E D I T O R I A L

How safe is safe enough?

DOI: 10.1111/j.1753-318X.2011.01124.x

It is more or less axiomatic in the Journal of Flood RiskManagement that flood management decisions should bebased upon risk. Flood risk management decisions involvethe identification of a range of possible flood risk manage-ment measures (structural and non-structural) and evaluat-ing their potential benefits, in terms of risk reduction, nowand in the future. Then comes the difficult decision: by howmuch should risk be reduced? Broadly there are two poten-tial approaches to addressing this problem: cost-effectivenessanalysis and cost–benefit analysis. Both are fraught withdifficulties.

Cost-effectiveness analysis seeks to identify the least-costoption that satisfies some performance requirement. Inflood risk management, the primary performance require-ment will be in terms of acceptable risk, although there willoften be other constraints in terms of environmental stand-ards and socio-political acceptability of the proposed meas-ures. Definition of acceptable risk is a thorny issue. Differentcountries have very different approaches, and indeed cul-tural reactions, to the very notion of acceptable risk. In theNetherlands analysis of societal risks in terms of F-N curvesis well established. Standards of dike reliability are estab-lished for all dike rings, ranging from 1:10 000 years on thecoast to 1:1250 years on the Rhine river channels. The UnitedKingdom explored ideas of acceptable societal risk, notablyduring the notoriously long-winded public enquiry for theSizewell B nuclear power station but then retreated fromfixed thresholds for acceptable risk to the more flexible ‘AsLow As Reasonably Practicable’ (ARARP) framework. Inpractice, that means that there is a range of risk thresholdsderived from government guidance, insurance availabilityand implicit social contract. Guidance for development inflood plains introduces thresholds at 1:100 years for riverflooding and 1:200 years for coastal flooding. Meanwhile,availability of domestic flood insurance provides anotherthreshold of public acceptability. In the United Kingdom thenow fragile ‘statement of principles on flood insurance’,which sets out the conditions in which insurance companieswill, for the time being at least, offer flood insurance domes-tic customers, implies an acceptable probability of floodingof about 1:75 years. A flood probability greater than this willnot be acceptable because flood insurance would be unavail-able to new customers, so they would not be able to obtain amortgage on their home. A similar relationship betweenflood probability and insurance availability exists in the

United States where levees have to be certified for Federalflood insurance to be made available.

A further criterion for acceptability relates to businessconfidence. In 2008 the Dutch Deltacommissie proposed anincrease in standards of flood protection by a factor of 10.Although flood defence standards were already the highest inthe world, in the aftermath of Hurricane Katrina and amidstnew scientific evidence about the possibilities of sea levelrise, this proposed increase in standard was a clear signal tothe world that the Netherlands would be in business comewhat may.

It is not hard to see how an emphasis on absolute thresh-olds may lead to perverse decisions. The cost of reducing theprobability of flooding from just over the threshold to justunder may be excessive; is it worth it? An acceptable prob-ability threshold does not necessarily account for the severityof the consequences of flooding, which, from a risk perspec-tive, we should be taking account of. Cost–benefit analysisprovides a more rational framework for the setting of riskstandards. Society should, and from time to time does, objectto disproportionate sums being spent on achieving highstandards of safety when those resources could be spentmore effectively at reducing another risk or indeed providingother benefits to society. Cost–benefit analysis provides arational framework for making these resource allocationchoices and has become the dominant approach to theappraisal of public investment schemes in many countriesworldwide. Yet cost–benefit assessment is fraught with well-known methodological problems, in particular in relation tothe proper valuation of loss of life and social and environ-mental impacts. Increasingly we aim to deliver flood riskmanagement schemes that yield other benefits, for examplewith respect to waterfront development or habitat restora-tion, but valuation of those benefits is challenging. Discount-ing means that costs and benefits that are incurred a longtime in the future can have a negligible effect on cost–benefitdecisions, even though we can foresee situations in whichfuture generations might regret decisions taken by presentgenerations, for example in relation to allowing develop-ment in vulnerable locations. Intergenerational issues areone version of the many equity issues that cost–benefitanalysis raises; who incurs risks and benefits, and who pays?It is particularly tricky to estimate the opportunity costs offoregone development in flood plains. In this Journal wewould argue that prudent flood-plain zoning policies are an

J Flood Risk Management 4 (2011) 271–272 © 2011 The AuthorsJournal of Flood Risk Management © 2011 The Chartered Institution of Water and Environmental Management

essential aspect of flood risk management. But we must notoverlook the fact that these policies limit developmentopportunities and so brings a cost to society. Yet it is almostimpossibly difficult to evaluate the wider societal benefits ofdevelopment that would have materialised had developmentbeen permitted.

In theory cost–benefit analysis would allow the identifi-cation of an ‘optimal’ level of risk, now and in the future. Inpractice the multiple perspectives on risks mean that it isarguable as to whether a unique optimum exists. The attend-ant uncertainties mean that it would be impossible to iden-tify it precisely even if it did exist. What cost–benefit analysiscan provide is evidence to inform resource allocation deci-sions and a mechanism to avoid the extremes of under- orover-adaptation. Cost–benefit analysis is open to distortion(for example when it is being used to justify the expenditureof other people’s money), but at least it provides a quantified

framework that can be opened up to scrutiny in whichassumptions, data and calculations are challenged.

We need to be realistic about what acceptable risk thresh-olds and cost–benefit analysis can and cannot provide. Ouremphasis is upon improving the process as well as the mate-rial outcomes of flood risk management decisions. Animportant principle in flood risk management is that thedepth of analysis should be in proportion to the severity ofthe risk and the magnitude of the mitigation decision. Notall flood risks will require a detailed analysis, but on thewhole we could do much better in evaluating risks, costs, andattendant uncertainties and in communicating them to deci-sion makers and other stakeholders. The Journal of FloodRisk Management seeks to contribute to this endeavour.

Jim HallAssociate Editor

272 Editorial

© 2011 The AuthorsJournal of Flood Risk Management © 2011 The Chartered Institution of Water and Environmental Management

J Flood Risk Management 4 (2011) 271–272