I haven't added plants yet because....

During a heavy rain, the terraces puddled up badly, becoming swampy, and even after three days the soil is still very wet and muddy. I don't understand why the drains aren't carrying the water away.

I'm planning to build up the topsoil with mulch and manure. Will that help? Any other suggestions?

(I accidentally posted this in the gallery. Can I delete the gallery post?)

What you should have done was to have pitched the terraces slightly so that the water landing on them could runoff. This is usually done toward the wall on the lower side. Each wall should have gravel all theway up to the top of it right behind in that goes all the way to the bottom where a perforated pipe that is pitched to carry away the water should be.

Gravel open to the surface accepts the runoff and gravity lets it work its way down to the bottom of the gravel until it meets the subgrade (soil under the gravel). Then it begins to fill up the gravel with water from the bottom up until it gets to the height of the holes in the pervious pipe. Then it enters the holes and starts flowing down the channel between the two rows of holes in the PVC piping until it comes out the other end or until it reaches a dry area in the gravel surrounding the pipe if there is more water in the pipe than the channel between the rows of holes can hold. Then it leaks out of the holes which is perfectly OK.

If the gravel behind the wall is not open to the suface for water to enter, it will only get the water that the soil is ready to give up. It won't give it up until it is saturated. Water only moves through soil by gravity once it is saturated. That means that if you isolate a soil over gravel, it will keep it until it gets completely saturated or until it dries out from the surface.

In other words, subsoil drainage does nothing until the soil is saturated and does nothing to prevent it from becoming saturated.

We sure have discovered that the drain should have been covered with a permeable liner and the layer of gravel should have been covered with sand.

We DID line the interior of the landscape tie walls with a 20 mil (?) liner used for ponds, etc. as recommended by the garden supply center we use. Not sure why they didn't give us more info about the correct install of the drain - maybe I wasn't clear, or maybe, since I was buying that from Home Depot they figured I'd get more detailed advice there. Shame on me.

We've been told that most of the problem can be alleviated by placing a "gravel well pit" 5 ft deep below each middle terrace drain pipe that drains into the bottom terrace, which should allow the bottom terrace to recover more quickly withou having the middle terrace water added to its saturation. Plus we have added mulch and manure, so we'll see how it drains after the next storm.