I'll express sympathy. Sorry that your pond is getting filled with silt!
Looking at your pics, it appears that the forest soil is probably a clay-silt. I believe that means you are going to have to undertake a fairly large endeavor to solve the problem. For any temporary obstruction that you create, the running water is going to erode a path through your soft soil and send the muddy rain water right back to your pond.
How large of a pipe or culvert would it take to convey all of the water in that creek due to a 4-5" rain? I think that will be the factor that controls your solution.
One solution is to build an actual dam for that creek that will NOT be overtopped during a big rain event. However, if you are building a dam, then you might as well build a pond. It would be nice to have an upper pond, but that tree-covered slope does not look like a great place to build a pond.
Another solution that might be relatively cheap, would be to rent a little excavator and create a bypass for the creek. It would go around your pond and deliver the water to the same place your current pond outlet delivers water. However, in your pictures, it appears you have a high bank around your pond. Excavating a long trench 3' deep is relatively easy, but doing one 10' deep is a whole different job, and the sides will cave during fast water flows.
Can you intercept the creek higher up the slope and build a diversion ditch around your pond? That might work if you have a good route.
If the maximum water flow is only the amount of two 6" pipes, then you could make a small diversion dam at a higher elevation for the creek and run two lengths of corrugated 6" drain pipe around your pond and deliver the storm water below your main dam. (However, I suspect your stream flow is larger than that.)
Do you want to clear some timber in your woods? If you created some clearings and uniformly graded the slope, then you might be able to establish a few bands of thick grass. That would not be a 100% solution, but you might be able to significantly reduced the silt load going into your pond.
Finally, I guess you could build a "clean out peninsula" in your pond and an underwater berm to contain the delta of silt that builds from your creek entry point. If you keep the silt in place, you could clean it out every few years with an excavator.
Sorry for not having any good solutions. Just throwing out some ideas so you can see if you can fashion a solution that fits the actual conditions that you can observe on the ground. Hopefully, someone else drops in with some better ideas.
Good luck on your project. A 2-acre pond in the woods is a beauty that you need to take good care of!
