考虑径流补给的滑坡渗流三维有限元模拟

现有数值模拟方法在模拟边坡降雨入渗时通常不能考虑径流流量补给对滑体渗流的影响,当滑床和滑带的渗透性相对于滑体极低时,会出现低估降雨入渗量、高估滑坡稳定性的现象。以Richards方程、运动波方程和有限元法为基础,提出了一种降雨时滑坡渗流数值模拟方法。该方法忽略滑床和滑带的渗流而只考虑滑体渗流过程,从而减小计算规模,也避免了因滑体与滑床(滑带)渗透性差异过大引起的数值计算困难;依据地形和滑体降雨入渗边界饱和情况,修正降雨入渗边界类型和流量,实现了考虑径流流量补给的滑坡降雨入渗简化数值模拟。对简单土质边坡降雨入渗进行数值模拟,从水量平衡与边坡渗流场两个角度,对比了考虑和不考虑径流流量补给的区别;结果表明,考虑径流流量补给时才能保证计算结果水量平衡,正确反映降雨入渗对基质吸力大幅降低的作用。

河岸浸没预测及排水沟效果研究

针对浸没预测忽略上边界入渗补给和蒸发等问题的缺陷,利用VisualModflow地下水模拟软件,建立了非稳定流数学模型,设定合理的边界条件,重点探讨了入渗系数和蒸发系数的确定方法和步骤。利用建立的数学模型,模拟计算浸没范围,并设置排水沟边界模拟排水效果。对多层地基,得出3.5m深排水沟可以将浸没范围控制在距堤脚100m范围内的结论。

堤内地下水受河水位的影响规律及其排水研究

河水位对堤内地下水有重要的影响,且河水向二岸的侧渗常导致堤内排水困难,使农作物遭受渍害。针对汉江中下游典型的二元土壤结构,利用V isualM od flow建立地下水流数学模型,模拟分析堤内地下水位和沿程“向上补给”流量随河水位变化的规律。为了排水降压,将渗流模型简化,导出排水沟深度和间距的计算公式,并用数值法验证了该处理方法的正确性。研究成果可为河岸渍害的防控提供理论依据。

The Extent of Land Use Impact on Water Regime in the Vseminka Catchment

The paper deals with the impact of land use changes on water regime. An assessment was carried out in order to determine the extent to which the main components of the water balance on the experimental catchment Vseminka have been influenced by land use changes （region Vsetinske Hills, the Czech Republic）. For this reason, the water balance model WBCM-5 was implemented for the period of 30 years in a daily step, with particular focus on the simulation of the components of direct runoff and of subsurface water recharge. In the selected years of the period 1980-2009, major changes were made in land use and significant fluctuation of rainfall-runoff regimes were observed （e.g. dry year 1992, flood year 1997 and normal year 2009）. After WBCM-5 parameter calibration it was observed that some water balance components can change in relation to substantial land use changes, even up to dozens of percent in a balance-consideration, i.e. in daily, monthly and yearly or decadal values, specifically as far as the components of interception and also of direct runoff and of subsurface water recharge are concerned. However, a different situation appeared during the investigation of significant short-term rainfall-runoff processes. There were about seven real flood events during the same period on the same catchment which were analysed using the KINFIL-2 model （time step 0.5 hr）. Land use change, positive or negative scenarios, were also analysed during this period. As opposed to long-term water balance analyses, only a 10% difference in the hydrograph peak and volume was observed. In summary, the authors have shown that it is always important to distinguish a possible land use change impact on either long-term balance or short-term runoff. Otherwise, as often found in over simplified commentaries on flood events in the mass media, the actual impact of land use changes on water regime may be misunderstood.

The discovery of surface runoff in the megadunes of Badain Jaran Desert,China,and its significance

The Badain Jaran Desert exhibits the greatest difference in altitude of all of the world's deserts.On the slopes of megadunes in the desert,there are physical and chemical deposits produced by surface runoff.In addition,we have observed rarely-seen infiltration-excess surface runoff in the megadune depressions as well as spring streams at the base of megadunes.We used electron microscopy,energy spectrum analysis,infiltration experiments,moisture content determinations and grain-size analysis to study the mineral and chemical composition of the runoff precipitates,and grain-size of the deposits associated with the runoff,together with the hydrological balance in the megadune area,and the atmospheric precipitation mechanism responsible for groundwater recharge and for supplying water to lakes.The observations of shallow runoff and infiltration-excess surface runoff indicate the occurrence of strong and effective precipitation in summer,which would provide an important source for groundwater recharge.Several lines of evidence,such as the physical and chemical deposits resulting from shallow subsurface runoff,spring streams,infiltration-excess runoff,and gravity capillary water with a moisture content of 3-6%,demonstrate that precipitation reaches the base of the megadunes through infiltration and subsequently becomes groundwater.The chemical deposits,such as newly-formed calcite and gypsum,and gray-black physical deposits,as well as different stages in the development of fan-shaped landforms resulting from shallow subsurface runoff,indicate that groundwater recharge in the area is the result of long-term precipitation,rather than intermittent individual major rainfall events.Fine sand layers with a low infiltration capacity lead to subsurface runoff emerging at the ground surface.Five factors play an important role in maintaining a positive water balance and in replenishing groundwater via rainfall:effective rainfall as a water source,the high infiltration capacity of the sands enabling rainfall to rapidly become capillary water in the dunes,low evapotranspiration rates due to the sparse vegetation,the fact that the depth of the sand layer influenced by evaporation is shallow enough to maximize the deep infiltration of rainfall,and rapidly-moving gravity capillary water in the sandy dunes.These five factors together constitute a mechanism for groundwater recharge from rainfall,and explain the origin of the groundwater and lakes in the area.Our findings represent a significant advance in research on the hydrological cycle,including groundwater recharge conditions and recharge mechanisms,in this desert region.