Steady state analysis of unsaturated flow above a shallow water-table aquifer drained by ditches

The one-dimensional pressure head profile above a fixed water-table was studied for different steady infiltration rates. As shown in previous studies, when the infiltration rate (q_in) is less than the soil saturated hydraulic conductivity (Ks), this profile can be divided into two parts: (1) from the water-table surface (z₀) to an elevation z_γ, the pressure head varies from 0 to a value h_γ such as K(h_γ)=−q_in; (2) above the elevation z_γ the pressure head is constant and equal to h_γ. Above the water-table the zone where the pressure head is variable has been called ‘transition zone’. Its height is shown to be highly variable and to depend on soil properties as well as on the infiltration rate. This transition zone is not the ‘capillary fringe’ as defined by Gillham (Gillham R.W., 1984. The capillary fringe and its effect on water-table response. J. Hydrol. 67, 307–324). Numerical experiments performed with HYDRUS-2D^® for the case of a water-table drained by parallel ditches have shown that the height of the transition zone is similar in the one-dimensional profile and in the two-dimensional system as long as the local slope of the water-table is small. This result is important since in a two-dimensional system, the transition zone is the place where all the horizontal component of the unsaturated flow occurs. The ratio of the horizontal component of the unsaturated flow vs the total horizontal flow in both the unsaturated and saturated zones has been computed. For a given soil, this ratio decreases as the infiltration rate increases; for a given infiltration rate, the soil with the thinnest transition zone transfers the largest amount of water above the water-table.     

末次冰期东亚季风气候的数值模拟研究

利用一个Ｔ４２全球大气环流谱模式模拟了现代及末次冰期极盛时期边界条件下的东亚季风气候，并与中国区域内古气候变化的地质证据了对比，综合分析表明，末次末期时东亚冬季风强盛，夏季风衰退，气候大陆度增加。年平均气温普遍下降，我国华南，西北东部至华北，东北地区分别比现代降温２－４℃、８－１０℃及１０℃以上；季风多降水明显减少，与现代相比，东南沿海，江淮至华北，东北地区年降水量分别减少７０－８０％，６０－７０     

天津局地气候的反演建模及其研究

利用天津月平均温度Ｔ、气压Ｐ和雨量Ｒ的时间序列反演出一组近似描写天津（Ｔ－Ｐ－Ｒ）局地气候的动力方程，并对其演化特性及内部相互作用机制进行了研究。     

整体大地测量的理论和实际应用

本文着重介绍整体大地测量确定性参数模型的理论和整体大地测量的误差分析方法，并进一步说明整体大地测量研究的理论意义和实际应用价值。     

杜家垞—一碗水库段地震成因讨论

分析了杜家垞——碗水库段于1993年5月3日—15日发生的145次地震。认为这些地震是由清江隔河岩水库第一阶段前期蓄水老滑坡体重新活动引起的,属滑坡型水库地震.     

新疆的干旱环境与滑坡,泥石流及其防治对策

新疆的干旱气候环境,导致荒漠广布.受温差悬殊制约,风化作用强烈.不论山地或平原,松散物均较发育,由于降水时空分布不均,崩,滑,流具有明显的时空分布特征,大雨、暴雨往往集中在夏季。暴雨洪流,融雪洪流成了引发泥石流的动力。特殊的内陆环境条件,决定新疆降水量有限。受水动力条件不足制约,新疆的滑坡多系小型土滑,且往往与泥石流共生。换句话说,滑坡为泥石流提供了物源。因此,对新疆滑坡,泥石流的治理,应本着近期治标,长期治本的原则,以土木系统工程治表、生物系统工程治本。与此同时,还要强调社会系统工程,作为实施各项防护举措的保证。通过综合治理,以促进改善生态环境。     

利用遥感技术进行毛家庄滑坡调查和稳定性分析

本文介绍了利用遥感技术对毛家在滑坡所作的调查和稳定性分析。毛家在滑坡为一特大型老滑坡。从卫星图像上可看出，滑坡正好处在渭河主干断裂带内。从航空像片上可清楚地圈定出滑坡的范围，并能发现一系列表明滑坡复活的迹象。从对影响滑坡的几个因素进行的分析判断，该滑坡有再次滑动的可能。     

地下水动态观测网优化设计研究

本文采用状态空间分析法,通过对地下水流系统输入变量、输出变量及地下水动态测量值的研究,提出了地下水流系统确定一随机性数值模型。运用该模型的模拟解,进行地下水动态观测网优化设计。该方法把地下水动态观测网密度、位置及观测频率优化与地下水流系统结合起来研究。为了克服该模型计算量大的缺陷,本文提出了一种改进算法,使这一观测网优化方法适于在微机上实现,减少了计算工作量。该方法曾用于陕西某地区地下水位动态观测网的优化设计,取得了显著经济效益。     

Deterministic uncertainty in landscapes

Deterministic complexity (chaos) may be common in geomorphic systems, but traditional definitions may have limited practical utility for empirical geomorphology. These definitions are based on sensitivity to initial conditions, which in geomorphology are both unknown and unknowable. Further, chaos analysis depends on distinguishing deterministic complexity from stochastic complexity. This is problematic in geomorphology because some stochastic complexity is virtually always present in addition to any chaos that may be present. While it is important to recognize that some complex, apparently random patterns may derive from inherent non-linear system dynamics, this is of limited use in explaining process–response relationships or mechanics of landscape evolution. A more general term, which subsumes chaos, is deterministic uncertainty, i.e. uncertainty associated with an identifiable but unknown or uncertain source. An analysis of landscape entropy shows that such underlying constraints produce spatial patterns which are apparently chaotic. For the case of geologic controls, the apparent contribution of deterministic chaos to the landscape entropy is a direct non-linear function of the extent of geologic constraints. However, the underlying constraints and their contribution to observed spatial patterns can also be interpreted in non-chaotic terms. Examples are given, involving geologic constraints on stream channel networks and parent material control of surface soil textures. Because both randomness and chaos may be more apparent than real, the concept of deterministic uncertainty is more useful in process geomorphology than that of chaos.     

Ground-based SAR interferometry for monitoring mass movements

An innovative technique for the remote assessment of ground displacements, based on radar interferometry and implemented using ground-based instrumentation (GB-InSAR), has been tested in recent years on a number of selected case sites. The system, known as LISA, developed by the Joint Research Centre (JRC) of the European Commission, is a ground-based radar interferometer specifically designed for field use. It is composed of two radar antennas mounted on a linear rail which horizontally slides to form a synthetic aperture. Coherent SAR processing converts the raw data into an image containing, for each pixel, information on the wave phase, which depends on the target-sensor distance. Consecutive couples of SAR images can be cross-correlated to form interferograms representing phase variations which can be directly related to ground displacement along the sight-line of the radar system, since they are acquired from exactly the same position. Several applications of the system have been conducted on a number of mass movements located in Italy, in order to validate the technique for the monitoring of landslides. GB-InSAR has proved its potential for the measurement of the superficial ground displacements of different landslide types, in terms of failure mechanism, materials involved, kinematics, water content and deformation rates. In particular conditions, such as fast-moving phenomena and inaccessible areas, the technique can be employed directly as a monitoring tool, providing multi-temporal displacement maps of the observed area. Additionally, some applications of the GB-InSAR have provided a fundamental support to decision makers during landslide emergencies, allowing the civil protection authorities to assess the risk and to manage an effective emergency response.