Walipini concerns

I think the walipini style may be beneficial to my greenhouse but I have concerns about flooding. What preventative designs are there to control too much water? Would a drain to the outside let in cold winter air? I am in US zone 7.

You either need a drain to daylight (runs at a drain slope until it comes out of the ground downhill) or a sump pump.

The drain will spend a lot of its time 5+ feet underground so it will be tempered to 55ish degree earth temp, basically acting as a earth tube when it isn't full of water.  Good for summer chilling, too

Thanks R Scott, that's great info. My yard has a slight slope down to a creek about 30ft from where the greenhouse will be. I was only planning on digging down 2ft, so the drain would be like 2.5ft below the surface (our frost line is 18 inch s FYI). The location used to be a child's play area and I'm bagging up all the shredded tires now. I'm hoping that by going two feet down I can remove all the contaminated soil and be able to plant directly into the ground, but I'll have the soil tested to be safe.