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<br />ROGER A. PIELKE. JR.
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<br />2.3. LEVEES 'PREVENT' DAMAGES
<br />
<br />The United States, one flood expert has commented. has had an 'undyin.g love af-
<br />Fair' with levees (Tobin, 1995). Another flood expert has called the late-eighteenth!
<br />early nineteenth century policy of sole reliance on levees to control floods 'perni-
<br />cious beyond belief' (Wright. 1996, p. 247). A levee is a structure buil~ to keep w~-
<br />tef from inundating an area that would otherwise be flooded,. The Umted Slales IS
<br />home to approximately 25.000 miles of levees - or enough to encircle the world at
<br />the equator (FlFMTF, 1992). The U.S. Army Corps of Enginee~s has been respon.
<br />sible for building more than 10,500 miles of levees. Levees bU,11t by other fed~raJ
<br />and state agencies, as well as by individuals, make up the remamder. T~e fundmg,
<br />design, construction, and repair of levees by the federal government IS overs~en
<br />by five federal agencies: USACE, Agrkulture, National Resources. C?nservatIon
<br />Service,t Federal Emergency Management Agency (FEMA), Economic Devel.op~
<br />ment Administration, and HUD (Housing and Urban Development). The mU~llple
<br />agencies and their differing requirements and responsibilities 'confuses' the Issue
<br />of levee systems (Tobin, 1995, p. 364). Local agencies and privately~owned levees
<br />further complicate the issue.
<br />According [0 Tobin (1995, p. 365) levees can serve to actual1~ increase the
<br />potential for flood losses. He calls this the 'levee effect' and defines It as follows:
<br />
<br />Once [a levee] has been constructed, however, the structure may'?enerate a
<br />false sense of security to the extent that floodplain inhabitants perceive that all
<br />flooding has been eliminated. With the incentive to take precautions removed,
<br />few residents will be prepared for remedial action in the event of future floods.
<br />Even more costly, however, this false sense of security can also lead to greater
<br />development in the so~called safe areas, thus adding to the property placed
<br />at risk. .. when the levee does fail, the increase in development can ac~ually
<br />raise losses even higher than if no levee system had been constructed IR the
<br />
<br />firsl place,
<br />The 'levee effect' can increase society's vulnerability to floods in two ways: by
<br />creating a sense of complacency, which can act to reduce p~eparedn~ss and by
<br />crearing incentives to build structures in areas subject to floodlOg. Tobm observes
<br />that a comprehensi\le study of the 'levee effect' has. yet to be undertaken. .
<br />The fallacy that 'levees prevent damages' is a subset of a much broader Issue
<br />about the role of structural measures in flood mitigation. Structur~1 appro~ches to
<br />!load control are characterized by attempts to keep high water from lOun~at~ng p~b-
<br />lie and private prope~ty and thus causing damage. Since the 1940s, be~lOmng. With
<br />\he pioneering work of Gilbert White, f1oodpl~in m~na~ement has IOcre~SIO~IY
<br />included 'nonstructural' approaches that emphaSize adJustmg human behaVior (see
<br />
<br />. Boln levees and floodwalls are defined as a form of 'dike' - a general term for 'longitudinal
<br />.~lrUC1Ure.~ Ihat serve 10 retain water' (FIFMTF. 1992. p. 12-27). This paper uses the more common
<br />lerm 'levee' 10 refer 10 alllypes of levees, f1oodwall.~. and dikes.
<br />t Formerly the Soil Conservation Service.
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<br />NINE FALLACIES OF FLOODS
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<br />42/
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<br />FIFMTF (J 992), Chapters 12 and 15 for discussion). Issues of structural and com-
<br />plementing nonstructural approaches 1O flood mitigation go well beyond the scope
<br />of this paper. It is worth noting, however, that in spite of widespread agreement
<br />among flood experts that structural measures alone cannot adequately address the
<br />nation's flood problem, the proper role of structural measures has yet to be ade~
<br />quately defined. Lack of understanding of the 'levee effect' is a prime example
<br />of how an incomplete understanding of the role of structural and nonstructural
<br />measures in flood mitigation limits what can be authoritatively said with respect to
<br />the flood problem.
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<br />2.4. FLOOD FORECASTS ARE UNIVERSALLY AVAILABLE
<br />
<br />The Unified National Program for Floodplain Management report asserted that
<br />'regional warnings for floods and hurricanes are becoming universally available'
<br />(FIFMTF. 1994, p, 16), This slands in stark contrast to Changnon (1996. p, 309)
<br />who stated with respect to the 1993 Midwest flood that 'the flood condition pro-
<br />nouncements of the National Weather Service (NWS) and those of the Corps of
<br />Engineers for the Sl. Louis arca were of\en inaccurate and sometimes controver~
<br />sial' (cf. Gruntfest and Pollack, 1994). As a consequence, 'these forecasts and
<br />pronouncements likely worked to the detriment of the strategies used to fight the
<br />flood, shipping alternatives, and other flood-impacted endeavors' (p. 27). Further-
<br />more, even the Weather Service's self evaluation found 'substantial opportunities
<br />for improvements' (DOC, 1994, p. 2~ 1). More recently, residents of the Red River
<br />of the North basin have criticized the flood forecasts issued during the spring 1997
<br />floods (see, for example, Glassheim, 1997). In short, in spite of the progress made
<br />over the last century in weather and flood forecasting, there remains considerable
<br />potential for improvements in flood forecasts. Further, there also remains a vast
<br />potential for improved U$e of those forecasts by decision makers (Pie!ke, 1999;
<br />Changnon, 1996: cf. Grunlfesl and Pollack, 1994),
<br />One potential area for improveme[Jt of flood forecasting lies with continuing
<br />improvements in 'Quantitative Precipitation Forecasting' (QPF), which is defined
<br />as 'the forecasting of the amount of rain or water equivalent of frozen precipitation
<br />that will fall over a particular area over a given period' (Schwein, 1996, 'p. I). Such
<br />improvements have been described as 'steady, albeit slow' (Krzysztofowicz, 1995,
<br />p. 1143). The goal of using QPF in the flood forecasting process is to provide a
<br />longer lead time for flash flood and river stage forecasts. Of course, the success of
<br />this tool depends on large part upon the ability to forecast reliably the amounl of
<br />precipitation that will fall over a particular watershed. To date, QPF has not been
<br />fully implemented. Results have been mixed in experimental uses of QPF with
<br />both improvements and degradation in forecasts. One review cites several studies
<br />of the use of QPF tha.t show benefits to decislons a.ssocia.ted with 600d warning.
<br />reservoir control, and commercial navigation (Krzysztofowicz, 1995). According
<br />to Schwein (1996) a key to beneficial use of QPF in flood forecasting will be to train
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