14
Had a retaining wall collapse after one big rain last month
Expanded clay blocks looked solid but the base shifted after that 5 inch storm in one night. Ended up having to dig out the whole thing and install a proper french drain behind it. How do you calculate drainage needs for a sloped yard?
3 comments
Log in to join the discussion
Log In3 Comments
parkerbrown27d ago
You ever look at a pile of wet clay and think "yeah, that's basically a brick that used to be dirt"... because I've been there. That 1% grade tip is the real deal though, I learned the hard way after my first french drain just turned into a mud spa for the local raccoons. For what it's worth, I ended up digging a trench almost 3 feet deep in my yard because the clay here is so bad it's practically waterproof when it's wet... basically had to give the water a whole subway tunnel to escape through.
8
skyler_jackson2728d ago
i was actually reading about this the other day on a landscaping forum, someone said the rule of thumb is like 1 inch of drainage per 10 feet of slope for a 1000 sq ft area, but that depends on your soil type. if you've got heavy clay like me, you basically gotta assume it's going to act like concrete when it's wet and plan for way bigger pipes. the guy who replied said he used solid 4 inch perforated pipe with a sock around it and a 2 foot deep gravel trench, and that handled a similar 5 inch storm no problem. also they mentioned angling the drain pipe at a 1% grade minimum so water actually moves instead of sitting there.
6
williams.sage27d ago
Honestly, I used to think you could just throw in a french drain with some basic gravel and call it a day. My yard flooded after a 3 inch rain last spring and I figured a shallow trench would fix it. But reading about that 2 foot deep gravel trench with the sock around the pipe really clicked for me. I've got clay soil too and that "acts like concrete" line hit home. Now I'm thinking I need to dig way deeper than I planned and go with that 4 inch setup for sure. The 1% grade tip is gold too, my old setup was basically a puddle maker.
3