character that suggests higher temperature in the past, in the east and south of the basin, and in the areas of large-fracture, and lower temperature in the present day and in the west and north of the basin. This feature is controlled by the difference of burial depth of basement and heat flow values, which made Permian source rock mature in the late Triassic and Jurassic source rock mature at the end of Jurassic and the early Tertiary. Project supported by the Chinese Tnrpan-Hami Oil Field cooperation project.     

Sodicity effects on hydrological processes of sodic soil slopes under simulated rainfall

Soil salinization can occur in many regions of the world. Soil sodicity affects rainfall‐runoff relationships and related erosion processes considerably. We investigated sodicity effects on infiltration, runoff and erosion processes on sodic soil slopes for two soils from China under simulated rainfall. Five sodicity levels were established in a silt loam and a silty clay with clay contents of 8.5% and 46.0%, respectively. The soils, packed in 50 cm × 30 cm × 15 cm flumes at two slope gradients (22° and 35°), were exposed to 60 min of simulated rainfall (deionized water) at a constant intensity of 125 mm h^?1. Results showed that, for both soils, increasing soil sodicity had some significant effects on hydrological processes, reducing the infiltration coefficient (pr = ?0.69, P  < 0.01) and the quasi‐steady final infiltration rate (pr = ?0.80, P  < 0.01), and increasing the mean sediment loss (pr = 0.39, P  < 0.05); however, it did not significantly affect the cumulative rainfall to ponding (P  > 0.05). Moreover, increasing sodicity significantly increased the Reynolds number and the stream power (pr = 0.78 and 0.66, P  < 0.01, respectively) of the runoff, decreased Manning roughness and Darcy–Weisbach coefficient (pr = ?0.52 and ?0.52, P  < 0.05, respectively), but did not significantly affect the mean flow velocity, mean flow depth, Froude number and hydraulic shear stress. Stream power was shown to be the most sensitive hydraulic variable affecting sediment loss for both soils. Furthermore, as sodicity increased, the values of critical stream power decreased for both the silt loam (R ² = 0.29, P  < 0.05) and the silty clay (R ² = 0.49, P  < 0.05). The findings of this study were applied to a real situation and identified some negative effects that can occur with increasing sodicity levels. This emphasized the importance of addressing the influences of soil sodicity in particularly high risk situations and when predicting soil and water losses.