The importance of gully flow modelling to urban flood simulation

ABSTRACT

Urban flood simulation often ignores or simplifies the function of underground gully systems due to data and computational limitations. To discover the influence of gullies on urban flooding, a novel approach is proposed in this study, by fully-coupling a 1D gully flow model (GFM), a 1D sewer flow model (SFM), and a 2D overland flow model (OFM) to simultaneously simulate the flow exchanges between surface, gullies and sewer pipes. This fully-coupled approach is compared with a simplified approach which directly introduces surface water into sewer pipes without being via gullies. The validation results show that the fully-coupled approach considerably reduces the underestimation of flood extent by 27% compared with the simplified approach. Without considering the capacity of lateral tubes between gullies and sewer pipes, the simplified approach over-drains the surface water into sewer pipes. The modelling of gully flow is crucial for correctly evaluating the efficiency of drainage systems.     

长汀城市建设区洪水淹没风险研究

洪水淹没风险分析是进行城市防洪安全研究、合理布局城市建设用地的主要依据之一。本文基于GIS栅格数据空间分析技术,结合了传统淹没分析方法,使用长汀城市建设区地形和洪水水文数据资料,对研究区在10%、5%、2%三种频率下的洪水淹没风险进行了定量化分析,提出了城市建设用地控制原则,为城市规划中协调城市防洪安全与城市建设用地布局提供了有价值的参考。研究结果显示研究区洪水淹没风险总体上较高,城市已建设区洪水淹没风险高于其他区域。     

A new experiments-based methodology to define the stability threshold for any vehicle exposed to flooding

A vehicle exposed to flooding, after losing stability, becomes buoyant and may be washed away with potential injuries and fatalities. Such vehicles cause additional disruption to traffic that is already affected by flooding, which may lead to substantial indirect economic impact, especially in urban areas. Therefore, the analysis of the stability of vehicles exposed to flooding is important in order to make decisions to reduce damages and hazards. In this research, based on an experimental campaign that included a range of twelve car models, a new methodology to obtain the stability threshold for any real vehicle exposed to flooding is developed. A stability coefficient (SC_mod) is derived with which the vehicles can be sorted by stability against water flows and their stability functions may be determined. The experiments were conducted with three different model scales (1:14, 1:18 and 1:24) and involved analysis of both friction and buoyancy effects, which made this the most comprehensive research study to date. This methodology enables the definition of a stable area in the flow depth-velocity domain for any real vehicle. A tool is provided that decision-makers in the field of urban flood risk management can employ and after defining a design vehicle they can obtain its corresponding stability threshold.     

Application of surrogate artificial intelligent models for real‐time flood routing

Developing a robust flood forecasting and warning system (FFWS) is essential in flood‐prone areas. Hydrodynamic models, which are a major part of such systems, usually suffer from computational instabilities and long runtime problems, which are particularly important in real‐time applications. In this study, two artificial intelligence models, namely artificial neural network (ANN) and adaptive neuro‐fuzzy inference system (ANFIS), were used for flood routing in an FFWS in Madarsoo river basin, Iran. For this purpose, different rainfall patterns were transformed to run‐off hydrographs using the Hydrologic Engineering Center (HEC)‐1 hydrological model and routed along the river using HEC river analysis system RAS hydrodynamic model. Then, the simulated hydrographs with different lag times were used as inputs for training of ANN and ANFIS models to simulate flood hydrograph at the basin outlet. Results showed that the simulations obtained from ANN and ANFIS coincided with the results simulated by the HEC‐RAS, and application of such models is strongly suggested as a backup tool for flood routing in FFWSs.     

Validating a rapid assessment framework for screening surface water flood risk

This research evaluates performance of a rapid assessment framework for screening surface water flood risk in urban catchments. Recent advances in modelling have developed fast and computationally efficient cellular automata frameworks which demonstrate promising utility for increasing available evidence to support surface water management, however, questions remain regarding trade‐offs between accuracy and speed for practical application. This study evaluates performance of a rapid assessment framework by comparing results with outputs from an industry standard hydrodynamic model using a case study of St Neots in Cambridgeshire, UK. Results from the case study show that the rapid assessment framework is able to identify and prioritise areas of flood risk and outputs flood depths which correlate above 97% with the industry standard approach. In theory, this finding supports a simplified representation of catchments using cellular automata, and in practice presents an opportunity to apply the framework to develop evidence to support detailed modelling.     

非平原城市排洪规划技术路线研究

对非平原城市的防洪排涝规划进行了新的诠释和定义,通过对排洪规划重现期的选择、城区洪峰流量的推求方法、排洪规划方案的确定、城市内河水面线的计算以及排洪规划与城市竖向规划之间的配合等方面的研究,提出了非平原城市排洪规划的初步技术框架.     

Quantitative fault tree analysis for urban water infrastructure flooding

Flooding in urban areas can be caused by heavy rainfall, improper planning or component failures. Few studies have addressed quantitative contributions of different causes to urban flood probability. In this article, we apply probabilistic fault tree analysis for the first time to assess the probability of urban flooding as a result of a range of causes. We rank the causes according to their relative contributions. To quantify the occurrence of flood incidents for individual causes we use data from municipal call centres complemented with rainfall data and hydrodynamic model simulations. Results show that component failures and human errors contribute more to flood probability than sewer overloading by heavy rainfall. This applies not only to flooding in public areas but also to flooding in buildings. Fault tree analysis has proved useful in identifying relative contributions of failure mechanisms and providing quantitative data for risk management.     

城市防洪排洪规划重要因素探讨

对城市防洪排洪规划而言,"内河"与"外江"应赋予其不同的意义,文章对其进行新的界定。城市防洪排洪规划要确定防洪标准,本文通过分析论述,提出针对一个城市各条河流、溪流其设计防洪标准应分别确定,主要从汇水面积、其保护对象重要程度和人口多少等方面考虑确定。本文还针对福建城市地形特点,分析强调了采用高地自排对降低城市排洪压力,提高城市安全度的重要意义。     

ECONOMIC DESIGN OF FLOOD-ATTENUATION RESERVOIRS FOR URBAN AREAS EXPLOITING CATCHMENT HYDRODYNAMICS IN SOUTH-WEST UK

Runoff from new development in urban areas tends to increase the downstream flood peak which has to be attenuated or accommodated in the river channel to avoid increases in flood risk. The built environment close to the river often makes river-improvement works difficult, if not impossible. This paper introduces the concept of rising-limb attenuation, to mitigate downstream flood risk — especially in urban areas. Relying on the implicit difference in runoff times of concentration between rural and urban areas, it is possible to design efficient, self-regulating storage structures, to counteract increases in peak flow in the main urban watercourse, by attenuating the later contribution from less urbanised or rural tributaries. Because rising-limb attenuation is partial and temporary, volumes of storage are much less than for conventional attenuation reservoirs, with consequent savings in land take and costs. Because the controlled flow is also less, the associated structure is also generally smaller and simpler. Implementations of this type of structure have been carried out in two locations in the UK, and the outline design of these structures is described by reference to a case study.     

增强现实技术于洪水风险沟通中的应用

气候变迁,特别是洪水问题给地处三角洲的城市带来了与日俱增的风险。作为应对手段,提出一种整合性的洪水风险管理方法,该方法确保了洪水风险沟通在洪水风险管理战略中的重要地位。洪水的可视化作为洪水风险沟通的一种工具,在改变人们对洪水风险的观念方面有着强大的作用。它可以通过互动的方式,使当地的利益相关者了解洪水的剩余风险和未来风险。其中增强现实技术作为一种可视化手段,它的快速发展与应用为风景园林设计、规划与教育等领域提供了崭新的交互方式。首先,探讨增强现实技术(AR)在洪水风险沟通中的应用现状,并重点关注增强现实技术的2个关键应用领域:对现场决策的支持和针对高层次设计的可视化与对景观干预的评估。随后,展示一种基于增强现实技术所开发的应用,该款创新性的应用为洪水风险沟通提供了一种轻量化的可视化手段。     

Urban flood disaster management

Disaster management for urban areas is a growing priority owing to factors such as the relentless migration to cities, unplanned development, changing climate, and increasing operational and maintenance costs. New information and communication technologies offer improved opportunities to address these factors. This paper presents and describes the digital city concept as a means of capturing, analysing and applying (digital) information about the city area, its services, and their design and operation. In particular, the functionality of the digital city can be adapted for managing urban flood disasters. The paper highlights the need to manage the urban stormwater cycle integrated with urban planning. Urban flooding should be mitigated by having a judicious mix of both structural and nonstructural strategies, which are selected with the full participation of all stakeholders. The management of urban flooding is illustrated with application to the tropical island of St Maarten.     

Bayesian modeling of flood control networks for failure cascade characterization and vulnerability assessment

This paper presents a Bayesian network model to assess the vulnerability of the flood control infrastructure and to simulate failure cascade based on the topological structure of flood control networks along with hydrological information gathered from sensors. Two measures are proposed to characterize the flood control network vulnerability and failure cascade: (a) node failure probability (NFP), which determines the failure likelihood of each network component under each scenario of rainfall event, and (b) failure cascade susceptibility, which captures the susceptibility of a network component to failure due to failure of other links. The proposed model was tested in both single watershed and multiple watershed scenarios in Harris County, Texas using historical data from three different flooding events, including Hurricane Harvey in 2017. The proposed model was able to identify the most vulnerable flood control network segments prone to flooding in the face of extreme rainfall. The framework and results furnish a new tool and insights to help decision‐makers to prioritize infrastructure enhancement investments and actions. The proposed Bayesian network modeling framework also enables simulation of failure cascades in flood control infrastructures, and thus could be used for scenario planning as well as near‐real‐time inundation forecasting to inform emergency response planning and operation, and hence improve the flood resilience of urban areas.     

Decentralization-based optimization of detention reservoir systems for flood reduction in urban drainage areas

The paper introduces a decentralized approach to optimizing the flood reduction efficiency of multiple detention reservoirs in urban areas. The flood reduction effects of a detention reservoir system were regionally assessed, and a new model was then created using an optimization technique which involved coupling extraordinary particle swarm optimization with a flood simulation engine, Storm Water Management Model, EPA-SWMM, to identify optimal outlet designs for a detention reservoir system. When applied to the To Lich drainage network (Hanoi, Vietnam) the proposed method outperformed the present design, reducing flooding under the design flood event. The performance of the approach was verified by comparing it with the overall objective function of total flooded volume for different design floods. The better performance of the decentralized optimization approach described here, in terms of local and regional flood management, illustrated its effectiveness for urban flooding reduction.     

A Comparison of ERS-1 Satellite Radar and Aerial Photography for River Flood Mapping

The extent of floodwater inundation, whether caused by river flooding or coastal storm surges, is required quickly (a) to enable the planning of emergency relief and repairs to communications and services, and (b) for the production of river flood risk maps. Unfortunately, by their nature, most floods occur in bad weather, which can severely restrict the use of aircraft, and extensive cloud cover precludes the use of most earth observing satellites which rely on sensors operating at optical wavelengths.
Synthetic aperture radar, which can penetrate clouds, allows affected areas to be imaged, regardless of cloud cover or light conditions. This paper compares satellite acquired data of river flooding with photographic records obtained from a light aircraft to demonstrate the accuracy of the technique.     

Predicting floods from urban development scenarios: case study of the Dilúvio Basin,Porto Alegre,Brazil

It is well known that urbanization increases the hydrograph peak and overland flow volume from drainage basins, and that the concentration time of flood flows is diminished. To predict the effects of future urban development on the flood regime, the design hydrograph must be estimated. Nevertheless, the information from which to estimate a design hydrograph is limited where planning procedures (such as the `Urban Master Plan' of some Brazilian cities) specify only the type of urban land use (residential, industrial, etc.) and the recommended population density in areas where development is planned. This paper presents the relationship between parameters of a hydrologic model and urban development characteristics as set out in the Urban Master Plan. A hydrologic model IPH IV [C. E. M. Tucci, B. Braga, A. L. L. Silveira, RBE Caderno de Recursos Hı́dricos 7 (1) (1989)] was used together with a GIS to predict the hydrograph corresponding to alternative urbanization scenarios. Model parameters were fitted and verified using recorded data from the Dilúvio Creek in Porto Alegre, Brazil. The model was applied to predict the design hydrograph for different risks in accordance with the city's Urban Master Plan. Flooded areas corresponding to a storm rainfall with return period 25 years were calculated by simulation, the flooding being mainly due to flow obstruction by bridges.     

RCP8.5情景下流域景观水文与泥沙 动态连通变化研究

在气候变化背景下,水文连通是风景园林学学科中 景观水文研究的热点和重点之一。目前的景观水文连通研究 多基于静态地表,而忽略地表演化过程,尤其是河底泥沙动态 变化。在总结现有水文连通研究的基础上,结合气候预测模 型、水动力地表景观演变模型及景观连通指数研究方法,以英 国赛文河凯尔苏斯流域为研究区,采用UKCP18气候模型预 测RCP8.5情景下未来10年间(2021—2030年)日降雨量, 运用凯撒二维水动力地表景观演变模型(CAESAR-Lisflood) 模拟10年连续河流演化及淹没模式变化,基于景观连通指数 评价流域景观水文的动态连通变化。结果表明：泥沙变化对淹 没模式和水文连通性产生影响,未来10年间整体连接度(IIC)与 可能连通性(PC)变低,雨季水文IIC与PC变化幅度较大,旱季 平稳。凯尔苏斯流域洪泛区域比河道的沉积作用更明显,流域 总沉积量是侵蚀量的4.6倍。泥沙输移作用使得淹没面积减少 0.25km2 、流域总水量减少40%,水文IIC与PC降低     

高密度沿海地区洪涝风险评价与适应性规划策略 ——以深圳湾地区为例

气候变化背景下，高密度沿海城市受 到风暴潮和极端降雨引起的洪涝灾害冲击。文 章基于韧性理论构建城市空间洪涝风险指标 体系，制定该评价框架的实施路径；基于水文 软件Mike21、GIS平台及其空间网络分析插件 sDNA，复合“天鸽”台风风暴潮与极端降雨情 景，整合深圳湾地区的路网和土地利用进行危 险性、暴露度、脆弱性和适应能力等多源数据； 通过GIS栅格计算得到各要素层分析及洪涝风 险评价可视化地图，结果显示，潮、洪、涝突破 刚性标准加剧了危险性，高密度城市环境增大了 危险区域的暴露度，路网和土地利用布局具有 一定脆弱性，需完善应急疏散和避难场所规划以增强适应能力；根据评价地图识别高风险片区，从路网和土地利用等城市空间物质要素出发， 提出应对洪涝灾害的适应性规划策略。     

The White Cart Water Flood Alleviation Study using Hydrodynamic Mathematical-Modelling Techniques

This paper describes a hydrodynamic mathematical-modelling study to investigate the flooding problem and to recommend various flood-alleviation measures for the White Cart Water on the southern side of Glasgow. The mathematical model covers 36 km of the White Cart to the tidal reaches at the confluence with the River Clyde, and includes 7 km of one of the major tributaries where regular flooding is also a problem. A key aspect of the study was the close proximity of the modelling team which permitted a close scrutiny of the river during high-flow events. From these observations the team obtained a thorough appreciation of river behaviour during potential flood situations, which provided a reliable and comprehensive set of data for model calibration over a wide range of conditions. The proposals for flood alleviation have far-reaching implications and require major capital expenditure. At present they are being examined by Strathclyde Regional Council in consultation with the many interested parties.     

Modelling sewer discharge via displacement of manhole covers during flood events using 1D/2D SIPSON/P-DWave dual drainage simulations

In urban areas, overloaded sewers may result in surcharge that causes surface flooding. The overflow from sewer systems mainly starts at the inlets until the pressure head in the manhole is high enough to lift up its cover, at which stage the surcharged flow may be discharged via the gap between the bottom of the manhole cover and the ground surface. In this paper, we propose a new approach to simulate such a dynamic between the sewer and the surface flow in coupled surface and sewer flow modelling. Two case studies are employed to demonstrate the differences between the new linking model and the traditional model that simplifies the process. The results show that the new approach is capable of describing the physical phenomena when manhole covers restrict the drainage flow from the surface to the sewer network and reduce the surcharge flow and vice versa.     

Flood-Plain Mapping of the River Leam and River Itchen

As part of the requirements of s. 105 of the Water Resources Act 1991, the Environment Agency is producing flood-plain maps of all major rivers. Where no historic data are available for a large flood event, mathematical models are used to simulate 100-year design flood flow events, which allows the definition of flood-prone areas. These maps, together with a database of the water levels and flows, will form part of a national Flood Plain Information System.
This paper describes the development and generation of flood-plain maps for the Rivers Leam and Itchen in Warwickshire. The data collection and review of topographic and hydrometric data are outlined. Procedures for combining information from gauged data, historical flood data and methods based on catchment characteristics form the basis for estimating design input flows to hydraulic models. Modelling principles and data requirements of two different hydraulic models, used to estimate peak water levels of design return period, are described.