I have gravel and fabric under mine, and I also dug a trench out of each individual run to a trench in the main run that flows to a ditch. All trenches are also full of gravel, topped with fabric, and everything is sanded. It's more work, but I don't have drainage issues even in heavy rain. I've read a number of posts from people who "just dumped" who have problems with water backup. Sand drains good, but once it hits capacity it can become just as bad as mud, so for my mind it's worth the extra work at setup to avoid flooding. Another strategy you can use instead of trenches is what's known as a "dry well." You can dig in a barrel (30 gal, 55, whatever) in a low part of the run, perforate the sides and surround it with gravel in the hole. Top it with more gravel, then fabric, then sand. Water will drain through the run to this location as long as your water table doesn't rise enough to fill the barrel from the bottom. Here in NE Texas dry wells work great, and take less digging (although deeper) and less gravel than a long trench. I chose the trenches because I have so many smaller runs I would have to trench to the dry well(s) anyway, and the ditch was already there. Either way, you need to provide extra drainage for heavy rain events. I know it's not the answer you wanted, but it's the one that will save you work in the long run.
We're about to see how well it does as we're in line for some strong storms tonight and tomorrow, but coming from Maryland and the beach areas, there is no way on this green earth that sand can be messier than the slop of mud that i call a chicken pen! Yes, sand gets wet, yes sand will retain moisture, but sand also dries much faster and the ground under the sand will still absorb the water as it soaks thru the sand. The only problem i have with sand is when it gets in my car and my bathing suit.
Thank you. Actually, that is my peafowl aviary. I have 4 peas that live in that aviary. The measurements are 28 feet long - 10 feet wide - 8 feet tall. And yes, the coop ventilates VERY well without drafts. They seem to enjoy it.
So far so good here. I've been wetting the pen every few hours today since it's so hot out. Although they want to stay inside mostly, i was just out to check since it's cooling off, everything looks pretty dry and not stinky!!