山区流域暴雨洪水的数值模拟

基于中尺度天气研究预报模式WRF和流域水文模型对我国夏季山区的暴雨洪水进行模拟研究。首先,结合新安江水文模型和TOPMODEL自主研发了一个动态结合地面地下产流计算的新水文模型XXT,并选取成熟的天气研究预报模式(WRF)的模拟结果作为XXT的输入进行洪水模拟。其中WRF模拟采取3重区域嵌套模拟再现了2007和2008年夏季山东南部沂沭泗河流域的3次暴雨过程。模拟结果表明,WRF对暴雨的时空分布有较好的模拟与预测能力,模拟结果与观测一致性较好,逐时降水过程较观测更为连续,峰值有一定差异,总量略有偏大。WRF模拟的逐时站点表层土壤湿度与自动站观测的变化趋势一致,峰值偏大,空间分布与降水有着较好的响应关系。总格点径流深的计算结果同样与降水对应得较好,基本能重现出暴雨-径流过程的时空变化特征。其后,利用收集的实测降水资料率定XXT的模型参数,进而将WRF模拟的降水和潜在蒸散发输入到XXT进行流域出口洪水流量的模拟,其中2008年的模拟结果取得了0.91的效率系数,而2007年2次个例由于偏高的降水,使得洪峰流量较观测有偏大,但与观测的时间相关系数高达为0.89和0.91。研究对于山区暴雨洪水的预报预警和防汛决策具有一定的参考价值。     

甘肃黄渚镇“8.12”暴洪泥石流灾害类型特征及成因分析

黄渚镇位于地质灾害高频发地区—陇南山地的北部。2010年8月12日,黄渚镇一带遭遇百年不遇的暴雨,形成暴洪灾害,并诱发泥石流、滑坡、矿坑突水、道路岸坡坍塌等次生灾害,给当地群众及厂坝铅锌矿作业区造成重大灾害与损失。通过对本次暴洪泥石流灾害的特征及成因进行分析,得出：百年不遇的暴雨是灾害形成的直接原因,而人类不合理的活动则加重了灾害的危害程度,同时当地的地形地貌、地层岩性等条件也是灾害形成的有利条件。     

Flash-flood and bedload dynamics of desert gravel-bed streams

Comparatively little is known about the hydrology of desert flash-floods despite the extent of the world's drylands. There is even less known about their sedimentary behaviour and particularly about the movement of coarse material as bedload. The results of an intense field monitoring programme carried out on an ephemeral gravel-bed stream in the northern Negev Desert are presented. In this semi-arid setting, flow duration analysis indicates that the channel is hydrologically active for 2% of the time, or about seven days per year, and that overbank flow can be expected for only 0·03% of the time—about three hours per year. Multipeaked flood hydrographs are the norm, reflecting many factors including the arrival of separate slugs of discharge from contributing subcatchments. The passage of the initial flood bore is surprisingly slow, but the rising limb of the flood hydrograph is rapid with a median time of rise of 10 minutes, in keeping with expected flash-flood behaviour. Bedload flux is high, averaging 2·67 kg s⁻¹ m⁻¹ during the period that the channel carries flow. This gives very high bedload sediment yield despite the infrequent and short duration of flood flows and matches the high yield of suspended sediment. The relationship between bedload flux and boundary shear stress is simple, in contrast with perennial gravel-bed streams, and the exponent of the log–log relationship is 1·52. Of great value is that the behaviour of the Nahal Eshtemoa corroborates a pattern established by the authors previously in a smaller tributary stream. © 1998 John Wiley & Sons, Ltd.     

Evaluation of past,present and future tools for radar-based flash-flood prediction in the USA

Abstract

The societal impacts of flash floods are more significant than any other weather-related hazard. They are often manifested in the form of damage to infrastructure, flooding of roadways and bridges, creating deadly hazards to motorists and inundation of crops and pasture. Some of these hazards can be anticipated and thus mitigated given effective warning systems. This study describes the tools proposed over recent decades in the USA to predict flash flooding and evaluates them using a common observational data set. Design recommendations for flash-flood forecasting systems are provided, taking into account today's availability of high-resolution rainfall data at scales commensurate with flash flooding, their archives, spatial data sets to describe physiographic properties, and ever-increasing computational resources.

Editor D. Koutsoyiannis; Guest editor R.J. Moore

Citation Gourley, J.J., Flamig, Z.L., Hong, Y., and Howard, K.W., 2014. Evaluation of past, present and future tools for radar-based flash-flood prediction in the USA. Hydrological Sciences Journal, 59 (7), 1377–1389. http://dx.doi.org/10.1080/02626667.2014.919391     

The sedimentology of an ephemeral fluvial–aeolian succession

Ephemeral fluvial systems are commonly associated with arid to semi-arid climates. Although their complex sedimentology and depositional settings have been described in much detail, depositional models depicting detailed lateral and vertical relationships, and interactions with coeval depositional environments, are lacking compared to well-recognized meandering and braided fluvial systems. This study critically evaluates the applicability of current models for ephemeral fluvial systems to an ancient arid fluvial example of the Lower Jurassic Kayenta Formation of the Colorado Plateau, USA. The study employs detailed sedimentary logging, palaeocurrent analysis and photogrammetric panels across the regional extent of the Kayenta. A generic model that accounts for the detailed sedimentology of a sandy arid ephemeral fluvial system (drawing upon both ancient and geomorphological studies) is developed, along with analysis of the spatial and temporal interactions with the aeolian setting. Results show that the ephemeral system is dominated by laterally and vertically amalgamated, poorly channelized to sheet-like elements, with abundant upper flow regime flat beds and high sediment load structures formed between periods of lower flow regime conditions. Through interaction with a coeval aeolian system, most of the fluvial deposits are dominated by sand-grade sediment, unlike many modern ephemeral fluvial systems that contain a high proportion of conglomeratic and/or finer grained mudstone and siltstone deposits. During dominantly fluvial deposition, high width to thickness ratios are observed for channelized and sheet-like elements. However, with increasing aridity, the aeolian environment becomes dominant and fluvial deposition is restricted to interdune corridors, resulting in lower width to thickness ratio channels dominated by flash-flood and debris-flow facies. The data presented here, coupled with modern examples of ephemeral systems and flood regimes, suggest that ephemeral flow produces and preserves distinctive sedimentological traits that can not only be recognized in outcrops, but also within core.     

城市山洪灾害风险评价——以云南省文山县城为例

山洪灾害风险评价对于减灾防灾决策和管理非常重要。本文介绍基于遥感和GIS方法的应用,探讨一种快速、简便而且较为准确的城市山洪灾害风险评价方法。以发生于1998年7月26日文山城20年一遇山洪灾害为实例,将GIS的数字高程模型与实测的山洪水位和洪峰流量结合进行淹没分析,研究表明采用该方法可以模拟准确山洪泛滥范围,并计算淹没水深分布。根据不同水深指标,应用GIS工具完成了山洪灾害危险分区。本研究利用高分辨率遥感影像提供承灾体类型的可靠和准确数据用于易损性分析和期望损失评估的价值计算。根据典型区财产损失的抽样调查,建立了不同承灾体类型与水深的关系,并确定其损失率;应用GIS空间数据处理和分析的集成方法完成了复杂的损失评估。在此基础上,按期望损失程度进行分区划分而完成山洪风险评价。研究结果表明基于GIS和RS方法进行山洪风险评价效果良好,值得推广应用于其他洪水泛滥区。