Cities are increasingly interested in the construction, restoration, or conservation of wetlands in urban areas in order to benefit from the ecosystem services they provide–in particular, stormwater management services. However, wetlands, once incorporated into urban landscapes and stormwater management systems, face the same land use change pressures as all other categories of urban land use, only with potential city-wide impacts to pluvial flood risk. Here, we examine several proposed scenarios for urban development in Valdivia, Chile, which already has a network of inland wetlands incorporated into its stormwater management system, in order to quantify their proposed changes on wetland and watershed extent and watershed imperviousness. We then model (EPA SWMM) drainage system-wide changes in flood risk given changes to wetland extent under these different development scenarios.
Results/Conclusions
We find that, across all relevant development scenarios, that loss of urban wetland area increases the number of locations in the drainage network that experience flooding, and increases the volume of flooding in locations presently at risk of flooding. Further, the effects of wetland loss are generally experienced “downstream” in the drainage network rather than “upstream.” Small losses to wetland extent, in the scenarios in which this occurred, tended to not produce substantial changes to flood location or volumes in the network, perhaps due to the effective “overdesign” of these spontaneous wetlands relative to their watersheds. In our model, scenarios that featured greater amounts of wetland loss tended to experience an increase in the number of flood locations and in flood volumes than did our scenarios that conserved or expanded wetland coverage. We demonstrate reduced risk of pluvial flooding in urban development plans that include wetland conservation and/or expansion.