Excavation Rate of the Grand Canyon

In March, I went over the US on a holiday. One of the places we visited was the Grand Canyon. Like most, I was amazed at the size and depth of it. However, I’m a mining engineer who designs big holes for a living, so I was interested to know how the river excavated it, so I had at look at the information they had posted around. Two things struck me:

  1. The Grand Canyon is only about six million years old.
  2. The flow rate of the Colorado river hasn’t significantly changed in that time.

This set me thinking – if it’s only 6 million years old, and the river hasn’t significantly changed in that time, then how did the river manage to carve out the canyon, that seems like a lot of dirt to move per year. So like a good engineer, I thought I’d calculate it:

Volume of the Grand Canyon – 4.17E+12 m3

Years to excavate – 6,000,000

Excavation rate per year – 695,000 m3/year

Excavation rate per second – 0.53 m3/second

Half a cube per second sounded achievable, though possibly more dirt than a river might be capable of carrying. So I looked up the sediment carrying capability of water, and while it’s on the high side, definitely within the capability.

Half a cubic metre of dirt per second isn’t particularly high when compared to a lot of earth moving equipment these days, but when done every single second for the last 6 million years, it adds up to something amazing.

Volume Flowrate
4.17E+12 Volume of the GC
         695,000 cubes per year
             1,904 cubes per hour
                0.53 cubes per second 500 m3/s
                1.32 tonnes per second 500 tonnes per second