Floodplain Management in Urban Developing Areas. Part II. GIS-Based Flood Analysis and Urban Growth Modelling

In Part I of this article the very dynamic nature of floodplain management was discussed and the need for modelling the urban growth processes and formulating scenarios of urban development was emphasised. In this second part, the use of Geographic Information Systems (GIS) for addressing those problems is presented. GIS have been recognised as a powerful means to integrate and analyse data from various sources in the context of comprehensive floodplain management. Adequate information and prediction capability is vital to evaluate alternative scenarios for flood mitigation policies and to improve decision making processes associated with flood management. A framework for the comprehensive evaluation of flood hazard management policies is also addressed in this article. This comprehensive approach to flood problems is more than an attitude or a philosophical starting point. It makes use of specific technological tools conceived to be used by different actors, some of them being nonexperts in flood analysis. These tools, based on GIS, are very appropriate for a participatory approach to flood policy formulation and floodplain management because they help communicating with the public in a scientifically correct and yet rather simple manner.     

Floodplain Management in Urban Developing Areas. Part I. Urban Growth Scenarios and Land-Use Controls

Some of the most critical flood problems occur in urban areas where values at risk are higher and damages tend to be heavier. Fast urban developing regions raise very specific problems because of the unsteady situation of these regions in terms of catchment land-use and urban encroachment. A realistic approach to flood management in these situations requires the consideration of urban growth scenarios and the simulation of the corresponding flood conditions. Coastal towns are frequently located in floodplains and are subject to flood hazard. This is the case for many coastal areas in Southern Europe that are still developing fast due to migration of the population to these areas. In such cases, flood management cannot be dissociated from land-use management, and non-structural measures for flood control can play a crucial role. It is important to make an ex-post evaluation of these types of measures in areas where they have been adopted. These issues are addressed in two Portuguese catchments, representative of urban growth and related to flood problems in Portugal and other Southern European regions. The Laje catchment is used for the ex-post evaluation of nonstructural measures, and the Livramento catchment is used for the modelling of urban growth scenarios. Quantitative results and policy recommendations are presented based on these two case-studies. Floodplain management is better done with GIS, especially if it is linked to hydrologic and hydraulic modelling capabilities. The use of GIS for conducting these studies is presented in Part II of this article.     

Modelling floodplain inundation on a regulated river: integrating GIS,remote sensing and hydrological models

The lower River Murray in South Australia is highly regulated through weirs and water extraction for irrigation. Management of the river for environmental purposes requires an understanding of the extent of floodplain inundation from various flows and weir manipulations. This study aimed to produce a floodplain inundation model for the 600 km long and 1–5 km wide portion of the River Murray in South Australia from the New South Wales border to Lake Alexandrina. The model was developed using a Geographical Information System (GIS), remote sensing and hydrological modelling. Flood inundation extents were monitored from Landsat satellite imagery for a range of flows, interpolated to model flood growth patterns and linked to a hydrological model of the river. The resulting model can be analysed for flows ranging from minimum flow to a 1‐in‐13‐year flood event for any month and weir configuration and has been independently tested using aerial photography to an accuracy of approximately 15% underestimate. The results have proven the approach for determining flood inundation over a large area at approximately one‐tenth of the cost of detailed elevation and hydrodynamic modelling. The GIS model allows prediction of impacts on infrastructure, wetlands and floodplain vegetation, allowing quantitative analysis of flood extent to be used as an input into the management decision process. Copyright © 2005 John Wiley & Sons, Ltd.     

洪水避难分析系统的研究开发及其应用

随着经济社会快速发展,洪水高风险区中人口资产密度增大,受全球气候变化影响,台风、极端暴雨等形成的洪水灾害给高风险区的人员资产带来更大的威胁。危机时刻,如何更为有效、有序地组织灾区民众的避难转移是减少伤亡和损失的重要手段。本文从水文水力学、灾害学与地理信息科学等交叉视角,利用二维洪水仿真模型进行洪水演进模拟分析,对需避难转移人员及其空间分布特征进行识别;提出安置区的选择规划及优化匹配方法;建立最优转移路径分析模型及道路拥堵计算模型;在GIS平台上集成相关模型方法,开发洪水避难分析系统。在荆江分洪区进行了实例应用研究,建立了荆江分洪区的洪水模拟分析模型,用1954年分洪的实况洪水进行分洪区的洪水演进模拟分析,根据分析结果将分洪区划分为危险重灾区、深水重灾区和进洪轻灾区3个危险区域,利用荆江分洪区2014年分洪预案进行1954年实况分洪情景下的避难转移模拟分析,提出了基于洪水演进特征的分批次转移的改进优化方案。应用实例研究表明,本文建立的模型方法和相关系统具有较好的实用价值,可以为分蓄洪区等区域洪水避难方案的制定提供分析优化手段。     

Evaluating Flood Hazard for Land-Use Planning in Greater Dhaka of Bangladesh Using Remote Sensing and GIS Techniques

Floods are a common feature in rapidly urbanizing Dhaka and its adjoining areas. Though Greater Dhaka experiences flood almost in every year, flood management policies are mostly based on structural options including flood walls, dykes, embankments etc. Many shortcomings of the existing flood management systems are reported in numerous literatures. The objective of this paper is to assess flood hazard in Greater Dhaka for the historical flood event of 1998 using Synthetic Aperture Radar (SAR) data with GIS data. Flood-affected frequency and flood depth calculated from the multi-date SAR imageries were used as hydrologic parameters. Elevation heights, land cover classification, geomorphic division and drainage network data generated from optical remote sensing and analogue maps were used through GIS approach. Using a ranking matrix in three dimensional multiplication mode, flood hazard was assessed. All possible combination of flood hazard maps was prepared using land-cover, geomorphology and elevation heights for flood-affected frequency and floodwater depth. Using two hazard maps which produced the highest congruence for flood frequency and flood depth, a new flood hazard map was developed by considering the interactive effect of flood-affected frequency and floodwater depth, simultaneously. This new hazard map can provide more safety for flood countermeasures because pixels belonging to higher hazard degrees were increased due to the consideration of higher degrees of ranks. The estimation of flood hazard areas revealed that a major portion of Greater Dhaka comprised moderate to very high hazard zone. Only a little portion (8.04%) was found to be the least vulnerable to potential flood hazard. Conversely, 28.70% of Greater Dhaka was found within very high hazard zone. Based on this study, comprehensive flood hazard management strategies for land use planning decision were proposed for the efficient management of future flood disasters.     

FLOOD INUNDATION MAPPING FOR INTEGRATED FLOODPLAIN MANAGEMENT: UPPER MISSISSIPPI RIVER SYSTEM

Natural hydrogeomorphic characteristics and hydrologic alterations are important ecological drivers, and hydrology is also a common ecological, flood control and navigation system indicator. Hydrologic characteristics change dramatically from one end of the Upper Mississippi River System to the other, and hydraulic characteristics also differ spatially across the river channels and floodplain in response to dams, levees and diversions. Low flow surface water spatial change in response to navigation and flood control has been well known for many years, but little information was available on the spatial distribution of frequent floods. The flow frequency data presented here were developed to better estimate contemporary floods after historic flooding in 1993. Flood stage estimates are enhanced in GIS to help quantify and map potential floodplain inundation for more than 1000 river miles on the Upper Mississippi and Illinois Rivers. Potential flood inundation is mapped for the 50% to 0.2% annual exceedance probability flood stage (i.e. 2‐ to 500‐year expected recurrence interval flood) and also for alternative floodplain management scenarios within the existing flood protection infrastructure. Our analysis documents: (i) impoundment effects, (ii) a hydrologic gradient within the navigation pools that creates repeating patterns of riverine, backwater and impounded aquatic habitat conditions, (iii) potential floodplain inundation patterns for over 2 million acres and (iv) several integrated floodplain management scenarios. Extreme flood events are more common in recent decades, and they are expected to continue to occur at greater frequency in response to climate change. Floodplain managers can use the results presented here to help optimize land management and flood damage reduction on the Upper Mississippi River System. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.     

Floodplain management strategies for flood attenuation in the river Po

This paper analyses the effects of different floodplain management policies on flood hazard using a 350 km reach of the river Po (Italy) as a case study. The river Po is the longest Italian river, and the largest in terms of streamflow. The middle‐lower Po flows East some 350 km in the Pianura Padana (Po Valley), a very important agricultural region and industrial heart of Northern Italy. This portion of the river consists of a main channel (200–500 m wide) and a floodplain (overall width from 200 m to 5 km) confined by two continuous artificial embankments. Floodplains are densely cultivated, and a significant portion of these areas is protected against frequent flooding by a system of minor dykes, which impacts significantly the hydraulic behaviour of the middle‐lower Po during major flood events. This study aims at investigating the effects of the adoption of different floodplain management strategies (e.g. raising, lowering or removing the minor dyke system) on the hydrodynamics of the middle‐lower Po and, in particular, on flood‐risk mitigation. This is a crucial task for institutions and public bodies in charge of formulating robust flood risk management strategies for the river Po. Furthermore, the results of this study are of interest for other European water‐related public bodies managing large river basins, in the light of the recent European Directive 2007/60/EC on the assessment and management of flood risks. The analysis is performed by means of a quasi‐2D hydraulic model, which has been developed on the basis of a laser‐scanning DTM and a large amount of calibration data recorded during the significant flood event of October 2000. Copyright © 2010 John Wiley & Sons, Ltd.     

黄河下游宽滩区滞洪沉沙功能与减灾效应二维评价模型及其应用

黄河下游宽滩区既是大洪水行洪滞洪沉沙的通道,又是滩区群众赖以生存和发展的家园,如何合理运用宽滩区是长期备受关注和争议的话题。本文在水沙统筹、空间统筹和时间统筹原则的指导下,建立了黄河下游宽滩区滞洪沉沙功能与减灾效应二维评价指标体系,构建了基于Pareto最优解的黄河下游宽滩区滞洪沉沙功能与减灾效应二维评价模型,利用1958、1982、1992和1996年4场洪水实测资料,对该模型的合理性进行了验证。应用上述模型对黄河下游宽滩区不同运用方式的12组二维数学模型计算方案进行了评价,结果表明,洪水量级对减灾效应影响显著;相同洪水条件下设防护堤并控制闸门运用(有闸)或分区运用(5滩、10滩)方案能在滞洪沉沙功能和减灾效应之间取得更好的平衡,可作为未来滩区优化运用的决策参考。     

Dynamics of river fish populations in response to hydrological conditions: a simulation study

Increasing multi‐sectoral demands on water resources have led to water abstraction and transfer activities, and the construction of dams and embankments that have significantly altered the flood regimes of rivers throughout the world resulting in the loss of fish production and biodiversity. The current emphasis on sustainable development and biodiversity conservation is leading efforts to mitigate these impacts by means of interventions such as the release of artificial floods downstream of dams and the manipulation of water levels within impounded floodplains. Whilst much work has been done to determine the hydrological requirements for the maintenance of salmonid populations, few equivalent studies are available from which to develop criteria for the management of hydrological regimes for fishes and fisheries in large floodplain–river systems such as the Mekong. The population dynamics of fish in such rivers are believed to respond to hydrological conditions in a density‐dependent manner. An age‐structured population dynamics model incorporating sub‐models describing density‐dependent growth, mortality and recruitment was used to explore how hydrological conditions within a theoretical floodplain–river system affect the dynamics of a common floodplain–river fish species. Graphical summaries of the response of exploitable biomass to a range of different drawdown rates, dry and flood season areas and volumes, and flood season durations are presented under five different model assumptions concerning density‐dependent processes. Optimal flooding patterns are also described for the model species and theoretical river system. The patterns of predictions that emerge from the simulations provide guidelines for managing or manipulating hydrological conditions in river systems for both fixed and variable volume hydrological scenarios. As a general rule of thumb, exploitable biomass is maximized by minimizing the rate of drawdown and maximizing the flood duration and flood and dry season areas or volumes. However, experiences from dam and other hydraulic engineering projects suggest that these predictions should be treated with caution until we better understand the influence of hydrology on spawning behaviour, system primary production, and critical habitat availability. Copyright © 2004 John Wiley & Sons, Ltd.     

闽江上游生态环境改变对山洪过程的影响研究

山洪灾害易发地区一般处于江河上游的生态脆弱区和生态敏感地带,水土流失和生态退化加剧了灾害程度。选取闽江上游为研究区域,重点研究生态环境变化与山洪的耦合关系。以2013年闽江上游生态系统分类结果为本底数据,利用GIS技术,模拟退耕还林、矿山恢复、生态封育3种生态最优情景以及生态退化情景。采用HEC-HMS模型,基于设计暴雨资料计算不同生态情景下洪水过程,进而分析生态优化及生态退化条件对山洪过程的影响。由研究结果可得,生态类型优化对洪水削峰滞时作用显著,洪水峰值减小,洪水集中度减小、冲击力减弱,不易成灾;生态条件退化后,洪峰值增加,峰现时间提前。因此,改善易灾地区生态环境,调节径流能力,可有效提升抗御山洪灾害的能力,对于减少山洪灾害损失具有重要意义。     

MORPHOLOGICALLY RELATED INTEGRATIVE MANAGEMENT CONCEPT FOR RECONNECTING ABANDONED CHANNELS BASED ON AIRBORNE LiDAR DATA AND HABITAT MODELLING

Most of the large rivers are heavily degraded and lack near‐natural conditions due to high human pressure (agricultural use and settlements) especially on former inundation areas. Hence, it is rarely possible to ‘restore’ predisturbance conditions of rivers and their floodplains. Further, river or floodplain restoration programs are often based on type‐specific reference conditions. Those reference conditions are mainly determined on the basis of historical maps not giving any information of, for example, sediment supply, flood frequency and vegetation cover (density). Especially for improving the ecological status of rivers with abandoned channel features, key habitats for target fish species have to be restored by reconnecting floodplains and their secondary channel system. In addition, because of the necessity of improving the ecological status, there is growing interest in interdisciplinary river restoration techniques. Within the presented article, an integrative concept is derived based on Light Detection and Ranging measurements and numerical modelling with respect to river dynamics (hydrologic and morphological). Further habitat modelling, based on unsteady depth‐averaged two‐dimensional hydrodynamics, is applied with a focus on the mesounit scale. For testing the conceptual model, various river reaches at the Morava River were selected, featuring different morphological characteristics. It was found that the applied management concept allows considering the important issues of river dynamics (morphological/hydrologic) using a flow‐ and flood‐pulse approach for identifying bottlenecks of target species at the Morava River. The reconnection of abandoned channels will result in an increase of hydromorphological heterogeneity and/or woody debris within the study reach. This might be of high relevance for habitat features (e.g. backwater habitats) especially for flow pulses between low flow and mean flow and/or in reaches without abandoned channels between low‐flow and the bankfull stage. Copyright © 2012 John Wiley & Sons, Ltd.     

An Intelligent Decision Support System for Management of Floods

Integrating human knowledge with modeling tools, an intelligent decision support system (DSS) is developed to assist decision makers during different phases of flood management. The DSS is developed as a virtual planning tool and can address both engineering and non-engineering issues related to flood management. Different models (hydrodynamic, forecasting, and economic) that are part of the DSS share data and communicate with each other by providing feedback. The DSS is able to assist in: selecting suitable flood damage reduction options (using an expert system approach); forecasting floods (using artificial neural networks approach); modeling the operation of flood control structures; and describing the impacts (area flooded and damage) of floods in time and space. The proposed DSS is implemented for the Red River Basin in Manitoba, Canada. The results from the test application of DSS for 1997 flood in the Red River Basin are very promising. The DSS is able to predict the peak flows with 2% error and reveals that with revised operating rules the contribution of Assiniboine River to the flooding of Winnipeg city can be significantly reduced. The decision support environment allows a number of “what-if” type questions to be asked and answered, thus, multiple decisions can be tried without having to deal with the real life consequences.     

水库溃坝洪水风险图编制研究

采用水力学模型,对溃坝流量以及溃坝后下游各断面的淹没水深和淹没范围等水力风险要素进行计算,基于ArcGIS技术开发了江苏省句容市北山水库洪水风险图管理系统,对GIS空间属性表字段进行渲染,自动绘制出溃坝洪水淹没风险信息,为下游句容市区防洪减灾提供技术支持。     

黄河下游滩区实行分类管理的设想

随着小浪底水利工程的投入运用和黄河下游河道整治工程的逐步完善,以往笼统地将黄河下游滩区作为行洪河道管理的方式已不适应社会经济发展的要求。在全面调研分析的基础上,提出将黄河下游滩区按其功能分为3类进行建设与管理的新思路,即:Ⅰ类为行洪区、Ⅱ类为行滞洪区、Ⅲ类为集中居住区。为做好滩区的分类管理,现阶段应重点研究滩区的分类试点、滩区的补偿政策以及生产堤建设标准与管理政策等。     

黄河下游滩区洪水风险分析及减灾措施研究

黄河下游滩区洪水漫滩灾害频发,作为防洪非工程措施的洪水风险分析对于指导黄河下游滩区实施防洪减灾措施有着重要的意义。针对黄河下游滩区呈现“二级悬河”的不利局面及下游洪水泥沙含量大的特点,采用基于GIS的黄河下游二维水沙数学模型分量级计算相关洪水风险信息。根据洪水风险分析结果,制定滩区居民迁安救护方案,编制了不同量级洪水淹没下的滩区洪水风险图,增强滩区居民风险意识及应急避险撤退能力。提出了相关减灾应对措施,有着显著的防洪减灾效益。     

Hydrologic scaling for hydrogeomorphic floodplain mapping: Insights into human‐induced floodplain disconnectivity

Hydrogeomorphic approaches for floodplain modelling are valuable tools for water resource and flood hazard management and mapping, especially as the global availability and accuracy of terrain data increases. Digital terrain models implicitly contain information about floodplain landscape morphology that was produced by hydrologic processes over long time periods, as well as recent anthropogenic modifications to floodplain features and processes. The increased availability of terrain data and distributed hydrologic datasets provide an opportunity to develop hydrogeomorphic floodplain delineation models that can quickly be applied at large spatial scales. This research investigates the performance of a hydrogeomorphic floodplain model in two large urbanized and gauged river basins in the United States, the Susquehanna and the Wabash basins. The models were calibrated by a hydrologic data scaling technique, implemented through regression analyses of USGS peak flow data to estimate floodplain flow levels across multiple spatial scales. Floodplain model performance was assessed through comparison with 100‐year Federal Emergency Management Agency flood hazard maps. Results show that the hydrogeomorphic floodplain maps are generally consistent with standard flood maps, even when significantly and systematically varying scaling parameters within physically feasible ranges, with major differences that are likely due to infrastructure (levees, bridges, etc.) in highly urbanized areas and other locations where the geomorphic signature of fluvial processes has been altered. This study demonstrates the value of geomorphic information for large‐scale floodplain mapping and the potential use of hydrogeomorphic models for evaluating human‐made impacts to floodplain ecosystems and patterns of disconnectivity in urbanized catchments.     

黄河下游宽滩区不同运用模式滞洪沉沙效果试验

黄河下游宽滩区既是大洪水期行洪通道,具有滞洪、沉沙功能,又是180多万滩区人民居住场所。如何解决保证滩区群众生命财产安全与自然行滞洪、沉沙功能的发挥这一对矛盾,是治黄工作长期面临的难题之一。通过对比不同滩区运用模式下宽滩区洪水淹没范围、滞洪量和沉沙量,分析宽滩区不同运用模式对滩区滞洪沉沙效果的影响,以期为黄河下游河道治理和宽滩区安全建设提供有力科学依据。研究结果表明,两种洪水条件下无防护堤模式淹没范围均大于防护堤模式;中常洪水条件无防护堤模式滞洪量和沉沙量大于防护堤模式;大洪水条件无防护堤模式总滞洪量稍小于防护堤模式、沉沙量大于防护堤模式;两种洪水条件防护堤模式高村以下窄河段滩区漫滩状况均较无防护堤模式严重。     

Floodplain Mapping through Support Vector Machine and Optical/Infrared Images from Landsat 8 OLI/TIRS Sensors: Case Study from Varanasi

Floods are among the most destructive natural disasters causing huge loss to life and property. Any flood management strategy requires floodplain mapping through discrimination of the flood prone areas. The city of Varanasi or Benaras is believed to be the oldest continuously inhabited city of the world. This study aims to develop tools for mapping and discrimination of floodplain of river Ganga at Varanasi. During 2014 floods, the flooded areas were extracted through Normalized Difference Water Index (NDWI) and by Modified NDWI (MNDWI) using the NIR and SWIR bands separately from that of the Landsat 8 satellite imagery. The inundated areas were then identified through Support Vector Machines (SVMs) classification. The results reveal that the MNDWI images provide a better result for flood discrimination than the NDWI images. Ground based measurements for floodplain distance varied between 11 ± 5 m at Janki ghat (bank) and 80 ± 5 m at Asi ghat. The validation between measured and SVMs derived values indicate a strong positive correlation of 0.88 and a low value of Root Mean Square Error (RMSE) of 12.62. The t-test is suggestive of no significant difference between the observed and SVMs values at 95% confidence level, indicating a satisfactory performance of the SVMs for floodplain mapping using Landsat 8 imagery. Therefore, the methodology proposed in this study provides a novel and robust way for floodplain mapping and has potential applications in disaster management and mitigation in the flood affected regions.     

全国山洪灾害防治区划理论与实践初探

防治山洪灾害是我国山丘区可持续发展的一项重要工作.在掌握山洪灾害地域分异规律的基础上进行山洪灾害防治区划,对于科学地分析山洪灾害成因、时空分布差异特征和因地制宜地采取山洪灾害防治对策具有重要意义.在综合分析借鉴区划已有成果,特别是自然区划成果和掌握大量全国山洪灾害防治规划调查数据的基础上,从我国山洪灾害防治现状出发,提出全国山洪灾害防治区划等级系统.在此基础上以二级区为单元,借助GIS技术手段,统计分析各区山洪灾害发育特征.区划成果及山洪灾害发育特征分区统计分析为全国山洪灾害分区整治提供了科学根据.     

Uncertainty Estimation in Flood Inundation Mapping: An Application of Non‐parametric Bootstrapping

Disaster prevention planning is affected in a significant way by a lack of in‐depth understanding of the numerous uncertainties involved with flood delineation and related estimations. Currently, flood inundation extent is represented as a deterministic map without in‐depth consideration of the inherent uncertainties associated with variables such as precipitation, streamflow, topographic representation, modelling parameters and techniques, and geospatial operations. The motivation of this study is to estimate uncertainties in flood inundation mapping based on a non‐parametric bootstrapping method. The uncertainty is addressed through the application of non‐parametric bootstrap sampling to the hydrodynamic modelling software, HEC‐RAS, integrated with Geographic Information System (GIS). This approach was used to simulate different water levels and flow rates corresponding to different return periods from the available database. The study area was the Langat River Basin in Malaysia. The results revealed that the inundated land and infrastructure are subject to a flooding hazard of high‐frequency events and that the flood damage potential is increasing significantly for residential areas and valuable land‐use classes with higher return periods. The proposed methodology, as well as the study outcomes, of this paper could be beneficial to policymakers, water resources managers, insurance companies and other flood‐related stakeholders. Copyright © 2017 John Wiley & Sons, Ltd.