Floodplain regulation strives to balance the benefits of reducing flood hazards to human life and property against the costs of limiting encroachment on areas that, under normal conditions, have appeal for many kinds of development. The 1990 enactment of a zero-rise ordinance in King County tightened floodplain regulations enough that agencies responsible for maintaining safe bridges and roadways are now hampered by excessive design and construction costs. Agencies responsible for maintaining transportation safety must now work in a highly restrictive regulatory environment in which bridge replacements and improvements are prohibitively expensive or impossible without variances from one or more regulations.
The general purpose of this project was to evaluate the implications of the zero-rise regulation for bridge builders in the King County Roads Division and the Washington State Department of Transportation. The report
On the basis of this work, the following conclusions were drawn: 1) King County has more restrictive floodplain regulations than other locales in which a zero-rise water surface constraint has been adopted. The report recommends that conflicts between the zero-rise regulation and Surface Water Design Manual (SWDM) constraints be resolved on the basis of the relative importance of each for preventing flood damages. 2) The zero-rise ordinance has caused King County significant cost increases for bridge work, whereas the benefits of the ordinance have not been formally demonstrated. 3) The zero-risk paradigm has been found to be unworkable in well-tested examples of national environmental policy. 4) The intended balancing of flood mitigation against increased bridge expense has not occurred.