Lake Powell’s Effect on Cataract Canyon

Cataract Canyon is 41 miles long. It starts at the confluence of the Colorado and the Green Rivers in the heart of Canyonlands National Park.

While there has never been a final agreed number of rapids in Cataract, what has always been agreed upon is that Cataract’s rapids are fearsome and worthy of respect.

The 41 miles of Cataract start at an elevation of 3,875 feet above sea level and drop 410 feet through the river’s descent to River Mile 175.

When filled to 3700 feet above sea level (full pool), Lake Powell inundates Cataract Canyon up to River Mile 203. Only 14 miles and 23 rapids of Cataract are not affected by Glen Canyon Dam. When the lake is at full pool, only 35% of Cataract remains.

In terms of river gradient and reservoir capture: Glen Canyon Dam can impound water from its base, which is approximately 3,135 feet above measured sea level (famsl), up to a targeted managed height of 3,700 famsl. Cataract Canyon’s descent ended at river mile 175.5 at an elevation of 3,465 famsl. The difference between 3,465 and 3,700 famsl equates to 40% of the gradient contained in the reservoir, but over 50% of the water storage capacity.

It is worth noting that the minimum power generating level at Glen Canyon Dam is 3,490 famsl. This is historically the base of Cataract Canyon’s Dark Canyon Rapid.