Few countries have to contend with water the way the Netherlands does. With 26% of its area and 21% of its population living below sea level, water control is critical. This satellite image shows some of the natural and manmade features that help protect the landscape. The West Frisian Islands, the long spine-like archipelago seen here, form the first barrier. Behind them lies the mudflats of the Wadden Sea, home to countless wetland species. The Wadden Sea is separated from the freshwater Lake Ijssel by the Afsluitdijk, constructed in 1932 to protect the country from rising seas. With the dam in place, the Dutch used wind power to drain the shallow lands behind the dam, reclaiming the polders labeled here. With the islands, mudflats, and lake between urban settlements and the sea, engineers have more options for diverting water and protecting people from disastrous flooding. (Image credit: A. Holmes/NASA’s Ocean Color Web; via NASA Earth Observatory)
Tag: civil engineering
How Sinkholes Form
Growing up in the Ozarks, I explored my fair share of caves and sinkholes. These geological features form when flowing groundwater erodes soil, sand, and even rock underground. The Ozark Plateau consists largely of limestone, which is water soluble, making it very prone to this internal erosion. As bedrock dissolves away, it is eventually unable to hold up the weight of ground above it, causing a catastrophic collapse into a sinkhole. Although my childhood sinkholes were naturally occurring, they can also form in spots where leaking pipes and infrastructure help wash underlying soil away. Unfortunately for engineers, this internal erosion can take place for years without any visible sign above ground. (Image and video credit: Practical Engineering)
How Sewers Work
One of the most important and underappreciated pieces of urban infrastructure is the sewage system. We rely on them to make our waste vanish, as if by magic. In reality, these systems are carefully engineered and built to be largely self-cleaning and future-proof. Gravity is the primary driver of the system, and engineers design the slope of sewage lines so that flow inside the pipes is fast enough to keep solid waste suspended. There are, of course, plenty of challenges involved; check out the full video for an overview. (Image and video credit: Practical Engineering)
Tokyo 2020: Kasai Canoe Slalom Course
The Kasai Canoe Slalom Course is Japan’s first man-made whitewater venue. To test the design and its multiple configurations, engineers at CTU in Prague built this large-scale hydraulic model. Check out the video below to see it under construction and in action.
The course is adaptable so that it can be used for high-level competitions like the Olympics, then reconfigured for recreational use. You can even see what it’s like to run part of the course in a multi-person raft, thanks to a miniature, GoPro-equipped boat! (Image credit: top – M. Trizuliak, others – CTU Prague; video credit: CTU Prague)
Missed our previous Olympics coverage? Check out how sailboats outrace the wind, the future of swim tech, and how surface roughness affects volleyball aerodynamics.
Pump Problems
Pumps are a critical piece of infrastructure, but to keep them operating, engineers have to account for several potential pitfalls. In this Practical Engineering video, Grady discusses some of the common fluid dynamical effects that can destroy a pump and its performance. As you’ll see in the video, a lot of the challenges boil down to keeping air out of the pump. Since air and water are vastly different in their density and compressibility, most pumps cannot handle both of them at the same time. Pumps need to be primed to displace any air inside them and allow them to develop the suction needed to pump water. On the other hand, too much suction can create cavitation, which damages pump parts. And, finally, the intake systems for pumps have to be designed to keep air from getting sucked in. If nothing else, having too much air in the lines reduces the pump’s efficiency. (Image and video credit: Practical Engineering)
Pipe Flow and Pressure
Whether you’re a homeowner or an engineer, at some point you’ll have to deal with pipe flow and the challenges inherent to getting water from Point A to Point B. This Practical Engineering video provides a great basic overview of pipe flow and pressure loss, whether you’re looking for an introduction to the topic or a little refresher. It’s also got some small-scale demos in an actual system to help you build intuition for what changing pipe length, diameter, and fittings does to the flow. (Video and image credit: Practical Engineering)
Where Does Stormwater Go?
Stormwater management is one of the biggest municipal challenges towns and cities face. Urban surfaces are largely impermeable, preventing rainwater from soaking into the ground. Instead roads, ditches, and channels collect water and, typically, divert it as quickly as possible into natural waterways.
In contrast, wild landscapes tend to slow water run-off, filtering it into the water table, soaking it up with vegetation, and distributing it across a larger area. Recently, cities have started using low-impact development strategies, like rooftop gardens and rainwater collection, to mimic natural landscapes in urban ones. (Image and video credit: Practical Engineering)
Protecting From Storm Surge
The most dangerous and destructive part of a tropical cyclone isn’t the wind or rain; it’s the storm surge of water moving inland. This landward shift of ocean takes place because of a cyclone’s strong winds, which drive the water via shear. The depth storm surges reach depends on the wind speed and direction, shape of the shoreline, and many other factors, making exact predictions difficult.
Fortunately, engineers can — with enough foresight and investment — build structures and networks to help protect developed land from storm surge flooding. (Image and video credit: Practical Engineering)
Coastal Erosion
The same dynamic forces that make coastlines fascinating create perennial headaches for engineers trying to maintain coastlines against erosion. This Practical Engineering video discusses some of the challenges of coastal erosion and how engineers counter them.
In a completely undeveloped coastline, waves and storms erode the shoreline while rivers and currents replenish sand through sedimentation. Manmade structures tend to strengthen erosion processes while disrupting the sedimentation that would normally counter it. Beach nourishment — where sand gets dredged up and deposited on a beach — is an engineered attempt to replace natural sedimentation.
Dunes, mangrove forests, and wetlands are all nature’s way of protecting and maintaining coastlines. We engineers are still learning how to both utilize and protect shorelines. (Image and video credit: Practical Engineering)
Permeable Pavement
Controlling storm water is a major challenge in urban environments, where many surfaces are impermeable. In a city, rain cannot simply soak into the ground and filter into the water table. One potential solution is permeable pavement, which uses the same ingredients as its common counterpart minus the sand that usually packs into gaps between the gravel. Without the sand, the final pavement allows water to soak through, as seen above. In practice, the water sinks into a porous reservoir beneath the pavement that helps store and regulate the water’s discharge into the soil.
Unfortunately, this solution has its limitations. Permeable pavement is not as strong as the regular variety, so it doesn’t work for highly trafficked areas like roadways. It’s also not well-suited to colder areas, where freezing and thawing may disrupt its operation. But it is another tool in engineers’ toolboxes when it comes to keeping urban environments in harmony with nature’s needs. (Image and video credit: Practical Engineering)
