My recommendation would be to pump the water down to where you're below the spillway and get down there to patch it as well as possible. It's going to be very difficult to patch with water still flowing, especially if the leak is relatively large.

You can rent pumps from most rental places, or find one on the cheap on craigslist like I did.

Dale

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"When tempted to fight fire with fire, remember that the Fire Department usually uses water." - anonymous