Flood Warning, Forecasting and Emergency Response

verfasst von: Kevin Sene

Verlag: Springer Berlin Heidelberg

Enthalten in: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik" , Springer Professional "Wirtschaft"

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Über dieses Buch

Recent flood events in Europe, the USA and elsewhere have shown the devastating impact that flooding can have on people and property. Flood warning and forecasting systems provide a well-established way to help to reduce the effects of flooding by allowing people to be evacuated from areas at risk, and for measures to be taken to reduce damage to property. With sufficient warning, temporary defences (sandbags, flood gates etc) can also be installed, and river control structures operated to mitigate the effects of flooding.

Many countries and local authorities now operate some form of flood warning system, and the underlying technology requires knowledge across a range of technical areas, including rainfall and tidal detection systems, river and coastal flood forecasting models, flood warning dissemination systems, and emergency response procedures.

This book provides a comprehensive account of the flood forecasting, warning and emergency response process, including techniques for predicting the development of flood events, and for issuing appropriate warnings. Related topics, such as telemetry and information systems, and flood warning economics, are also discussed. For perhaps the first time, this book brings together in a single volume the many strands of this interesting multidisciplinary topic, and will serve as a reference for researchers, policy makers and engineers. The material on meteorological, hydrological and coastal modelling and monitoring may also be of interest to a wider audience.

Inhaltsverzeichnis

Frontmatter

Flood Warning

1. Introduction

Recent flood events have shown the devastating impact that flooding can have on people and property. Flood warning and forecasting systems can help to reduce the effects of flooding by allowing people to be evacuated from areas at risk, and to move vehicles and personal possessions to safety. With sufficient warning, temporary defences can also be installed, and river and tidal control structures operated to mitigate the effects of flooding. Many countries and local authorities now operate some form of flood warning system, and the underlying technology requires knowledge across a range of technical areas, including rainfall and tidal detection systems, river and coastal flood forecasting models, flood warning dissemination systems, and emergency response procedures. This introductory chapter provides a general overview of the flood warning process, approaches to flood forecasting and emergency response, and the nature of flood risk.

2. Detection

Most flood warning systems use near real time measurements of meteorological and river or coastal conditions to guide operational decision making. Depending on the application, this may include information on rainfall, wind speeds, sea state, tidal levels, river levels and other parameters, such as snow cover. Remote sensing techniques such as weather radar and satellite may also be used, together with the outputs from Numerical Weather Prediction models and nowcasting techniques. This chapter provides a general introduction to these and other techniques for monitoring meteorological, river and coastal conditions for flood warning applications. Telemetry systems are also discussed, together with approaches to designing telemetry networks for flood warning applications.

3. Thresholds

Flood warning thresholds define the meteorological, river and coastal conditions at which decisions are taken to issue flood warnings, whilst flooding thresholds are the values at which flooding occurs. Normally, a flood warning threshold will be set to achieve an acceptable lead time before the flooding threshold is reached, or may be time based (as with tropical cyclones, for example). Alternative names for flood warning thresholds include triggers, criteria, warning levels, critical conditions, alert levels and alarms, and sometimes a range of values will be required as warnings are escalated from advisories (or watches, or pre-warnings) through to full warnings. Threshold values may be set based upon experience or analysis of historical data, or using conceptual, data based or process based modelling studies. Values may be fixed (static) for all flood events, or dynamic, varying depending on how each event unfolds. This chapter describes a range of techniques ranging from simple fixed flood warning thresholds through to probabilistic approaches, together with several examples of approaches to performance monitoring of thresholds.

4. Dissemination

Although organisational structures can differ widely between countries, a regional or national flood warning service typically has a wide range of responsibilities, which can include monitoring meteorological, river and coastal conditions, development and operation of flood forecasting models, and dissemination of flood warnings to the emergency services, local authorities and the public. Other responsibilities may include operation of control structures to mitigate flooding impacts, assisting with or coordinating the emergency response (evacuation, sandbags etc.), and contributing to post event assessments. These various activities may be performed within an overall framework of flood warning targets and performance monitoring, so that the lessons learned from each flood event guide future investments and technological improvements. This chapter discusses some of these organisational and procedural aspects to providing a flood warning service, and gives an overview of techniques for disseminating flood warnings and for implementing a flood warning system. Later chapters describe how the flood warning service fits into the wider emergency response to a flood event, which can potentially involve participants from many different organisations.

Flood Forecasting

5. General Principles

Flood forecasting models are an important component in many flood warning and emergency response systems. Models can assist by providing advance warning of the likely timing and magnitude of flooding, and in helping to understand the complexities of a flood event as it develops. Models outputs may also be used in decision support systems for flood event management and the operation of flow control structures. The techniques used for flood forecasting have many similarities to the methods used for simulation modelling of river and coastal processes. However, the design may be constrained by the availability of real time data, and computer systems on which to operate the model, although there is the advantage that model outputs can be updated to help to account for differences with observed values; a process which is often called data assimilation. Ensemble and probabilistic techniques are also increasingly being developed to provide information on model uncertainty to users of model outputs, and to allow a more risk-based approach to decision making. This chapter provides a general introduction to these issues and to the topic of flood forecasting model calibration and performance monitoring.

6. Rivers

Flood forecasting models for rivers can range from simple empirical relationships to complex integrated catchment models. Forecasts may be based simply on river level or flow observations at locations upstream of the site of interest, or use observations and possibly forecasts of rainfall to gain additional lead time. This chapter begins with a discussion of the main factors which can influence the design of a river flood forecasting model, including the forecasting requirement and the availability of real time data, and then describes two main categories of model; rainfall runoff models, and river channel (flow routing) models. Examples are provided for a range of process-based and conceptual modelling techniques, and for data-based approaches such as transfer function and artificial neural network models.

7. Coasts

Coastal flood forecasting models are used to estimate conditions at or near locations which may be at risk from flooding, such as towns, ports and harbours, and coastal roads and railways. Forecasts may also be required at structures, such as tidal barriers, to assist with operations to reduce the risk of flooding. Models can range from simple empirical relationships to complex process-based models combining offshore, nearshore, wave overtopping and flood inundation components. Forecasts may be based primarily on coastal observations, or also make use of the surge, wind and wave forecasting outputs provided by national meteorological services and coastal observatories. This chapter describes some of the issues in selecting an appropriate modelling approach and then discusses a range of process based and data based techniques for coastal flood forecasting.

8. Selected Applications

Previous chapters have described the main techniques which are used in river and coastal flood forecasting, whilst this chapter presents a selection of forecasting applications. These include integrated catchment forecasting models, and forecasting techniques for flash floods, snowmelt, ice jams, dams and reservoirs, control structures, urban drainage flooding, and geotechnical risks, such as Tsunami, debris flows, and dam break. The chapter also includes several examples in fields which are closely related to flood forecasting, such as the real time control and optimisation of reservoir and urban drainage systems. Some themes which run throughout the chapter are the use of ensemble and probabilistic techniques to provide information on risk and uncertainty, and the use of process-based, conceptual and data-based modelling approaches.

Emergency Response

9. Preparedness

As with other types of natural hazard, the effectiveness of response to a flood event can be improved if an emergency plan has already been prepared, so that all participants understand their roles and responsibilities, including the overall chain of command. The potential disruption from flooding also needs to be considered, including the possibility of communication, instrumentation, computer and other systems failing, and access and evacuation routes being cut by flood water. Risk assessment techniques are also increasingly used to assess the resilience of response procedures, together with developments in information technology for the spatial analysis and visualisation of flood extent relative to properties, infrastructure and transport routes. This chapter provides an introduction to these issues, and discusses the general trend towards multi-hazard systems, which share systems and resources across many types of threat.

10. Response

Flood warnings provide local authorities, the emergency services, the public and others with time to take actions to reduce the risk from flooding, and information on the likely extent and locations of flooding. Actions which can be taken before a flood starts include installation of temporary defences, operation of flow control structures, protection of personal property, evacuation of people from areas at risk, and positioning of emergency vehicles and other assets in locations which may become inaccessible due to flood waters. Increasingly, decision support systems are also being developed to assist in responding to flood events, and can provide advice on strategies for evacuating property, casualty management, and emergency repairs to flood defences. This chapter considers these issues, together with the more general topic of dealing with uncertainty in decision making during flood events.

11. Review

Reviews of flood warning systems are often required following major flood events, and may form part of a programme of continuous improvement, sometimes linked to performance targets for different aspects of the system. Performance monitoring should ideally cover all aspects of the system, including detection, forecasting, dissemination, and response to warnings, together with feedback from users on satisfaction with the system. The lessons learned from post event assessments, and recommendations from regular reviews, can then guide future investments, and provide baseline information for use in economic assessment and prioritisation exercises. However, improvements need not necessarily require significant investment, and much can be gained from improving operating procedures, and closer collaboration between the various participants in the flood warning process, including communities and their representatives. This chapter discusses these various issues, and highlights some common themes from earlier chapters on ways of improving flood warning, forecasting and emergency response systems.

Backmatter

Titel: Flood Warning, Forecasting and Emergency Response
verfasst von: Kevin Sene
Verlag: Springer Berlin Heidelberg
Electronic ISBN: 978-3-540-77853-0
Print ISBN: 978-3-540-77852-3
DOI: https://doi.org/10.1007/978-3-540-77853-0