POTENTIAL FOR VEGETATION‐BASED RIVER MANAGEMENT IN DRYLAND,SALINE CATCHMENTS

The approaches used to manage rivers have been developed and adapted to many different problems and settings. Because of their relatively low cost, vegetation‐based approaches implemented at the reach, landholder and catchment scales have become the foundation for river management in most landscapes. In many dryland agricultural catchments, secondary (anthropogenic) salinity caused by clearing native vegetation has resulted in rising saline groundwater, streamflow salinity values that exceed seawater and severe the degradation of riparian vegetation communities. The potential effectiveness of vegetation‐based strategies in these landscapes remains largely unknown, yet these strategies are still widely pursued. This study initially investigated the patterns of vegetation recovery and recolonization following a large flood in a saline river that disturbed the system. A conceptual model was developed to describe spatial patterns of where different vegetation types had regrown and recovered in relation to controls exerted by streamflow salinity, surface texture characteristics, topography and reach morphology. Using this model, vegetation‐based river management options for different reaches were developed, and their potential effectiveness in stabilizing reaches was investigated using a 1‐D hydraulic modelling approach. This study finds that in a dryland catchment with high stream salinity (20 000–93 000 mg L^?1), there is still a strong potential for successful vegetation‐based management, but only in selected reaches. Results showed that changes in stream power and channel velocity were not associated with the areas of most severe vegetation degradation. Rather, there is a complex interplay between channel morphology, channel slope and places of potential vegetation growth within a reach. This paper outlines an approach to evaluate the potential success of vegetation‐based river management in saline landscapes. It identifies the need to prioritize investment based on the following: an understanding of factors controlling revegetation potential, the likely impact of revegetation in mitigating adverse channel changes and the proximity of reaches to high‐value infrastructure and biodiversity assets. Copyright © 2011 John Wiley & Sons, Ltd.     

影响岩质路堑边坡表层土稳定性因素的敏感度分析

针对渝怀铁路鱼嘴车站岩质路堑植被边坡,采用直剪切试验获得边坡表层绿色防护层的物理力学参数。在此基础上,选取5个影响边坡表层土稳定性的因素(坡度、土层厚度、重度、粘聚力、内摩擦角),采用数学及数理统计的方法进行敏感度分析,得出各影响因素的敏感度顺序为内摩擦角>坡度>重度>土层厚度>粘聚力,分析表明绿色防护层的内摩擦角是控制其稳定性的主控因素。     

基于温度植被干旱指数的黄河源区土壤表层含水量反演

为了对黄河源区的土壤表层含水量进行反演与时空分析,利用黄河源区2006年第65—321天MODIS温度和植被指数产品数据,计算了温度植被干旱指数(TVDI),构建了不同像元尺度窗口的LST/NDVI斜率与实测表层土壤相对含水量之间的线性关系,比较了不同尺度像元窗口的拟合效果。分析结果表明:9×9像元窗口的拟合效果(回归系数R2为0.65)优于其他像元窗口尺度;季节尺度的拟合精度(回归系数R2为0.76)优于长时间序列的拟合精度;夏季模拟值与实测值的均方根误差为0.09,模拟精度满足实验要求,可用于黄河源区短时间序列的土壤表层含水量反演。     

不同覆盖层厚度对土石坝动力响应的影响

为研究深厚基础覆盖层上土石坝的动力稳定性问题,利用有限元弹塑性动力分析方法进行覆盖层土石坝动力响应分析,通过输入一条实测地震波,研究不同覆盖层厚度对土石坝坝体动力响应的影响规律。结果表明,不同覆盖层厚度对土石坝位移和加速度动力响应规律的影响不同,土石坝动力响应并非随覆盖层厚度的增加而逐渐增大,而是存在一个临界厚度,超过这个厚度以后,动力响应有所降低。     

基于RS和GIS的LUCC研究——以重庆市万州区为例

通过利用遥感、地理信息系统相结合的技术方法,解译万州区2000年与2004年2期遥感影像,获得该地区相关数据的矢量图及定量统计数据,结合万州区自身特点,运用包含4个指数在内的指标分析了土地利用和土地覆盖变化(LUCC)特征,为该区土地的合理利用提供决策依据。结果表明:土地整体变化不大,单一动态度则各有千秋,其中较为明显的是建设用地增长突出,以及林地和耕地的减少,因此为实现该区可持续发展,必须采取措施保护耕地和林地,加强城市建设用地的管理。     

漓江流域沿岸风光带植被覆盖度的遥感动态监测与估算

以1990、2008年TM影像和2001年ETM＋影像为数据源,研究漓江精华段沿岸风光带植被覆盖度的动态变化规律,采用归一化植被指数（NDVI）像元二分模型,半定量估算了研究区的植被覆盖度,生成了不同时相的植被覆盖度等级图及面积转移矩阵,并结合植被覆盖度的监测结果对研究区植被覆盖度的变化趋势进行建模分析.结果表明,研究区1990、2001和2008年均以高植被覆盖度等级为主,估算的面积分别为207.058、216.538和232.795 km2.1990-2008年间,研究区内植被覆盖度稳定不变的区域占总面积的44.887％,减少和增加的区域分别占总面积的22.077％和33.036％,说明植被覆盖度总体上呈现增加的趋势;结合1990-2001年和2001-2008年的变化分析结果,植被覆盖度变化趋势是先略微增加,后显著增加,与植被覆盖度均值走势一致,从定量遥感的角度证明了漓江精华段沿岸风光带的绿色生态环境得到了快速的改善.     

An experimental study of the incipient bed shear stress partition in mobile bed channels filled with emergent rigid vegetation

This paper investigates the bed shear stress based on the condition of the incipient motion of sediment in a uniform-flow flume covered with emergent rigid vegetation,which is represented by arrays of circular cylinders arranged in a regular pattern.A total of 148 tests are performed to observe the influence of the vegetation density,bed slope,flow depth and sediment size on the bed shear stress.The tests reveal that when the sediment is in incipient motion,the resistances acting on the flow passing the rigid vegetation contain the vegetation resistance and the bed shear stress.This shear stress could be divided into two parts:the grain shear stress and the shear stress caused by sand dunes,which are the deformed bedform with the sediment incipient motion.An empirical relationship between the shear stress of the sand dune and vegetation density,the Froude number,the apparent vegetation layer velocity is developed.     

基于Solidworks的缸盖试漏机的设计

针对现有的传统浸水试漏机二维设计方法的不足,利用Solidworks软件,介绍了缸盖浸水试漏机的总体结构,详细阐述了试漏机的浸水机构、封堵夹具等关键零部件的三维设计,并实现了整机的虚拟装配,为产品的系列化奠定了基础．     

基于PDX的盖板级进模设计

根据盖板冲压件的结构特点,采用Pro/E的扩展模块PDX设计盖板级进模.分析盖板的冲压工艺性,设计条带布局.以条带布局为基础,创建模架、工作零件和其它组件,并将它们装配从而得到盖板级进模的整体结构.应用PDX软件实现盖板级进模组件的3D参数化设计,提高了设计效率,保证了设计质量.     

北京市土地利用变化对地表温度的影响分析

运用遥感(RS)和地理信息系统(GIS)技术,对北京1995年至2005年的土地利用时空变化特征进行了分析,并分析了土地利用变化对区域内地表温度的影响。北京在1995年至2000年的土地利用变化较小,随后五年城镇面积大量扩张,占用了大量的耕地和林地。北京地表温度等级较高的区域在数量上呈逐年增加的趋势,同时在空间分布上呈现从分散向城市中心集中的趋势。构建了TVX空间研究土地利用变化对地表温度的影响,计算了不同土地利用类型转变为建设用地的变化向量长度,并选取未变化的土地利用类型的平均温度作为控制点,消除不确定性因素,分析得出变化向量的幅度依次是:有林地>水域>其他林地>灌木林地>草地>耕地,由此可以看出,林地和水域对缓解地表热环境作用较强,在城市规划中,要尽量保护林地和水域。