How to build a water overflow reservoir
I will be building a new home and have to do a lot of excavation so I am thinking of creating a reservoir that could be used to hold back excess water during downpours. This would then enable me to bring along a lot of my special wet/swampy area plants, like Joe Pye, Goats Beard, Milkweed, Cardinal Flower, etc.
The area will be dry woods so without a wet spot, I won't be able to have my favorites. I can create a fairly large structure if needed, about 250 sq ft or so.
Can anyone give me tips on how this is done?