The Colorado never reaches the ocean any more (only exception was a few years ago when an earthquake damaged some of the irrigation canals on the Mexico side).
100% of the water of an average year is used by agriculture, cities, energy production, etc. The storage (ie reservoirs) in the Colorado basin is about 4-5 years worth of annual flow. Given that Mead and Powell are about half full, it would take a couple years of REALLY big runoff to fill all the reservoirs.
The only feasible way that it could reach the ocean again is by mandating that a certain amount flow through the Delta for "environmental" purposes. The US and Mexico are working on a treaty to do this, but it's a pretty complicated process. Here's some more about the new treaty: The United States and Mexico Can Restore the Colorado River Delta – News Watch