My head too. New spillway, next o the damaged one. Then, maybe, a complete replacement of the damaged one so that it can serve as an emergency spillway instead of the present system of overtopping a wier.
Even better.
How about atop the existing spillway? Construct it as you would an elevated highway causeway with piers, and then tie the new section into the old just a ways downstream of the spillway gates. Basically an elevated flume.
An added feature would be that you wouldn’t have to worry about underslab drainage. Any leakage would simply dribble into the remains of the old spillway below. Just make sure there’s adequate support into bedrock with the piers.