1. Sea level rise is only part of the story. Although it is a very real danger for cities in coastal plains, the worst-case scenarios in the next hundred years predict only six feet of increase. (This is more than enough to swamp millions of dwellings, offices, and essential infrastructure corridors, fundamentally changing the way cities operate.) However, the effects of sea level rise pale in comparison against increased storm surge. Intensification of coastal storms increases wave energy and its impact on structures; on top of sea level rise, surge will add 17’-28’ of swirling, turbulent water at rapidly decreasing intervals. These unpredictable storms raise the consequences and pose severe design challenges in coastal areas. At the same time, the episodic nature of these storms inspires debate about where and how much to defend, or what may be sacrificed.
2. Individual solutions don’t work. A single community cannot fight the battle alone. Water is sneaky – it laps around the back of a seawall or squeezes through an opening. It ricochets off hard surfaces, to rebound with double the force, caroming into whatever stands nearby like a frictionless billiards ball. When wealthy landowners banded together on the Jersey Shore to protect their fronts, they were surprised by water from their flanks. If Manhattan armors its tip, New Jersey and Brooklyn had better watch out.
3. We can’t continue to flood the powerless. As places design ways of living with water, those with resources will continue to have multiple options, while those with few resources will need assistance with the full range of solutions including elevation, retreat, and armoring. As these techniques become more prevalent, their cost will be built into the cost of building along coastlines, but right now, the added costs are a burden for many long-time homeowners in modest communities. In order for communities to remain whole, policy-makers must find ways to resist economic sorting at the water’s edge, but also to help them prepare for the challenges.
4. Coastal defences won’t stop all flooding. Coastal communities are trapped between two threats: rising sea levels and storm surge from the water’s edge, and increased stormwater flooding from upland communities, new-paved and impervious. The coastal watersheds are the meeting place of these conflicting systems. One set of tools, useful though they may be, won’t solve the full range of issues. Water from rivers and upland flooding requires storage capacity, but there is no bowl big enough for the ocean’s surge. One notable exception: the Thames Barrier has recently refined its operation, releasing water during low tides and closing before storms and high tides, to allow for more storage capacity from rains. In most cases, two separate but complementary toolboxes are necessary.
5. Cities (and people) need continuity. Interruptions cost money, and as more events occur, utilities must be reliable to keep people safe, transportation links active, and communications underway. This means decentralized, redundant, and self-sufficient options for power, potable water, and wastewater treatment. Failsafe. Uninterruptible. Dependable. When a person loses power for days, refrigerated food is lost, toilets don’t flush, and the potential effects on health are disastrous. When a city loses power for days, business shuts down, mobility is halted, goods don’t get produced or distributed, and financial capital shrinks. The consequences at both scales are potentially significant. It is the responsibility of cities to provide the essential services for continuity, and reduce interruptions.