Hi, the flapper is just to keep the bugs in the skimmer. It does not do a thing to keep the waves out. Be careful with the water level also, much below the halfway point and you run the risk of creating a wirlpool effect that will draw a lot of air into your system.

Another use for duck tape to add to my list. The only things I have seen used are a rubber plug inserted into the center opening of the lid and a rock or two on the lid to hold it down tighter.

Aside from that, work on the landscaping and enjoy how much fun the kids are having.

Dennis