Feedbacks between erosion and sediment transport in experimental bedrock channels

Natural bedrock rivers flow in self‐formed channels and form diverse erosional morphologies. The parameters that collectively define channel morphology (e.g. width, slope, bed roughness, bedrock exposure, sediment size distribution) all influence river incision rates and dynamically adjust in poorly understood ways to imposed fluid and sediment fluxes. To explore the mechanics of river incision, we conducted laboratory experiments in which the complexities of natural bedrock channels were reduced to a homogenous brittle substrate (sand and cement), a single sediment size primarily transported as bedload, a single erosion mechanism (abrasion) and sediment‐starved transport conditions. We find that patterns of erosion both create and are sensitive functions of the evolving bed topography because of feedbacks between the turbulent flow field, sediment transport and bottom roughness. Abrasion only occurs where sediment impacts the bed, and so positive feedback occurs between the sediment preferentially drawn to topographic lows by gravity and the further erosion of these lows. However, the spatial focusing of erosion results in tortuous flow paths and erosional forms (inner channels, scoops, potholes), which dissipate flow energy. This energy dissipation is a negative feedback that reduces sediment transport capacity, inhibiting further incision and ultimately leading to channel morphologies adjusted to just transport the imposed sediment load. Copyright © 2007 John Wiley & Sons, Ltd.     

多部多普勒雷达同步探测三维风场反演系统

“我国重大气候和天气灾害的形成机理与预测理论研究”项目首次启用双多普勒雷达组网同步观测，如何从同步观测的暴雨资料中反演三维场，具有重要的理论和现实意义，根据项目需要，建立了国内首套多部多普勒天气雷达同步探测三维风场反演软件系统，并反演出2001年7月13日由双多普勒雷达同步观测到的一个中β尺度暴雨系统的三维风场，结果显示，该三维风场结构合理，系统能满足外场试验的要求。     

回溯时间积分格式的有效性研究

采月正压准地转模式作为动力核,用Rossby-Haurwitz波函数作为理想场,同时使用回溯时间积分格式和普通中央差格式进行数值试验.结果表明,在短时积分的情况下,回溯格式能减小数值解误差1～2个量级,而且它对时间步长的增大不敏感.因此使用回溯格式可以减少积分计算量,延长积分时效.     

GPS-RTK技术在航道测量中的应用

介绍GPS实时定位RTK(Real-TimeKinematics)技术原理及其关键性技术 ,阐述了该技术在航道测量中应用 ,得出了一些结论     

基于均匀混合假设的天然河道水质模拟方法

扩散质进入窄浅型河道后,通常采用有限差分法求解一维对流分散方程进行水质模拟,计算相对复杂。为简化计算,提出了根据河道断面特征等水力特性,将河道划分为若干单元,忽略不灵敏因子分散项对单元间扩散质交换的影响,并引入单元均匀混合假定,提出了基于均匀混合假设的天然河道水质模拟方法,建立相应的水质数学模型。算例表明,该模型运算稳定,与有限差分法模拟精度相当,但可大大简化并节省计算工作量。     

烟台海域海难事故气象条件分析及预防对策

通过对1990－1999年烟台辖区海域海难事故资料及烟台海区相关气象资料统计分析，得出烟台沿海及附近海域难事故发生的一般规律及其与气象的关系，并提出了海难事故的预防对策。     

开展国际海道测量师培训有关问题的探讨

就我国开展国际海道测量培训问题，阐述了其必要性，迫切性与可通用性，并探讨了开展国际海道测量师培训的具体实施方法。     

阿勒泰夏季大降水过程中高潜能场的时空变化特征分析

以大降水过程中触发高潜能量释放的天气系统为背景条件，以高潜能场为起报信息，对40个大降水个例进行统计、分析和归纳，概括出阿勒泰夏季大降水过程中，高潜能场的时空变化特征，从中得出预报阿勒泰夏季大降水的新指标，进一步提高了大降水预报的准确率。     

铁路沿线灾害性天气监测、预测、预警系统

针对铁路三防（防风，防沙，防洪）的需要，结合大风监测系统建设的实际，对恶劣天气气候条件下，如何保障列车运行安全进行了探讨，并提出铁路沿线灾害性天气监测，预测，预警系统。     

The 12–13 November 1999 flash flood in southern France

The flash flood that occurred on 12–13 November 1999 in meridional France is documented. This event caused 35 fatalities and severe damage to property as rainfall totals locally exceeded 550 mm in 24 h and 620 mm in 48 h.The main issue of the present study is to discuss how realistically the spatial and temporal rainfall distribution of this flash flood event can be represented with present state-of-the-art operational and research modeling frameworks. The predictability of the present event for different forecast ranges is investigated and sensitivity studies are conducted in order to discuss the influence of model physics (convection, microphysics), atmospheric moisture analysis and Mediterranean sea surface temperature forcing on the quality of the results. It is shown that the present event could be reasonably predicted on forecast ranges of 2–3 days as it was essentially determined by strong moisture advection from the Mediterranean coupled with frontal and orographical lifting. However, precipitation scores show significant sensitivity to both analysis errors and model physics.