Levees or Wetlands on a Sinking Coast
A coastal city of 120,000 people sits behind a levee system that engineers rate for a 100-year storm. The land beneath parts of the city is sinking about 8 millimeters per year, while sea level is rising. A 2021 hurricane pushed a 4.5-meter storm surge against the levees; the city evacuated 70,000 residents, but many low-income households lacked cars. The state proposes two options: spend $2 billion to raise levees by 1.5 meters, or spend $1.2 billion to restore 40 square kilometers of coastal wetlands and raise levees by 0.5 meters. Wetlands can reduce surge height, but restoration takes decades. The city council must choose a strategy for the next 20 years and asks for a geographic analysis of physical and human systems. A federal grant also requires an equity review.
1. Explain how subsidence, sea-level rise, and wetland loss interact to increase storm-surge risk in this city.
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Subsidence lowers the land surface relative to the sea, and sea-level rise raises the water surface; together they increase relative sea level and reduce the effective height of the levees. Wetlands act as a buffer by absorbing and slowing surge, but wetland loss removes that friction and allows deeper water to reach the city. The interaction is cumulative: as land sinks and wetlands disappear, the same storm produces a higher surge at the levee, while the levee's protective margin shrinks. Restoration can help over time, but because wetlands take decades to grow, it does not replace immediate levee protection. The city faces a moving baseline, not a fixed 100-year risk.
2. Compare the two options using at least one physical and one human-system criterion.
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Physically, raising levees 1.5 meters gives immediate protection against a higher surge, but it does not address subsidence or lost wetlands, so the margin will shrink again; wetland restoration plus a 0.5-meter levee is slower and may not protect against a major surge in the near term, though it reduces surge over decades and provides habitat and flood storage. From a human-systems view, levee-only spending may protect property but leave low-income households without cars exposed during evacuation; wetland restoration may offer broader long-term benefits but could displace or restrict land uses. Equity review should ask who gets protection first and who bears disruption. A hybrid may be safer than either pure option, but it costs more and requires long-term maintenance.
3. What geographic data would you request before recommending a choice, and why?
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I would request high-resolution elevation and subsidence maps, because levee height relative to sinking land determines actual risk. I would ask for storm-surge and wetland-change models under different sea-level scenarios, since the 100-year rating may be outdated. I would also need demographic and evacuation data: where low-income, elderly, or carless households live, which routes flood, and where shelters are. Land-use and wetland ownership data would show where restoration is feasible and who is affected. Finally, cost and maintenance projections would test whether the city can sustain each option. These data connect physical processes to human vulnerability and help the council avoid choosing a levee height that looks safe on paper but is overtaken by subsidence and sea-level rise.