Managing Flood Risk

Innovative Approaches from Big Floodplain Rivers and Urban Streams

Anna Serra-Llobet, G. Mathias Kondolf, Kathleen Schaefer, Scott Nicholson, Anna Serra-Llobet, G. Mathias Kondolf, Kathleen Schaefer, Scott Nicholson, Anna Serra-Llobet, G. Mathias Kondolf, Kathleen Schaefer, Scott Nicholson

• Publisher: Palgrave Macmillan
• Year: 2018
• ISBN:
  9783319716732
• Topic: Physical Sciences
• Subtopic: Geography
• Index: Geography

The past half century has seen an evolution in thinking from 'flood control' to 'flood risk management', recognizing that risk results from both hazard and vulnerability. Rather than rely only on engineering structures to reduce flood magnitude or extent, recent policies emphasize avoiding construction in flood-prone areas (or moving people from floodplains), reducing impacts on exposed populations through early warning systems, and insurance to aid in recovery. Implementing this new approach faces many challenges but also offers opportunities for synergies, as described in this book for a range of large floodplain rivers and smaller urban streams across North America and Europe. This book is unique in presenting the voices of those on the front lines of implementing a new paradigm in flood risk management, each river with a unique set of challenges and opportunities derived from its specific geography as well as differences in governance between the American and European contexts.

© The Author(s) 2018

Anna Serra-Llobet, G. Mathias Kondolf, Kathleen Schaefer and Scott Nicholson (eds.)Managing Flood Riskhttps://doi.org/10.1007/978-3-319-71673-2_1

Begin Abstract

1. Introduction

Anna Serra-Llobet^{1, 2} , G. Mathias Kondolf^{1, 3} , Kathleen Schaefer^{1, 4} and Scott Nicholson^{1, 5}

(1)

University of California Berkeley, Berkeley, CA, USA

(2)

Aix-Marseille University, Marseille, France

(3)

University of Lyon, Lyon, France

(4)

Federal Emergency Management Agency, Oakland, CA, USA

(5)

US Army Corps of Engineers, Washington, DC, USA

Anna Serra-Llobet (Corresponding author)

G. Mathias Kondolf

Abstract

Managing flood risk instead of ‘controlling floods’ is a key change in approach for managing floods and floodplains. In the context of floods, hazard refers to the magnitude or height of a given flood and its probability of occurring. Vulnerability refers to the social assets exposed to damage from flooding. Risk combines both hazard and vulnerability. Thus managing flood risk implies making interventions at all points of the flood risk cycle, including not only structural measures to reduce flood magnitude or frequency (reducing hazard) but also land-use planning (to reduce assets exposed), early warning systems, insurance, and acting within the context of multiple objectives. Recent experiences in implementing flood risk management along large floodplain rivers and smaller urban streams in America and Europe manifest a wide range of environmental and institutional settings, and thus opportunities and constraints unique to each setting.

Keywords

Flood risk managementFlood controlLarge floodplain riversUrban rivers

End Abstract

Human societies have long settled along rivers and for just as long have been dealing with flooding. Today flooding remains by far the biggest and costliest natural hazard globally. Early societies accommodated annual and less frequent cycles of flooding through locating settlements and infrastructure on higher ground where possible, raising structures, and seasonal occupation of lowlands. Diverting floodwaters away from cities through bypass routes or out-of-basin diversion was practiced by the ancient Nabateans (Mays 2010) and by the Romans, who debated the relative impacts of diverting flood flows of the Tiber into neighboring basins (Keenan-Jones 2013). As technologies evolved, larger-scale structural methods of control were employed, leading to the massive dams built from the mid-twentieth century onward, some of which have included flood control among their objectives and extensive systems of dikes to limit flooding.

The past half century has seen an evolution in thinking from flood control to flood risk management , reflecting increased understanding that building structures to control floods is only one of many possible approaches available to societies (Sayers et al. 2013). Understanding floods as a process, and not as isolated events in time and space, we can distinguish four phases for flood risk management in the framework of the flood risk management cycle : (1) the characterization of hazard and risk (assessment and mapping); (2) mitigation strategies, which include prevention measures (e.g., land-use management) and protection measures (e.g., levees and dams); (3) emergency management, meaning preparation and response; and (4) recovery at short and long terms (Serra-Llobet et al. 2016) (Fig. 1.1).

Fig. 1.1

The flood risk management cycle (Source: Image adapted from Serra-Llobet et al. 2016)

Before going much further, it may be worthwhile to define ‘risk’ and distinguish the terms from related terms such as hazard, exposure, and vulnerability. As noted by prior authors (e.g., Merz et al. 2010; Gallopin 2006), these terms have been variously used and defined. Here we use hazard for the physical process and its likelihood of occurring, for example, a flood reaching a given elevation with a given probability each year. Vulnerability denotes the societal assets exposed to flooding and accounts for the socio-economic system to recover from a flood. Risk results from both the hazard and vulnerability. If there are no people, infrastructure or other assets that we value on the floodplain to be damaged, there is no risk, no matter how big the floods are (i.e., no matter how high the hazard).

By siting villages on high ground above the floodplain, as was the case along the Upper Rhine Valley (Plate 2002), traditional societies reduced their vulnerability but lacked any means to reduce the frequency or magnitude of flooding (the hazard). However, in the twentieth-century ‘flood control’ approach , structural measures were implemented to reduce the hazard (i.e., magnitude and frequency of flooding). These structural measures (e.g., dams to reduce the flood flow in the river, levees to keep floodwaters out of a part of the natural floodplain) commonly induced further settlement in floodplains that were still exposed to flooding (though less frequently), thereby increasing vulnerability (Tobin 1995).

Moreover, the conventional structural measures were typically single-purpose engineering structures, with negative environmental consequences. In the developed world, increased requirements for environmental protection and restoration, along with recognition of global change and its effects on water supply, have motivated adoption of integrated flood risk management (IFRM) , in which measures to manage floods must be developed and analyzed in a broader and “integrated” context, and multi-objective projects (with environmental, water quality, and recreational benefits) are preferred over single-objective projects. While there is increasing agreement that IFRM is a good idea, putting it into practice remains a challenge. Diverse views have been advanced regarding which governance systems are better suited to implementing IFRM (e.g., bottom-up approaches as in the USA or top-down as in the EU) (Serra-Llobet et al. 2016). Floods have a geographical extent, but managing them is done in the context of administrative, social, and cultural boundaries, which commonly do not align. The regulatory and political frameworks of a region determine to some extent what options are feasible.

IFRM also implies moving from a site- or project-based approach to a catchment-scale systems approach , which means not only relying on structural measures but also incorporating non-structural measures such as land-use planning, flood mapping, early warning, and controlled flooding for ecological benefits.

The options available to manage flood risk can be seen in a framework of temporal and spatial scales, as illustrated in Fig. 1.2. For example, actions to reduce the vulnerability of socio-economic assets (such as land-use planning to keep buildings out of floodplains) require longer time horizons to affect settlement patterns and decisions on siting large infrastructure.

Fig. 1.2

Different spatial scales for flood risk management (a) Examples of human effects on flood risk and flood risk management measures at different temporal and spatial scales (b) (Source: (b) table adapted from Merz et al. 2010)

Increasingly, we see public agencies and other actors attempting to implement IFRM in the face of multiple challenges. These challenges vary with context and can be quite different along major river floodplains (where the flood hazard results from waters conveyed from upper parts of the basin, overflowing onto the floodplain) and urban areas (where most flood hazards result from local rainfall that does not drain away as fast as it falls). Moreover, the context of land-use constraints, prior hydrologic modifications, and governance varies among sites, creating unique situations for which innovative approaches are needed.

While the concept of IFRM and some of its implementation dilemmas have been discussed in the literature, this book is unique in its collection of experiences in the voices of those on the ‘front lines’ of implementing integrated approaches in the context of multiple constraints, the greatest of which are usually inst...

Table of contents

• Cover
• Front Matter
• 1. Introduction
• Part I. Big River Basins
• Part II. Urban Streams
• Back Matter