Coastal Floodplain Planning
A coastal town of 18,000 residents must update its comprehensive plan. About 240 homes sit in the 100-year floodplain; 40% of those households are renters, and the median household income in the floodplain is $38,000, compared with $61,000 townwide. Regional projections estimate 30 cm of sea-level rise by 2050 and 1.2 m by 2100. The town has three options: build an $18 million seawall that would protect about 180 homes; restore 60 hectares of wetlands for $4 million, which would reduce storm surge by an estimated 15%; or adopt a managed-retreat policy that buys out repeatedly flooded homes and downzones the floodplain. The town's annual capital budget is $22 million, and a federal grant could cover 65% of the seawall but not the wetland project. The planning commission must recommend one option to the town council next month.
1. Evaluate the three options using cost-benefit analysis, distributional equity, and geographic concepts.
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Start with scale and time. The seawall has the highest gross cost, $18 million, but the 65% grant leaves about $6.3 million local. It protects about 180 homes, or roughly $100,000 per protected home gross and $35,000 local, before maintenance. It may also create a levee effect: development feels safer behind the wall, and erosion may worsen nearby. The wetland project costs $4 million, protects fewer homes directly, and delivers broader benefits such as habitat and surge attenuation, but a 15% surge reduction is modest against 1.2 m of rise by 2100. Managed retreat addresses repeated loss and long-run risk, but buyouts often favor owners; renters, 40% of the floodplain, may lose affordable housing and receive nothing. The commission should compare options by risk reduction per dollar, who bears cost and benefit, and whether the option is adaptable as projections change. A hybrid of wetland restoration, targeted buyouts, and stricter floodplain zoning is more defensible than a single structural fix, especially because the seawall may be obsolete by 2100.
2. What additional data would you request before voting, and how would it change your recommendation?
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Request parcel-level elevation and repeat-loss records, not just a floodplain label; storm-surge and sea-level models at the town's scale; the grant's maintenance and cost-share conditions; the local cost of buyouts and the availability of replacement housing; and data on renters, incomes, and property values. The commission also needs to know whether the seawall protects the same 180 homes under the 2100 scenario or only under current conditions. If elevation data show that a subset of homes floods repeatedly, targeted buyouts may be cheaper and fairer than a wall. If the grant covers most capital cost but leaves the town with large maintenance obligations, the seawall's apparent local cost is understated. If replacement housing is scarce, managed retreat without rental protections could displace low-income residents. The recommendation should therefore be conditional and phased: fund wetland restoration now, commission parcel-level modeling, and pair any retreat with rental housing protections.