From flood control to flood adaptation: a case study on the Lower Green River Valley and the City of Kent in King County, Washington

Despite massive investment in flood control infrastructure (FCI), neither cities nor rivers have been well served-flooding continues to challenge cities around the world, while riverine ecosystems are degraded by FCI. Although new flood hazard management concepts have shifted the focus away from FCI, many cities continue to count on FCI to prevent flood damage. It is assumed that existing built-up areas can only count on FCI, as large-scale retreat is often impossible. However, flood adaptation-retrofitting the built environment to prevent damage during flooding-as an option is often ignored. This paper argues against the continual use of FCI to prevent flood damage by reviewing FCI's established problems. The paper examines human-river interactions associated with FCI, focusing on the feedback mechanisms in the interactions, with a case study on the Lower Green River (LGR) valley in King County, Washington, USA. An urban ecology research model is employed to organize the case study, where interactions between floodplain urbanization, FCI, flow and sediment changes, flood risk, and riverine ecosystem are explored and two feedback mechanisms-river adjustment and flood risk perception-are explicitly addressed. The resulting complex dynamics, in terms of cross-scale interactions, emergence, nonlinearity, and surprises, are synthesized and limitations of FCI outlined. Flood adaptation is explored as a plausible alternative to flood control to nurture flood resilience. A management scenario of flood adaptation for the City of Kent-the largest municipality in the LGR valley-is developed to discuss the implications of flood adaptation on flood risk and river restoration.