Performance assessment of two-dimensional hydraulic models for generation of flood inundation maps in mountain river basins

Hydraulic models for the generation of flood inundation maps are not commonly applied in mountain river basins because of the difficulty in modeling the hydraulic behavior and the complex topography. This paper presents a comparative analysis of the performance of four twodimensional hydraulic models (HEC-RAS 2D, Iber 2D, Flood Modeller 2D, and PCSWMM 2D) with respect to the generation of flood inundation maps. The study area covers a 5-km reach of the Santa B-arbara River located in the Ecuadorian Andes, at 2330 masl, in Gualaceo. The model's performance was evaluated based on the water surface elevation and flood extent, in terms of the mean absolute difference and measure of fit. The analysis revealed that, for a given case, Iber 2D has the best performance in simulating the water level and inundation for flood events with 20- and 50-year return periods, respectively, followed by Flood Modeller 2D, HEC-RAS 2D, and PCSWMM 2D in terms of their performance. Grid resolution, the way in which hydraulic structures are mimicked, the model code, and the default value of the parameters are considered the main sources of prediction uncertainty.

Mountain Effect and Differences in Storm Floods between Northern and Southern Sources of the Songhua River Basin

In this study, the differences in annual rainstorm changes in the Second Songhua River Basin and the Nenjiang River basin and their causes were compared from the perspective of mountain effects. The following results were drawn: (1) Altitude effect is the primary factor leading to increased rainstorms in the southern source; (2) Slope effect primarily leads to differences of the weather systems in the two sources, and thus cause the difference of the rainstorms; (3) Slope effect is responsible for the greater fluctuation in the observed floods in the southern source. These landform differences eventually lead to the differences in the characteristics of floods in the southern and northern sources. Commensurability method was used to identify the period of rainstorms in the southern and northern sources. The results showed that although rainstorms do not appear at the same time in the two sources they are characteristic of a 10 years' period in both areas. These results can serve as hydrological references for flood control and long-term flood disaster predictions.

Extreme Flood Events over the Past 300 Years Inferred from Lake Sedimentary Grain Sizes in the Altay Mountains,Northwestern China

Understanding the temporal variations of extreme floods that occur in response to climate change is essential to anticipate the trends in flood magnitude and frequency in the context of global warming. However, long-term records of paleofloods in arid regions are scarce, thus preventing a thorough understanding of such events. In this study, a reconstruction of paleofloods over the past 300 years was conducted through an analysis of grain sizes from the sediments of Kanas Lake in the Altay Mountains of northwestern China. Results showed that grain parameters and frequency distributions can be used to infer possible abrupt environmental events within the lake sedimentary sequence, and two extreme flood events corresponding to ca. 1736–1765 AD and ca. 1890 AD were further identified based on canonical discriminant analysis(CDA) and coarse percentile versus median grain size(C-M) pattern analysis, both of which occurred during warmer and wetter climate conditions by referring to tree-ring records. These two flood events are also evidenced by lake sedimentary records in the Altay and Tianshan mountains. Furthermore, through a comparison with other records, the flood event from ca. 1736–1765 AD in the study region seems to have occurred in both the arid central Asia and the Alps in Europe, and thus may have been associated with changes in the North Atlantic Oscillation(NAO) index.

GIS-based flash flooding susceptibility analysis and water management in arid mountain ranges:Safaga Region,Red Sea Mountains,Egypt

The Safaga Region(SR)is part of the Red Sea mountain range in Egypt.Catastrophic flash flooding is now an inescapable event,wreaking havoc and causing massive loss of life and property.The majority of the floodwater,however,has been wasted as runoff to the Red Sea,which,if used wisely,could meet a fraction of the water demands for a variety of applications in this area.The current work aims to use GIS techniques to integrate remote sensing data for evaluating,mitigating,and managing flash floods in SR.The data set comprised Tropical Rainfall Measuring Mission(TRMM)thematic rainfall data,1:50,000 scale topographical map sheets,geological maps,the ASTER Digital Elevation Model(ASTER GDEM),Landsat 7 Enhanced Thematic Mapper"(ETM7+),and Landsat 8 Operational Land Imager.The flash flood risk model of SR is developed using ArcGIS-10.3 geoprocessing tools integrating all the causal factors thematic maps.The final flood risk model for the SR suggests that 57%of the total basins in the SR are at high risk of flooding.Almost 38%of all basins are at moderate flood risk.The remaining 5%of basins are less prone to flooding.Flood-prone zones were identified,suitable dam-building sites were located,and extremely probable areas for water recharge were recognized.On the basis of reliable scientific data,structural and non-structural mitigation strategies that might reduce the damage susceptibility,alleviate the sensitivity of the flash flood,and best utilize its water supply were recommended.

Long-term reconstruction of flash floods in the Qilian Mountains,China,based on dendrogeomorphic methods

In China,flash floods are one of the main natural disasters causing loss of life and damage to infrastructure.The threat of flash floods is exacerbated with climate change and increased human activities,such that the number of disasters has shown a clear upward trend in recent years.However,due to the scarcity of instrumental data or overly short timeseries,we are still lacking critical data to understand spatio-temporal patterns and driving factors of extreme flash floods.This missing knowledge is however crucial for a proper management of these hazards,especially in remote mountain environments.In forested catchments,dendrogeomorphology allows the reconstruction of past process activity based on growth disturbances(GDs)in trees that have been affected by past flash floods.Therefore,in our study,for the first time,we reconstruct past flash floods in the Qilian Mountains,northeast Tibetan Plateau,over past centuries.To this end,we sampled 99 Qinghai spruce(Picea crassifolia)trees affected by flash floods,with a total of 194increment cores,and identified 302 GDs induced by past flash floods.These GDs have been caused by at least 21 flash floods that we are able to reconstruct over the last 170 years.The position of GDs within tree rings and the intra-seasonal dating of past events also allowed discussion of the likely synoptic situations that may have led to the triggering of flash floods in the past.Logistic regression analysis confirms that significant correlation exists between cumulative maximum 5-day August-September precipitation and reconstructed flash floods,which is corresponding to the majority of scars and related tangential rows of traumatic resin ducts(TRDs)found in the latewood portion of growth rings.These results support the idea that abundant precipitation occurring at the end of the summer season and early fall is the key factor driving flash floods in our study area.Our research not only fills the gaps regarding historical flash flood histories in the Qilian Mountains,but also provides a scientific basis for the region's response to climate change and flood prevention and reduction.

A Potential Flood Hazard Caused by Tianchi Volcano Eruption in Changbai Mountain, Northeast China

Geohazards appear to be increasing in frequency globally. It is of necessity to actively manage these natural hazards to minimize loss of life and property. From an early warning perspective, this paper stresses the potential fatal flood hazard represented by the huge volume of water in Tianchi Lake, the unique geography of Changbai Mountain, and the limited flood control ability in the upstream of the Songhua River. Northeast Asian countries should keep a watchful eye on the Changbai volcano cooperatively, and Chinese government especially needs to prepare plans for fighting a flood in advance.

Effects of Erosion Control Measures on Mountain Floods： A Case Study of the Censhui River South Branch Watershed

To investigate the effects of various erosion control measures on mountain floods, a case study was conducted in Censhui River South Branch Watershed using scenario analysis and soil conservation service （SCS） methods. A distributed hydrological model was developed, and watershed parameters were determined based on satellite imagery, digital terrain models, digital maps and field investigations. Two types of erosion control measures were investigated： the variation of vegetation covers and the change of cultivation techniques. Seven scenarios were considered for the test watershed. The results show： （1） while the de-vegetation results in the increase of peak discharge, the improve of vegetation covers decreases peak discharge at watershed scale; （2） by both improving vegetation cover and enhancing terrace-cultivation technology, the peak discharge is reduced and the peak flow arrival time is delayed; （3） attention should be attached to both early warning system and measures changing the underlying surface and conveyance systems.

基于FloodArea的山洪灾害风险区划研究——以淠河流域为例

致灾临界面雨量、洪水淹没范围及深度的确定是暴雨山洪灾害风险区划的核心环节。本文以淠河流域为研究区,利用统计方法与水文模型相结合的方法确定雨-洪关系,得到致灾临界面雨量;基于FloodArea开展洪水淹没模拟,叠加承灾体信息,得到T年一遇洪水淹没风险评估与区划图。通过对2015年13号台风"苏迪罗"强降水过程的淹没反演,验证表明:无论是洪水淹没范围还是淹没水深,FloodArea模拟值与实况值均较为吻合。综合来看,淠河流域暴雨山洪灾害风险区划与评估结果较为合理;基于FloodArea模型在淠河流域具有较好的洪水淹没模拟效果,可用于暴雨洪涝灾害风险评估与预警。

基于MIKE FLOOD模型的湟水河上游洪水风险评估

湟水河上游段属于典型的山区性河段,河道比降大,暴雨洪水的突发性强,洪水流量大,历史短,具有巨大的破坏力,严重考验着河流的防洪能力。通过MIKE FLOOD耦合模型建立一二维水动力学模型评估现有防洪工程的防洪能力,预测了湟水河上游遭遇10年、50年、100年一遇洪水时的洪水风险情况,并且根据预测结果提出了相应的工程改进建议,为该地区的防洪救灾提供了技术支撑;同时根据计算结果也表明MIKE FLOOD耦合模型在山区性河流的风险评估中具有良好的适用性。

基于FloodArea的新疆依格孜牙河流域山洪灾害风险区划

以新疆依格孜牙河流域为研究区,利用流域内6个自动站2013—2017年和周边7个国家基本气象站1961—2017年降水资料,基于水动力模型FloodArea构建淹没水深和降雨量之间的函数关系,确定不同重现期的致灾临界雨量阈值。利用FloodArea模型动态模拟暴雨洪灾的淹没情况,并结合研究区承灾因子(人口分布、GDP、土地利用类型),完成该流域的暴雨洪灾风险区划。结果表明,位于该流域中下游的塔格勒克艾日克村、克孜勒陶乡、依格孜牙乡林场等属于暴雨山洪的高风险区,而海拔相对较高且处于流域上游的塔木喀拉牧场、布格拉等地属于山洪淹没的低风险区。

The Maintenance of the Blocking over the Ural Mountains during the Second Meiyu Period in the Summer of 1998

The 1998 summer-time floods at the Yangtze River basin of China, the severest in last 50 years or so, directly resulted from the abnormal extension of Meiyu (rainy season), which was related to a weak East Asian summer monsoon and persistent anomalies of extratropical circulation. The long persistence of blocking over the Ural Mountains is a conspicuous feature. The physical processes responsible for the prolonged maintenance of this key system are investigated in terms of internal forcing (transient eddy upon basic flow) and external forcing (tropical heating forcing) via diagnosis and numerical experiments in the paper. Using the adjoint method, the location and structure of optimal perturbations favorable for the development and maintenance of Ural blocking are identified, which shows an apparent coincidence with the observed storm track at the eastern Atlantic to Europe sector. The diagnosis of E-vector and the response of baroclinic stationary wave to transient forcing both suggest further that the enhanced transient eddy activity favors the occurrence and maintenance of positive anomalies. The upper-level jet and heat sources (sinks) during that period are calculated, and the results indicate that the anomaly of upper jet and tropical heating is evident. The ensemble forecasting experiments by a GCM, IAP T42L9 show that the anomalous heating over the tropics, especially over the central-western Pacific and Atlantic, favors the formation of positive anomalies of height at the Ural region. Finally, a self-sustain mechanism of positive anomalies through two-way interaction between planetary stationary wave and transient eddy under the stimulation of anomalous tropical heating is proposed.

Application and comparison of coaxial correlation diagram and hydrological model for reconstructing flood series under human disturbance

Intense human activities have greatly changed the flood generation conditions in most areas of the world, and have destroyed the consistency in the annual flood peak and volume series. For design flood estimation, coaxial correlation diagram and conceptual hydrological model are two frequently used tools to adjust and reconstruct the flood series under human disturbance. This study took a typical mountain catchment of the Haihe River Basin as an example to investigate the effects of human activities on flood regime and to compare and assess the two adjustment methods. The main purpose is to construct a conceptual hydrological model which can incorporate the effects of human activities. The results show that the coaxial correlation diagram is simple and widely-used, but can only adjust the time series of total flood volumes. Therefore, it is only applicable under certain conditions(e.g. There is a strong link between the flood peaks and volumes and the link is not significantly affected by human activities). The conceptual model is a powerful tool to adjust the time series of both flood peak flows and flood volumes over different durations provided that it is closely related to the catchment hydrological characteristics, specifically accounting for the effects of human activities, and incorporating expert knowledge when estimating or calibrating parameters. It is suggested that the two methods should be used together to cross check each other.

Influence of Flow Regime on the Vegetation Zonation along Mountain Streams in the Western Cape, South Africa

Zonation patterns of riparian vegetation have been sampled and described in mountain streams in two catchments in the Hottentots-Holland Mountains, Western Cape, South Africa. Six main vegetation types that differ in structure and species composition, are dominant along these river banks: Aquatic vegetation, Wetbanks, Palmiet, Scrub, Forest and Shrubland(Fynbos). The study aims to correlate the vegetation patterns to flooding patterns, in particular the inundation frequency and stream power. A problem arises: because these catchments are ungauged, like most mountain catchments, with the only weirs at the downstream end of the catchment. Discharge data at the weirs are extrapolated to the sites upstream by multiplication with a factor based on the size of the subcatchment that drains through a sample site. In this way, recurrence intervals for floods in mountain streams are derived. Discharges at sites are also calculated using bed roughness(Manning's n) and slope in straight sections with uniform flow conditions. Stream power is derived from the discharges calculated in this manner. The combination of stream power and recurrence intervals explains the occurrence of most vegetation types occurring on the banks, except for one type: Afromontane Forest. This type is probably more dependent on other factors, such as protection from fire and the depth of the groundwater table.

Analysis on the Cause of Mayang Stream’s Mountain Torrent Disaster of the Typhoon Meranti (201614)

Based on the flood area hydrodynamic model, this paper backs the analysis of the risk warning point of the Mayang Stream in the typical flood process, to determine the disaster-caused critical precipitation and the corresponding flood risk map at different depths of submergence. The result is used as the mountain torrent disaster monitoring and warning indicators and risk assessment of the Mayang Stream. Then based on the flood risk warning service system of small and middle rivers of Fujian Province, the risk warning service of mountain torrent disaster is developed during the impact time of Meranti in 2016. After the process of typhoon, the mountain torrent caused by Meranti was back analyzed by using the decided flood area model, then compared with the results of filed investigation to verify the accuracy of the disaster-caused critical precipitation forecast and the effect of monitoring and early warning services. The result shows that the cause of Mayang Stream’s mountain torrent disaster of the typhoon Meranti is the heavy rainfall and the strong wind. The highest mountain torrent disaster was forecasted by the refine precipitation based on the disaster-caused critical rainfall of the Mayang Stream. The simulated flood scenarios and the field trip’s results were basically matched in upstream and not matched in the downstream. The post-mountain simulation assessment also showed that the flood inundation range basically matched with reality, but the flood process was biased. The reason was that in addition to the differences between the surface rainfall forecast and the real situation, many actual situations cannot be ignored. For example, Meranti caused serious damage to trees, increased river blockages, resulting in changes in flood inundation time and depth, affecting the flood process. It showed the tourism development would cause the river way blocking and increase the risk of flood. In order to prevent and reduce the flood disasters accurately and effectively, the flood risk forecast and the disaster-caused facts should be considered at the same time.

Exploration of Sponge System Design in Wetland Parks Based on Rainwater and Flood Control: A Case Study of Southern Anhui Province

Based on the background that wetland resources in China are under threat and urgently need to be protected,a series of rainwater and flood problems caused by urban construction is analyzed comprehensively,and the design and planning methods of wetland parks in response to rainwater and flood disasters caused by floods and heavy rainfall are explored.Southern Anhui with complex and variable terrain and frequent rainfall and flood disasters is selected as the research area,with Xuanzhou District of Xuancheng City as the main research object.The relationship between municipal drainage of urban park and water conservancy drainage is investigated from different sample selection,design samples,and design flow rates.Based on literature review and model building methods,an urban storm flood model suitable for typical wetland parks in southern Anhui is constructed after processing the survey data using Arc GIS,SWMM(storm water management model).On this basis,a methodology and principles for designing a sponge system of wetland park based on rainwater and flood control are proposed,including technical measures such as rainwater collection,retention,and purification.This paper provides certain research results in design schemes,effect evaluations,ecological and social benefits,and useful suggestions and solutions for urban stormwater management and resilience development.

基于机器学习降雨动态时空特征识别山丘区小流域洪水预报方法研究

山丘区洪水产汇流速度快,破坏力强,预报难度大。如何进一步提高山丘区洪水预报的准确性和预见期,是当前亟待解决的主要问题。针对该问题,本文基于机器学习技术,创新性地提出了一种洪水预报的新方法。该方法通过识别与当前降雨动态时空特征最相似的历史降雨洪水过程,“借古喻今”进行洪水预报。结果表明,在人为影响小、流域面积在600 km^(2)左右的山丘区小流域,该方法预报洪峰流量平均误差为8.33%,洪量平均误差为14.27%,峰现时间平均误差1 h,均达到了洪水预报精度要求。区别于传统的洪水预报方法,该方法从整场降雨发展趋势的角度上预报山洪,更有针对性,为山丘区小流域洪水预报提供了新思路,为“三道防线”数据深度挖掘,防洪“四预”智能化水平提升提供有力技术支撑。

考虑泥沙因子的四川省山洪风险评价研究

近年来,山洪灾害频发高发,为进一步提高山洪灾害预警防控水平,提出将泥沙因子纳入山洪风险评价中。以四川省为例,从洪水危险性、脆弱性和防灾能力3个方面选取12个山洪风险指标,运用层次分析法构建山洪风险评估指标体系,分别建立了不考虑泥沙因子和考虑泥沙因子的山洪灾害风险评估模型。结果表明:泥沙因子对山洪危险性和风险性有较大影响。不考虑泥沙因子的模型将低估山洪高风险、较高风险区域和中等风险区面积,而高估低风险、较低风险区域面积。研究成果可为山洪风险评价与灾害预防提供参考。

基于AHP-EWM的流域山洪风险综合评价研究

为合理评估并量化小流域山洪灾害风险,结合小流域山洪特点,从危险性、脆弱性和防灾减灾3个方面构建小流域山洪风险评价指标体系。采用层次分析法(AHP)、熵权法(EWM)分别确定指标的主、客观权重,结合博弈集结模型确定指标综合权重,最后基于幂指数法得到小流域山洪风险综合评价值,从而确定综合风险等级。以湖北省随州市柳林镇8·12山洪为例开展小流域山洪风险评价,最终得出其综合评价值为0.634 9,为较高风险,与柳林镇实际情况一致。该研究结果可为小流域山洪灾害预防提供理论指导,为灾害的应急救援提供决策支持。

山区县域洪水预测研究--以阳朔县为例

山区县域的洪水灾害是我国防洪减灾体系中的薄弱环节。为提升洪水预测的准确性,以桂林阳朔县为例,基于HEC-HMS和InfoWorksICM模拟平台,构建田家河流域的水文水动力模型。利用2017—2022年间多场洪水数据对模型进行率定和验证。在此基础上,根据田家河与漓江的洪峰遭遇,预测12种不同洪水重现期组合的情景工况,并对每种情景下的淹没耕地面积、村庄数量、旧城区淹没面积以及新城区淹没面积进行统计和分析。研究结果表明:(1)遇龙河沿岸受灾情况受其上游暴雨洪水的影响,田家河流域洪水重现期TTJH=50a时,淹没耕地面积将超过8.15km2,沿途受影响村庄超过27个;(2)旧城区主要受漓江过境洪水的影响,漓江洪水重现期TLJ=20a时,漓江水位漫堤行洪,西街将处于1~2m的水深之中;(3)新城区对田家河流域及漓江洪水都表现出较高的敏感性,当洪水等级超过TTJH=10a且TLJ=20a或者TTJH=20a且TLJ=10a时,新城区将会遭遇较严重的洪灾。研究结果可为山区县域洪水预测提供参考。

岩溶山区小流域水库工程设计洪水计算——以WL水库工程为例

为科学合理确定岩溶山区小流域水库工程设计洪水,以WL水库为研究对象,考虑坝址以上伏流区、明流区分布,按全面积法、分块叠加法分别计算设计洪水,经综合比较确定坝址推荐设计洪水过程。结果表明,分块叠加法计算的设计洪水成果与坝址下游历史洪水调查成果较接近,能反映伏流区对坝址洪水调节的实际情况,并与区域已有洪水成果协调,为该工程坝址推荐设计洪水成果。本研究成果对开展区域岩溶山区水库设计洪水计算工作有一定的借鉴意义。