After looking at your pictures It looks like you have an excellent location for a pond. I can only think of one possible problem that might occur and that would be for the pond to leak. I would make sure that they do a deep trench across the creek with that track hoe and make sure they get rid of any gravel that would keep the pond from holding water. Your best friend against siltation is vegetation and if you want to keep things looking natural it can't be beat. Try not to allow any of your soil to become barren that is above the pond. Choose plants that have deep roots that can withstand a lot of water during a flood and plant them in the dry creek bottom. I have several large cottonwoods in the creek bottom above my pond that trap an enormous amount of sand when it rains. Something else you might do is to put any large boulders that are dug up during construction in the creek bottom abouve the pond. You are going to have a beautiful pond!