Although they’re iconic, arch dams like the Hoover Dam are relatively unusual. In this Practical Engineering video, Grady looks at the forces a dam needs to withstand and where and why an arch dam is useful. It’s a good reminder that even water that (for the most part) isn’t moving is still a challenge to deal with. (Video and image credit: Practical Engineering)
Dams are critical pieces of infrastructure, but, as Grady shows in this Practical Engineering video, they are destined to be temporary. The reason is that they naturally fill with sediment over time. Rivers carry a combination of water and sediment; the latter is critical to healthy shorelines and stable ecology. But while sediment gets carried along by a fast-flowing river, slower flow rates allow sediment to fall out of suspension, as demonstrated in Grady’s tabletop flume. As his river transitions to a deeper, slower-flowing reservoir, sand falls out of the flow, building up colorful strata. The sand and water even create dynamic feedback loops, as seen with the dunes that form in his timelapse and march toward the dam.
Any long-term plan for a dam has to deal with this inevitable build-up of sediment, and, unfortunately, it’s not a simple or cheap problem to address, as discussed in the video. (Video and image credit: Practical Engineering)
Managing an electrical grid is all about balancing the electricity that plants can supply with the instantaneous demands of consumers. If there’s more power available than people need, it needs to get stored somehow. And for decades, the best way to store that excess supply has been in hydroelectric reservoirs like at the Taum Sauk Dam. These facilities pump water to a reservoir at a higher elevation when there’s extra electrical power available, and, when more power is needed, release that water to run through hydroturbines.
But storing water atop a mountain comes with unusual challenges for dam, and the 2005 failure of the Taum Sauk Dam facility highlights some important lessons for engineers. As Grady lays out in this Practical Engineering video, there was no single mistake that led directly to the dam’s failure. Instead, post-collapse investigations found a series of seemingly minor issues that, together, led to catastrophe. It’s well worth watching, especially for engineers; we could all use an occasional reminder that a “quick stopgap measure” isn’t enough. (Video and image credit: Practical Engineering)
Dams often use fish ladders to help migratory species make their way upstream without interruption. In this video, Grady from Practical Engineering discusses some of the considerations that go into this special infrastructure and what kinds of designs work for different species. The first challenge for any dam is attracting fish to the ladder, which is often done by regulating the water flow at the entrance to create the velocity and turbulence that fish look for when going upstream.
Once fish are in the ladder, they travel up a series of jumps that break the dam’s elevation into manageable steps. Different dams use various baffle designs to create jumps suited to their local species and the way they like to swim. Calmer spots in each section give fish a spot to rest before they carry on. In well-designed systems, the vast majority (97%!) of fish that enter a ladder make it through to the other side. (Video and image credit: Practical Engineering)
Many dams in the U.S. were built at a time when their ecological impact was not a major concern. But, thanks to ongoing efforts to study affected species and upgrade infrastructure, many dams now balance human energy needs with the needs of non-humans, like migratory fish populations. In this video, Grady from Practical Engineering takes us behind-the-scenes at McNary Dam in the Pacific Northwest, where special plans and equipment help adult fish swim upstream and juvenile fish pass downstream with as little impact as possible. It’s impressive just how widespread and thorough their infrastructure for letting fish and lampreys through is! There are even facilities to help naturalists track and study the populations passing through. (Video and image credit: Practical Engineering)
Dams and reservoirs need a way to control their water level, and for many, that’s managed using spillway gates. In this video, Grady from Practical Engineering introduces several types of spillway gates, including their advantages and disadvantages. As always, he’s got neat tabletop demonstrations of each type, and he digs into the practical issues engineers face when building, maintaining, and repairing these critical pieces of infrastructure. (Image and video credit: Practical Engineering)
Groundwater can sometimes wind up in unexpected places, given the way it interacts with subsurface structures. In this Practical Engineering video, Grady discusses the paths that groundwater takes around structures and how civil engineers account for groundwater-related forces on dams and other buildings. As always, he illustrates with excellent model demos, allowing viewers to see groundwater interactions for themselves. (Image and video credit: Practical Engineering)
Hydrostatic pressure in a fluid is based on the fluid’s depth. You’ll rarely see a more dramatic example of that power than with a water release from a dam. Here we see the outlet of the Verbund Hydro Power dam in Austria. With 190 meters of water behind the dam, the outlet jet is massive. It moves 20,000 liters of water per second at a speed of 50 meters per second. Imagine what it would be like to stand next to that! (Image and video credit: Discovery UK; submitted by Olwyn B.)
The Glen Canyon Dam lies on the Colorado River, upstream of the Grand Canyon. Because the dam blocks sediment from upstream, the region’s only sediment sources are two tributary rivers downstream of the dam. Periodically, the Bureau of Reclamation releases high flows from the dam in order to mimic the seasonal floods that existed on the river before the dam was built. These surge flows pick up hundreds of thousands of tonnes of sediment from the tributary rivers and push it downstream, creating and renewing sand bars and beaches along the Colorado. (Video and image credits: Bureau of Reclamation, 1, 2)
Human infrastructure like dams have the challenge of standing up to whatever nature can throw at them. It’s expensive, if not outright impossible, to build to every single contingency, so engineers have developed methods of dealing with problems like excess flow caused by a storm. For dams, one of the ways of dealing with this are spillways, which allow a method of controlled release from a reservoir.
Spillways come in many shapes and sizes, as seen in the video, but there are two general types: those that are actively managed and those that are automatic. An automatic spillway is like the “morning glory” type seen in the middle animation. There’s no on or off for a spillway like this. Instead, once the water level is high enough, water naturally flows out. In that sense, it’s like the overflow holes found in many bathroom sinks.
Controlled spillways are usually managed with gates that can be opened or closed as operators need them. This technique gives more granular control and can even end up being cheaper in some situations because it requires less space to implement. (Video and image credit: Practical Engineering)