The two times I've been there (not this year), there was no getting a trailer in the water at all. If I recall correctly, you can back to within a few feet of the water but there's a sharp bank right at water's edge.
At about 1300cfs on May 10, my friend was able to get the back of his trailer into the water to load up his 14' NRS fully loaded boat. We were the first on the ramp that day so it was still dry and not slick as it tends to get after hit with water. It was a bit dicey but not too bad. I just put my trailer about 5' from the edge and man handled our two boats up there after unloaded.
I took out there April 25th @ 600cfs and there was no way a trailer could be backed in because of the drop off at end of ramp. - no way
Last successful trailer take out I witnessed was a group lowering the trailer with a heavy-duty front mounted winch, loading boat and winching back up and over "drop-off" and then attaching trailer to rear hitch.