Crazy,
A big concern with small ponds in small ravines is big rains. If the watershed area above your pond has any significant size, then even a moderate rain can supply more water than the capacity of your pond.
[/b][/u]If water goes over your little dam, then it will almost certainly take out your dam.[u][b] It is money well spent to size your emergency spillway to pass a 100-year rain so you do not have to rebuild your dam.
What is the area of your watershed? Is it mostly forest, grassland, or rocks? This will help you calculate how much water you will get from a big rain.
Finally, if the dam does wash out on your little pond, there is a good chance the surge of water and debris would also take out the dam on your lower "big" pond.
Despite all of my "dire warnings", I still think this pond is a good idea for your intended uses. You just need to plan appropriately before you start spending money on the project.
Good luck - Rod
