Development of a flood forecasting system using IFAS: a case study of scarcely gauged Jhelum and Chenab river basins

Development of a well-calibrated, distributed hydrological model for flood forecasting based on rainfall and snowmelt is quite challenging, especially when in situ data is limited or unavailable. This paper presents the study carried out to parameterise the Integrated Flood Analysis System (IFAS) model for the trans-boundary, scarcely gauged catchments of Jhelum and Chenab rivers in Pakistan. Rainfall-runoff analysis was performed with a two-layered tank configuration, integrating snowmelt and dam and barrage operation from the very upstream in India to Trimmu Barrage in Pakistan. A grid size of 5?×?5 km was considered. Global map topography, land cover and soil data was utilised. The model was tested considering different magnitudes of floods of the years 2014, 2015 and 2017. The results showed that the satellite rainfall product, i.e. Global Satellite Mapping of Precipitation (GSMaP-NRT), underestimated the rainfall volume, compared to the ground-gauged rainfall. The GSMaP-IF correction method showed poor performance owing to the lack of ground observatory rainfall data for correcting the trans-boundary part of the basin. The GSMaP-Type1 correction method showed good results, except for the confluence point where complex flow conditions were not properly reproduced by the model. In addition, the incorporation of dam and barrages in the model improved the simulated flow results. It is concluded that the satellite rainfall estimates must be corrected to improve the results. Snowmelt module estimated the snowmelt contribution as 3 to 7% and 4 to 23% of the average daily discharge during the monsoon season at Mangla Dam and Marala Barrage, respectively, during 2014 and 2015. This study assessed various correction methods and concluded that the model and methodology used in the study functioned well with suitable precipitation.     

Public perception of flood hazard and flood risk in Iceland: a case study in a watershed prone to ice-jam floods

Understanding and improving the public perception has become an important element in the management of flood risk worldwide. In Iceland, studying perception of flood hazard and flood risk is, however, in its early stages. This paper presents a case study on the public perception of flood hazard and flood risk in an Icelandic town prone to ice-jam floods. Awareness of the population regarding historical inundations, self estimation of flood risk and worry is considered. The factual knowledge of the residents is deconstructed in flood hazard parameters accessible to the lay population: number of events, dates, genesis and boundaries. The performance of the respondents is rated for each parameter and the influence of several predictors evaluated. The research shows three significant patterns: there is poor awareness and little worry about historical inundations in the area; experience of the past flooding events in town is the most effective source of knowledge; awareness, risk estimation and worry are not correlated.     

Reconstruction and post-event analysis of a flash flood in a small ungauged basin: a case study in Slovak territory

Flash floods are one of the major natural hazards occurring in small streams with a negative effect on the country as well as on human lives. Heavy rainfall occurred on July 20, 2014 and July 21, 2014 and caused severe surface water flooding and a flash flood in the Malá Fatra National Park (Slovakia). The most affected was Vrátna Valley with the Varínka stream. This study presents a reconstruction and post-event analysis of a flash flood on small ungauged basin located in this protected area of Slovakia. The reconstruction included hydraulic terrain measurements on estimating the flood’s culmination and documenting the flood’s development. The measurements were taken at three cross sections of the Varínka stream. This paper is focused mainly on post-event analysis of the Varínka stream in two profiles: Strá?a (gauged profile) and Tiesňavy (ungauged cross section). Subsequently, the extremeness of the flash flood was preliminary evaluated. Results of the post-event analysis showed that the July 2014 flood was not the highest flood in this area despite its catastrophic consequences. By studying historical materials, we came to the conclusion that in the past (e.g. in 1848 or 1939) some devastating floods in this area had occurred, which had disastrous consequences for the population. The second part of the study is focused on comparing this flash flood with three major floods which have occurred in Slovak territory since 1998. The first flood occurred on the 20th of July, 1998 on the Malá Svinka stream, and the two others are floods which occurred on the 7th of June, 2011 in the Small Carpathian Mountains: on the Gidra stream in Píla village and on the Parná stream in Horné Ore?any village. Such comparison of flash floods from different geographical regions and different rainfall events can provide comprehensive information about their regimes, threats and disastrous effects.     

流域不同地质生态环境中水体碳酸酐酶活性特征——以桂江流域为例

在对桂江流域进行考察时,选取了流域地质类型不同、人类活动程度不一的6条支流以及干流的水体为研究对象,研究比较了流域不同生态环境下水体中的碳酸酐酶(CA)活性、游离CO2浓度和HCO3-浓度,并对比了流域内部分区域的归一化植被指数(NDVI)数据,获得如下结果:(1)证实水体中具有CA活性,且其活性与游离CO2浓度呈负相关,与HCO3-浓度呈正相关;(2)大量的人类活动加剧流域生态环境恶化,造成植被覆盖率降低,使河流水体中的CA活性降低,HCO3-浓度降低,表明CA对岩溶作用具有不可忽视的影响;(3)流域地质类型会影响水体中CA活性,在人类活动程度相似的情况下,岩溶区水体中的CA活性高于非岩溶区。总之,在进行流域碳汇潜力调查研究时,必须综合考虑人类活动、生态环境和地质类型等因素的影响,进行科学分段调查研究与计算。CA所引起的生物岩溶作用不容忽视,其对流域碳汇的潜在贡献值得深入研究。      

Scale,governance and the management of river basins: A case study from Central Iran

Aquatic socio-ecological systems show pervasive cross-scale interactions and problems of fit between ecosystems and institutions. Nested bio-hydrological processes within river basins are prone to third-party impacts, and equitable/sustainable management of water resources requires adequate governance patterns that both cover relevant scalar levels and handle cross-scale interactions. This paper provides the example of the Zayandeh Rud basin, in central Iran, and describes the historical evolution of water use at three different nested scales. It shows how the gradual overallocation of water resources (basin closure) and the manipulation of the hydrological cycle by the state and other actors have resulted in a constant spatial and social redistribution of water use and associated benefits and costs. State-centered modes of governance characterized by the priority to large-scale infrastructure, vested political and financial interests, lack of attention to local processes and hydrological interconnectedness, and the neglect of environmental degradation, must give way to forms of comanagement that better articulate the different levels of control and governance.     

Evaluation of the consistency of landslide susceptibility mapping: a case study from the Kankai watershed in east Nepal

GIS-based landslide susceptibility maps for the Kankai watershed in east Nepal are developed using the frequency ratio method and the multiple linear regression technique. The maps are derived from comparing observed landslides with possible causative factors: slope angle, slope aspect, slope curvature, relative relief, distance from drainage, land use, geology, distance from faults and mean annual rainfall. The consistency of the maps is evaluated using landslide density analysis, success rate analysis and spatially agreed area approach. The first two analyses produce almost identical quantitative results, whereas the last approach is able to reveal spatial differences between the maps and also to improve predictions in the agreed high landslide-susceptible area.     

A quantitative analysis for geomorphic indices of longitudinal river profile: a case study of the Choushui River,Central Taiwan

Due to the plate movement is considerably slow, the human history record is too short to register landscape change for such a long time scale. However, longitudinal river profile can display watershed landscape characteristics. Therefore, this paper applies a quantitative analysis of geomorphic indices coupled with some mathematical models for the Choushui River and its six tributaries, including the gradient index and slope–area relationship. The abnormally high SL and SL/k values indicated that a decreasing trend from lower- to mid-stream areas and south Lishan fault was higher than north Lishan fault on the upstream areas, and the result of slope–area relationship also indicated that the regression line of the upper and lower steam exhibit an obvious right-shift nearby Lishan fault, could be explained by geodynamic models of active deformation in Taiwan area. This study also found that the abnormally high values of SL/k were affected by river and fault intersecting to form a high angle or perpendicular and the abnormally low values of SL/k were affected by river along with a fault or form a low angle, but the channel of Junda River along with Lishan fault is opposite. Based on quantitative results of these geomorphology indices, this study suggests that the important factor influencing landscape of the Choushui River watershed is tectonic uplift.     

基于FloodArea模型的小流域山洪灾害临界雨量阈值初探

针对缺乏水位流量资料的山区小流域地区山洪临界雨量难以确定的问题,以四川省南江河上游流域作为研究区域,基于德国Geomer公司开发的二维非恒定流水动力模型"FloodArea ",利用流域逐时降雨资料,地形高程数据以及土地利用数据,重现南江" 6·28"山洪暴发的动态演进过程,对模拟得到的逐时淹没深度与1~24 h累积流域面雨量求相关,选取预警点淹没深度与累积面雨量的相关系数最高的时效作为预警点致灾临界雨量阈值的预报时效,通过建立预警点淹没深度与预报时效累积面雨量的回归方程,从而获取预警点不同风险等级的临界雨量阈值。结果表明：FloodArea模型能够较好地呈现出此次典型山洪的暴发过程,通过对不同地势预警点临界雨量阈值的对比,最终选取地势较低,位于河流汇口地带、风险等级较高的上两九义校作为南江河上游流域山洪风险预警点。     

Comparative study of flash flood in ungauged watershed with special emphasizing on rough set theory for handling the missing hydrological values

Natural Hazards - Prediction of the flash floods in ungauged or poorly gauging watershed is one of the challenging tasks in the field of hydrology and needs implication of advanced techniques to...     

Assessing flood disaster impacts in agriculture under climate change in the river basins of Southeast Asia

Natural Hazards - This study focused on flood damage assessment for future floods under the impact of climate change. Four river basins of Southeast Asia were selected for the study. They included...     

平原河网地区汇水区的划分方法——以上海市为例

借助DEM提取汇水区是分布式水文模型计算和面源污染计算的前提条件.在平坦地区直接使用DEM提取出的水系、汇水区边界与现实情况差异很大.针对现有汇水区提取方法存在的问题,在RIDEM模型的基础上提出了一种平原河网地区汇水区划分的方法,该方法通过将道路、建筑物、水系、沟渠、坑塘等影响径流途径的地物要素融合进DEM,达到细化...     

Impact of land use change on groundwater quality in a typical karst watershed of southwest China: a case study of the Xiaojiang watershed,Yunnan Province

The impact of land-use change on the quality of groundwater in the Xiaotjiang watershed, China was assessed for the period 1982–2004. Groundwater samples were collected from 30 monitoring points across the watershed, and were representative of the various changes, determined by remote sensing and geographical information systems. The results indicate that 610 km² (60% of the total watershed area) were subject to land-use change during the period. The most important changes were the conversion of 135 km² of forested land to cultivated land, and 211 km² of unused land to cultivated land. The main impact was ascribed to diffuse pollution from fertilizers applied to newly cultivated land, and from building development. Overall the groundwater pH value was significantly increased, as were the concentrations of ions , , , , and Cl⁻ in groundwater whilst the concentrations of Ca²⁺ and declined. More precisely, in the regions where forested land and unused land were converted into cultivated land, the pH value and the concentrations of Mg²⁺, , , , , Cl⁻ increased whilst the concentrations of Ca²⁺ and declined. However in the region where cultivated land was converted into construction land, the pH value and the concentrations of Ca²⁺, Mg²⁺, , , , , , Cl⁻ increased.

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Résumé  L’impact des changements de l’utilisation du territoire sur la qualité de l’eau souterraine dans le bassin versant de Xiaojiang, en Chine, a été évalué de 1982 à 2004. Des échantillons d’eau souterraine ont été récoltés à partir de 30 points d’observation éparpillés sur le bassin, représentant les divers changements déterminés par télédétection et système d’information géographique. Les résultats indiquent que 610 km² (soit 60% de la surface du bassin) ont été sujets à des modifications de l’utilisation du territoire sur cette période. Les changements les plus importants furent la conversion de 135 km² de forêt et 211 km² de terres inutilisées en terres cultivées. Le principal impact est attribué à la pollution diffuse des engrais utilisés en agriculture et pour les batiments. De manière générale le pH de l’eau souterraine a augmenté significativement, ainsi que les concentrations des ions , , , , et Cl⁻, tandis que les concentration en Ca²⁺ et ont diminué. Plus précisément dans les régions transformées en terres cultivées, la valeur du pH et les concentrations en Mg²⁺, , , , , Cl⁻ ont augmenté tandis que les concentrations en Ca²⁺ et ont diminué. Toutefois dans les régions cultivées converties en zones de construction, le pH et les concentrations en Ca²⁺, Mg²⁺, , , , , , Cl⁻ ont augmenté.

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Resumen  El impacto del cambio en uso de la tierra en la calidad del agua en la cuenca Xiaojiang, China fue evaluado para el periodo 1982–2004. Muestras de agua subterránea fueron tomadas de 30 puntos de monitoreo a través de la cuenca, y fueron representativas de los múltiples cambios, determinados por sensores remotos y sistemas de información geográfica. Los resultados indican que 610 km² (60% del área total de la cuenca) estaban sujetos a cambios de uso de la tierra durante el periodo estudiado. Los cambios más importantes fueron la conversión de 135 km² de bosques a tierra cultivada, y 211 km² de tierra sin uso (ociosa) a tierra cultivada. El impacto principal fue causado por contaminación difusa de fertilizantes aplicados a la tierra recientemente cultivada, y a desarrollo de construcciones. En general el pH en agua subterránea creció significantemente, al igual que las concentraciones de los iones , , , , y Cl⁻ en agua subterránea mientras que las concentraciones de Ca²⁺ y decrecieron. Mas precisamente, en las regiones donde bosque y tierra ociosa fueron convertidas en tierra cultivada, el valor de pH y las concentraciones de Mg²⁺, , , , , Cl⁻ crecieron mientras las concentraciones de Ca²⁺ y decrecieron. Sin embargo en la región donde tierra cultivada fue convertida en construcciones, el valor de pH y las concentraciones de Ca²⁺, Mg²⁺, , , , , , Cl⁻ crecieron.

     

Development of roughness updating based on artificial neural network in a river hydraulic model for flash flood forecasting

Flood is the worst weather-related hazard in Taiwan because of steep terrain and storm. The tropical storm often results in disastrous flash flood. To provide reliable forecast of water stages in rivers is indispensable for proper actions in the emergency response during flood. The river hydraulic model based on dynamic wave theory using an implicit finite-difference method is developed with river roughness updating for flash flood forecast. The artificial neural network (ANN) is employed to update the roughness of rivers in accordance with the observed river stages at each time-step of the flood routing process. Several typhoon events at Tamsui River are utilized to evaluate the accuracy of flood forecasting. The results present the adaptive n-values of roughness for river hydraulic model that can provide a better flow state for subsequent forecasting at significant locations and longitudinal profiles along rivers.     

贵州乌江南源上游流域不同岩溶地貌单元的流量衰减分析

选取云南高原向贵州高原过渡地带上的乌江南源——贵州省三岔河上游流域作为研究对象,分别提取其流域内的花渔洞地下河流域与三塘地下河流域的地形指标,分析两者的流量衰减现状,并探讨了岩溶地表形态和岩溶含水介质结构之间的关系。结果显示：（1）花渔洞地下河流域的平均起伏度为73.2 m,可分为高起伏度的Ⅰ区（均值122 m）和低起伏度的Ⅱ区（均值64 m）两个区,其分别占整个流域面积的14.9%和85.1%;三塘地下河流域的平均起伏度为87.6 m,可分为高起伏度的Ⅰ区（均值106 m）、中起伏度的Ⅱ区（均值81 m）和低起伏度的Ⅲ区（均值48 m）三个区,其分别占流域面积的40.2%,49.7%和10.1%;（2）花渔洞地下河流域各阶段的衰减系数为0.000 3,0.000 1,0.000 06（0.5 h）-1,总蓄水量达2 199.356×104 m3,各亚动态蓄水量分别占总蓄水量的0.1%,9.9%、90.0%;三塘地下河流域各阶段的衰减系数为0.001、0.000 3、0.000 1（0.5 h）-1,总蓄水量为2 310.902×104 m3,各亚动态蓄水量分别占总蓄水量的9.4%、30.8%、59.8%。这表明地面起伏度和衰减动态之间可能存在着关联性,即高起伏度对应岩溶发育强烈的管道流,低起伏度对应导水通道较小的裂隙、溶隙等含水层。     

Age of river basins in Guadeloupe impacting chemical weathering rates and land use

The Lesser Antilles have very high chemical weathering rates, with values that can reach 1290 t/km²/a. The tropical environment induces high precipitation rates, high temperature, dense vegetation, with sharp relief and thick soils. Because of volcanic activity, frequent pyroclastic flows produce very erodible and porous materials. In addition, agriculture induces important land use changes which replace existing native forest cover with banana and sugar cane plantations. Their surface can cover as much as 40% of the total area of a river basin. The aim of this study is to identify key parameters, either natural or anthropogenic, that control chemical weathering rates. Among the combined impact of all parameters (climate, runoff, slopes, vegetation etc.), basin age seems to be the control parameter: the younger the basin, the higher the weathering rate. A correlation between the chemical weathering rate and the basin age suggests that young volcanic rocks are more easily weathered than old ones: young fresh material is easily mobilized by erosion, while for older rocks with thick soil covers, chemical rates are much lower. A combined effect between the higher erodibility and a higher climate erosivity of the younger relief could be observed. Moreover, a correlation between banana plantations and the chemical weathering rates that can be explained by an increase of infiltration, due to stem flow processes is shown here. Banana plantations also have a correlation with the basin age, older basins being more favorable terrains for cultivation.