Arches & Dams

I ran on the historic railroad trail in Vegas last week, which connects to the Hoover Dam, an engineering marvel built on the Colorado River. I was zoned out at that time due to tiredness and couldn’t really soak in the complete experience of viewing the Hoover Dam with my own eyes (story of my life lately). But I know 19-year-old me would have nerded out on the structural engineering technicalities behind the dam's famous arched wall. Back then, I was in school pursuing a degree in Civil Engineering and had aspirations to work in the research side of structural or geotechnical engineering.

That Civil Engineering degree taught me that arched structures are not just for aesthetics; they have a strong engineering basis that supports their usage. Now it has been more than seven years since that phase of my life (guess I’m old now), so all details are hazy in my mind. I googled a little bit to jog my memory and decided to put my limited knowledge and understanding of arches in writing.

Say you apply a load on a straight and flat structure (imagine pressing at a specific point on an ice cube), you can cause the structure to break at that point, provided the load is greater than the strength of the material used in that structure. When you manage to curve (or arch) the same structure, and apply the load at a specific point (imagine arching a book and pressing on it), the arch tries to flatten itself by pushing its edges outwards.

Now, say you manage to lock these edges by putting the arch between two sturdy walls. When the arch pushes its edges outward into these walls, the walls will push back with equal force in the opposite direction (Newton’s third law of motion). So in a way, walls are squeezing the arch and strengthening it. Since we humans are suckers for efficiency and cost reduction, we managed to link the dots that we can compensate for using less material in a structure by just arching it to maintain an acceptable level of strength. Arched dams were born out of this idea.

This could be an oversimplification, but think of dams as huge vertical concrete blocks (or sometimes made up of soil and earth), born out of the human desire to control water flow and harness it to generate electricity. When a massive volume of stored water presses against that block, the structure needs to be strong enough to withstand the resulting pressure without crumbling. This led to the idea of gravity dams, where the solution is to make the dam heavy enough so the water cannot topple it. Naturally, this requires enormous amounts of material and time to construct.

But consider a river flowing through a narrow canyon between two massive natural rock formations. Instead of a flat vertical block, what if we curve the dam and anchor its edges into those canyon walls? When water presses against the curved face, the load gets distributed along the arch and transferred to the canyon abutments, which push back in response. This allows the structure to achieve the required strength using less material, reducing overall cost. The design of Hoover Dam uses this idea to some extent. Its curved form is anchored into the rocks of Black Canyon along the Colorado River.

The Romans were one of the first humans to adopt this arch dam idea several centuries ago, and it is amazing how this timeless engineering is still being used in the modern world.

On a slightly unrelated note, arches also teach us that it’s okay for our life journey to curve away from a linear straight line. When life eventually starts adding those difficult loads on you, you can find extra strength in that arched path of yours!

Colorado River in Black Canyon