NyQuiLlama,
I just got on the site this week and read with interest about your culvert removal project. Sounds like you got your main problems with leakage solved, and you indicate the new spillway is working okay. I'm under the impression that your new spillway is just an earthen trench off to the side of the dam. If this is the case, make sure that you have a good sod-forming grass covering the spillway to prevent erosion, during heavy rain events.
However, it sounds like you have a constant flow of water through your dam, and in this case just a grass covered spillway isn't the best solution, as the constant flow of water will gradually erode into a channel that will get bigger over time. If that is the case, you will want to protect that earthen spillway by "armoring" it with rock. I'd even suggest putting some plastic erosion control sheets beneath the rocks. You will want to use some larger size rocks in some places to prevent a heavy flow of water from washing them away. Remember that flowing water has a tremendous amount of power.
