Any time any kind of construction is mentioned on this blog, drainage is always the second talking point. That’s because when it comes to construction, water is the enemy. Overly saturated soil can blow out retaining walls, improperly installed drainage pipes can cause sink holes, and uncontrolled runoff can flood a basement or erode the surrounding landscape.
If any structure is expected to last more than a year or two, any water that may come into contact with it has to be accounted for.
Run off is the first danger. Run off is any water that isn’t immediately soaked into the ground. Water that lands on roof tops, driveways, and other flat surfaces almost always turns into runoff if not controlled.
Gutters, drainage ditches, downspouts, french drains, dry creek beds, etc. are the first line of defense against runoff. They direct the water away from buildings and such to an area that can absorb the water safely.
Erosion is also a huge problem caused by run off. If too much soil is washed away, it can destabilize a hill side or block up a stream .
So from the things listed above, water needs to go into pipes directed away from the house
Corrugated pipe is usually the default for drainage. It is inexpensive, light weight, and flexible. And while this makes corrugated pipe easy to work with, it also makes it prone to breakage. If hit by a shovel it’ll break, if buried under a road way it can collapse etc.; corrugated pipe just isn’t made to last.
Slick drainage pipe is just a giant PVC pipe. While they are more expensive and take longer to install, slick pipe is much more durable than corrugated and is designed to withstand the test of time. They also don’t have the ridges that catch dirt and debris like corrugated pipe so they are less likely to get clogged.
Even water that’s already been absorbed into the ground can still cause damage. When saturated, dirt (especially red clay) gets heavier and it takes a while for the water to filter down thru the earth. This static water pressure is a danger to structures that are up against dirt: aka basement walls and retaining walls. If the water sits up against the wall with out anywhere to go, best case the wall leaks, worst case the wall could blow out and collapse under the weight. Putting gravel between the dirt and the wall helps water drain away faster and putting a drainage pipe at the bottom lets the water drain safely away.
The final take away, water flows down hill and will gladly take out that brand new retaining wall if you don’t have any drainage.