Comparing the hydrology of grassed and cultivated catchments in the semi‐arid Canadian prairies

At the St Denis National Wildlife Area in the prairie region of southern Saskatchewan, Canada, water levels in wetlands have been monitored since 1968. In 1980 and 1983 a total of about one‐third of the 4 km² area was converted from cultivation to an undisturbed cover of brome grass. A few years after this conversion all the wetlands within the area of grass dried out; they have remained dry since, whereas wetlands in adjacent cultivated lands have held water as before. Field measurements show that introduction of undisturbed grass reduces water input to the wetlands mainly through a combination of efficient snow trapping and enhanced infiltration into frozen soil. In winter, the tall brome grass traps most of the snowfall, whereas in the cultivated fields more wind transport of snow occurs, especially for short stubble and fallow fields. Single‐ring infiltration tests were conducted during snowmelt, while the soil was still frozen, and again in summer. The infiltrability of the frozen soil in the grassland is high enough to absorb most or all of the snowmelt, whereas in the cultivated fields the infiltration into the frozen soil is limited and significant runoff occurs. In summer, the infiltrability increases for the cultivated fields, but the grassland retains a much higher infiltrability than the cultivated land. The development of enhanced infiltrability takes several years after the conversion from cultivation to grass, and is likely due to the gradual development of macropores, such as root holes, desiccation cracks, and animal burrows. Copyright ©2002 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.     

济南市东湖水库地质灾害预测

济南市东湖水库库区不具备发生崩塌、滑坡、地面塌陷、地面沉降、泥石流、地裂缝、砂土液化的地质环境条件。水库建成使用后，可能出现坝后浸没、次生盐渍化及坝体不均匀沉降等地质灾害，应采取工程措施。     

Validity and extension of the SCS‐CN method for computing infiltration and rainfall‐excess rates

A criterion is developed for determining the validity of the Soil Conservation Service curve number (SCS‐CN) method. According to this criterion, the existing SCS‐CN method is found to be applicable when the potential maximum retention, S, is less than or equal to twice the total rainfall amount. The criterion is tested using published data of two watersheds. Separating the steady infiltration from capillary infiltration, the method is extended for predicting infiltration and rainfall‐excess rates. The extended SCS‐CN method is tested using 55 sets of laboratory infiltration data on soils varying from Plainfield sand to Yolo light clay, and the computed and observed infiltration and rainfall‐excess rates are found to be in good agreement. Copyright © 2004 John Wiley & Sons, Ltd.     

A simplified model for estimating field‐scale surface runoff hydrographs

The problem of obtaining field‐scale surface response to rainfall events is complicated by the spatial variability of infiltration characteristics of the soil and rainfall. In this paper, we develop and test a simplified model for generating surface runoff over fields with spatial variation in both rainfall rate and saturated hydraulic conductivities. The model is able to represent the effects of local variation in infiltration, as well as the run‐on effect that controls infiltration of excess water from saturated upstream areas. The effective rainfall excess is routed to the slope outlet using a simplified solution of the kinematic wave approximation. Model results are compared to averaged hydrographs from numerically‐intensive Monte–Carlo simulations for observed and design rainfall events and soil patterns that are typical of Central Italy. The simplified model is found to yield satisfactory results at a relatively small computational expense. A proposal to include a simple channel routing scheme is also presented as a prelude to extend this conceptualization to watershed scales. Copyright © 2006 John Wiley & Sons, Ltd.     

Hydrograph and unit hydrograph derivation in arid regions

Arid and semi‐arid regions expose special hydrological features that are distinctive from humid areas. Unfortunately, humid‐region hydrological empirical formulations are used directly in the arid and semi‐arid regions without care about the basic assumptions. During any storm rainfall in arid regions, rainfall, infiltration and runoff components of the hydrological cycle have impacts on water resources. The basis of the methodology presented in this paper is the ratio of runoff increment to rainfall increment during an infinitesimally small time duration. This is the definition of runoff coefficient for the same infinitesimal time duration. The ratio is obtained through rational, physical and mathematical combination of hydrological thinking and then integrated with the classical infiltration equation for the hydrograph determination. The parameters of the methodology are explained and their empirical estimations are presented. The methodology works for rainfall and runoff from ungauged watersheds where infiltration measurement can be performed. The comparison of the new approach with different classical approaches, such as the rational formula and Soil Conservation Service method, are presented in detail. Its application is performed for two wadis within the Kingdom of Saudi Arabia. Copyright © 2006 John Wiley & Sons, Ltd.     

Effect of Rainfall Intensity on Infiltration into Partly Saturated Slopes

This paper describes the development of a model to analyse the rate of infiltration and run-off experienced by a partly saturated soil slope during rainfall. The paper first reviews some of the most popular infiltration models used in geotechnical analysis, and highlights some of the problems associated with their application. One particular model, the Horton Equation is extended to include rainfall intensity directly in its formulation. The new model is shown to predict infiltration responses, which agree with field measurements. In the final section the influence of the rainfall intensity and pattern of rainfall (variation of rainfall intensity) on the infiltration response of a soil is investigated using the new model.     

暴雨型滑坡降水入渗机理分析

暴雨能诱发大量的滑坡发生,在不同地区存在不同的临界降雨值,每当雨强大于该值时,滑坡就会大面积发生,这已经被多起滑坡事件证实。一般地,入渗理论认为,当雨强大于一定值时,入渗率是常量,过强的降水会转化为地表径流,这与雨强越大滑坡越易发生、群发性越强的观察结果不一致。在斜坡体上存在大量的裂隙,它们对降水入渗有着很大的贡献,应用有限单元法分别模拟了有裂隙和无裂隙时斜坡体内瞬态渗流场的变化,并用Bishop法对不同埋深滑动面的稳定性做了计算分析。模拟结果表明：考虑裂隙时的计算结果与宏观观察结果更一致,在评价降雨入渗对斜坡稳定性的影响时,一定要充分考虑裂隙的存在,只有雨强大于一个临界值时才会有充足的降水通过裂隙渗入到斜坡深部,裂隙的影响才显著地表现出来。     

Origin of migmatites by deformation-enhanced melt infiltration of orthogneiss: a new model based on quantitative microstructural analysis

A detailed field study reveals a gradual transition from high‐grade solid‐state banded orthogneiss via stromatic migmatite and schlieren migmatite to irregular, foliation‐parallel bodies of nebulitic migmatite within the eastern part of the Gföhl Unit (Moldanubian domain, Bohemian Massif). The orthogneiss to nebulitic migmatite sequence is characterized by progressive destruction of well‐equilibrated banded microstructure by crystallization of new interstitial phases (Kfs, Pl and Qtz) along feldspar boundaries and by resorption of relict feldspar and biotite. The grain size of all felsic phases decreases continuously, whereas the population density of new phases increases. The new phases preferentially nucleate along high‐energy like–like boundaries causing the development of a regular distribution of individual phases. This evolutionary trend is accompanied by a decrease in grain shape preferred orientation of all felsic phases. To explain these data, a new petrogenetic model is proposed for the origin of felsic migmatites by melt infiltration from an external source into banded orthogneiss during deformation. In this model, infiltrating melt passes pervasively along grain boundaries through the whole‐rock volume and changes completely its macro‐ and microscopic appearance. It is suggested that the individual migmatite types represent different degrees of equilibration between the host rock and migrating melt during exhumation. The melt topology mimicked by feldspar in banded orthogneiss forms elongate pockets oriented at a high angle to the compositional banding, indicating that the melt distribution was controlled by the deformation of the solid framework. The microstructure exhibits features compatible with a combination of dislocation creep and grain boundary sliding deformation mechanisms. The migmatite microstructures developed by granular flow accompanied by melt‐enhanced diffusion and/or melt flow. However, an AMS study and quartz microfabrics suggest that the amount of melt present did not exceed a critical threshold during the deformation to allow free movements of grains.     

冲刷漏斗纵剖面形态数值模拟技术研究

提出σ坐标系垂向分层的优化方法,较好地解决了传统σ坐标变换用于底孔泄流数值模拟时存在网格边界变化的问题;采用一维水流模型为立面二维模型提供自由水面边界,即"动刚盖法"确定自由表面;根据坝前趋孔水流的流动特性和水下纵坡稳定性受力分析,分别导出σ坐标系下床面泥沙边界条件和底孔泄流初期河床滑塌的判别式。在此基础上建立底孔泄流条件下立面二维水流泥沙数学模型,并将之应用于有刚性护坦条件下冲刷漏斗形成的数值模拟。模拟结果表明,漏斗冲刷平段长度、漏斗纵坡等数值试验结果与水槽试验基本一致,验证了模型的合理性和可靠性。