The "emergency Spillway" is actually not a spillway and it does not have an valves or any control son it. It is actually an emergency overflow and consists of a very long concrete berm that starts at the north end of the main spillway structure and goes a few hundred feet north to a hillside. At the spillway structure end, it is a tall berm that does look a bit like a concrete dam, but at the north end it looks like a concrete curb with level, or nearly so, ground on both sides of it and it's maybe 6" high, one can easily walk over it--in fact the road to the boat launch area does go over it. The top of the berm is one foot above the highest water level the dam normally holds. The main spillway can let water out quite a ways below the "full" mark--they are trying to get the dam 50 below the full point, so I know the spillway can let water out that far down.
The Emergency overflow is a "worse case" scenario thing, to save the main dam just in case more water comes in than they can let out. With the damage occurring to the main spillway, it was turned off and then the water into the dam overcame what they could control, and the water went over---it was a foot and a half ABOVE the emergency overflow berm. That is a HUGE amount of water, but still less than 100K GPM, which is what they are sending down the main spillway now, and the water is slowly going down. During the rainstorm it was estimated that as much as 180K was coming into the reservoir, but that is now down to 39K, so the water is going down now..I have seen as much as 180K go down that spillway without it failing; the initial failure was not caused by excessive water flow.
Normally, they can also run water through the powerhouse to help control water level, but the debris that has come down with the various failures has clogged the bottom of the river, so the water is now too high in the river to allow them to send water through the generator turbines. This also added to the initial problem of not letting enough water out.
We are still in danger if a large storm comes in. Right now the current storm has been greatly downgraded, so we should be OK this week.
While it has been reported that the evacuation order has been lifted, what was actually changed is the evacuation is no longer mandatory, and is now an evacuation warning; i.e. be ready to leave at a moment's notice.