More complete answer: the features of the Grand Canyon are not the features that are produced by a flood release, rather they are features that are produced by slow erosion and which are destroyed during flood release.
If you want to see what ancient evidence of massive flood release looks like google "channeled scablands"
Geologists (real ones) do know what flood erosion looks like, they do find evidence of it in various places, but they all come from different times in different places.
The features of the Grand Canyon, on the other hand, are evidence of slow erosion, leaving meandering channels, and pillars and other features that would be eroded by flood flows.
This: google maps arial view of the Grand Canyon is not flood released erosion: there are too many meanders, too many side branches contributing to the river from the sides (perpendicular to any flood flow) and too many spires and towers left behind that are total acharacteristic for flood release flows.
There are also other geological formation of the same age and in the same region as the Grand Canyon that could not have survived a flood release -- such as the "voodoos" in Bryce Canyon and this part of Goosenecks State Park.
For a longer answer, study geology. From geologists. You don't have to take my word for it.
