A drainage system is needed if you're going to use substrate. A chameleon enclosure needs to be misted several times a day to keep up the humidity and believe, humidity will drop even if you have water pooling up in the bottom. I made that mistake with my first build. I used materials such as common rocks in the bottom, fabric separation and planting soil on top, covered with moss. This was a bioactive draining system but poorly made and cheap. It resulted in water pooling up, mold outbreak and a terrible smell from rotting plants. It did my cham no good. My terrarium was planted all with plants that was supposed grow in conditions like that but. Well. That foul smell told me otherwise.
If you are serious about keeping a working enclosure with substrate you should make it bioactive and use materials that's able to soak up water.
The bottom cover should be a thick layer with hydrograins and a drainage possibility. I just use a cut in half bottle in the corner of my enclosure so I will be able to drain it like an aquarium if water start pooling up.
The hydrograins should be covered with a separation layer like the exo terra biodrain mesh.
The next layer could be plantation soil that is bought at pet stores. In difference to the planting soil this will not mold and as the hydrograins it will soak up water.
Substrate must always be covered. I use moss, big thick pieces, impossible for my cham to eat by mistake.
I've had no water pooling up with this build and it is very dry for a glass setup which minimize the risk for RI. My enclosure do fine with 3 mistings a day.
If you want more details on a build like this, check out my thread:
https://www.chameleonforums.com/threads/incubus-bioactive-project.145373/