There’s a general scientific consensus that sea levels are rising and that rainfall will probably increase over the course of the coming century. If temperatures go higher, it seems almost sure that that will happen. Glaciers will melt, and higher evaporation will drive more frequent storm systems inland. 

City planners, therefore, are thinking carefully about their flood defense systems. The vast majority of the world’s major urban centers are located right next to either rivers or oceans, meaning that they’re directly in the firing line. If predictions turn out to be accurate, millions of people could become displaced.

Urban planners, therefore, are turning to the latest science to figure out how to defend their populations from water incursions. So far this century, we’ve seen various attempts to keep the water back, but they’ve not been particularly successful. Examples from both the US and Europe show that when flooding occurs, it’s almost impossible to protect property. 

Currently, a lot of cities operate a cost-benefit system. Many now have the ability to dam watercourses flowing through their centers, saving high-value real estate in the middle at the expense of low-value land in outlying regions. 

This tactic, however, is becoming a little long in the tooth. As flooding becomes worse, simply holding water back will no longer be an option. Groundswell, surface run-off, and drainage overload remain significant hurdles. 

Cities worldwide are currently scrambling to figure out what they can actually do to mitigate the problem. Yearly flooding simply isn’t an option, even if it is predictable. This isn’t ancient Egypt. The modern world is surprisingly dependent on “dryness.” 

Computer Modelling

The first step is to try and figure out how precisely flooding problems occur. Many city planners currently have no idea how a flood situation might evolve, so they don’t have effective strategies to mitigate it. And because of that, they have no idea where to direct funds. 

Computer modeling, however, is trying to solve that problem. Engineers are investigating things like topology and fluid dynamics to work out how flooding might interact with a city's features. The main goal is to figure out the likely course of the water if it breaches existing defenses. They need to work out where it will create problems first, and how that might have knock-on effects on the rest of the city. 

The beautiful thing about data modeling is that it allows you to create prediction scenarios to get an idea of how frequently catastrophic events are likely to occur. Most planners are willing to accept a major breach every one hundred years. Still, relatively few will take anything less than that. The risk to the urban environment is too high. A once-in-a-century event is costly to mitigate. But dealing with a breach every ten years will likely cause even more considerable damage. 

Combining data from historical trends lets planners do better cost-benefit analyses. They can calculate how much they’ll need to spend on flood defenses and compare them to the likely savings. Financial forecasts can then become meaningful, allowing them to make the best use of tax money. 

City resources are typically minimal. Some jurisdictions have a lot of money, but most have to make do with whatever funds local residents can generate. And if that’s not much, then cities themselves can fall into disrepair. Therefore, keeping the cost of flood defenses low will remain a substantial policy objective on many town councils. 

Shoring Up Natural Defenses

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Most cities benefit from natural defenses against flooding. When early settlers chose locations, they typically found stable areas of land that didn’t wash away their mud huts, every time there was a rainstorm. Most modern metropolises, therefore, are beside high-banked rivers or natural harbors that protect against storms. 

With that said, the world is changing, and the severity of storms in some places means that natural defenses aren’t sufficient. They simply can’t contain the increase in the volume of water. For this reason, cities have to invest in shoring natural defenses to protect them as water levels rise across the board. 

Interestingly, though, we don’t see widespread evidence of ocean levels rising in the short term. Despite the predictions of the early 2000s, the world’s coastal cities have not been inundated with saltwater. To the naked eye, there’s no difference in sea level. 

This fact isn’t just a feature of western coastlines – it’s also borne out by Pacific Atolls. Many researchers believed that these low-lying areas of land would eventually disappear beneath the waves, but that doesn’t seem to be happening. Whatever is going on in the climate right now, we do not see many of the predictions come to pass. 

For city planners, it is good news. It might mean that sea-level change happens much slower than many imagined. This added time gives them much-needed respite to effectively improve coastal defenses and dredge rivers so that they have more capacity. 

Modifying The Drainage System

Cities can usually cope well with rare storms. But if they don’t, the draining system often winds up being the weak link in the chain. Roads flood because subsurface waterways can’t cope with the volume of fluid traveling through them. 

Over the next few decades, we’re likely to see engineers attempt to widen existing courses to channel water downstream faster. Systems from the 20th-century probably won’t suffice. They need to be bigger and better. 

Expect, therefore, to see engineers clambering in and out of Amercast manhole covers. City streets will require ripping up and new pipelines placing, especially if urban sprawl continues over the coming years. 

Building On Higher Areas

Cities should be building on areas of land that are higher up and further away from bodies of water. Unfortunately, the vast majority of cities are currently doing the opposite. Flood plains tend to be flat, so building on them is cheaper. 

This approach, though, is short-term thinking. While it might bring down property prices today, those homes aren’t going to be worth much in the future if they’re always being flooded. 

Therefore, city planners are moving actively in the direction of trying to encourage construction on elevated land, usually some distance from the city center. In the process, they have to construct new, innovative transport links to keep everyone connected. The future city environment could look more like a collection of build-up nodes than urban sprawl, depending on the area's topology. 

Texas A&M University recently conducted research in south Florida to see what effect rising sea levels could have on the roads in the area. Their study revealed that saltwater inundation could cause billions of dollars of damage and make some settlement inaccessible. Pumping the water out, though, resulted in overall cost savings in the long-term.

Therefore, the message for city authorities is clear: investing in flood defenses is still worth it, even if flooding occurs every year. Pumps can remove excess water and prevent it from damaging essential infrastructure. 

Micro Grids

Flooding has the unfortunate effect of shutting down power supplies and leaving people without energy. Downed pylons and flooded fuse boxes cut off electricity supplies, interrupting normal life. 

Therefore, cities are looking at microgrids to help them mitigate the damage of superstorms. They know that they’re not going to defend themselves against every rain cloud that comes their way entirely. But they can make themselves more resilient if a weather system overwhelms their flood defense. 

Microgrids are essentially areas of the power network that can work independently of the main gird. Usually, community solar projects power them, but they can also derive energy from geothermal and diesel generators. 

New York, for instance, already employs one of these systems to protect its food distribution system. If the power goes out at Hunts Point, the backups kick in immediately and continue to provide service. 

Rain Gardens

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Cities are also trying to make their environments more forest-like to reduce run-off. Rain gardens, many hope, will increase the time between the storm peak and flood peak.

For cities, spending money upfront on flood mitigation technologies is a political risk. Most residents aren’t thinking decades in the future. With that said, stormwater damage is often so severe that it can bring a city to its knees quickly. Policymakers, therefore, need to act fast and use the tools at their disposal to get the job done. 

City councils are already seeing the payoff on systems built fifteen or twenty years ago. Experts estimate that the Portland, Oregon, flood defense network saved the city millions of dollars worth in that time, recovering the initial cost of the investment. 

Cities all over the world need to prepare immediately for rising river and sea levels. Getting the jump on climate change puts them in a much better position to mitigate the damage when the storms finally arrive. Green infrastructure projects are cropping up all over the place as local governments attempt to deal with the problem of sewer overflow. The savings are substantial, but it is just a question of convincing people that it is worthwhile. We now have the science to make it happen. 

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