I live in Southern California, it barely rains here. However, I am working on my yard and just built a retaining wall and was required to use perforated 4" pvc pipe behind it.. Now I need to do the other part of my yard and Im wondering what's the best solution for the drainage. Can I just just use the solid pvc? HOA is requiring me to install drainage, but no requirements as to what material to use. Anybody has an advice to what's the best solution would be? 4" solid pipe? it will drain to the front yard where we are required to have pea gravel for that reason. And if solid PVC is the right material, do we need the gravel on the trench at all? Thank you.
I'll show you the two things that are recommended where I live in upstate New York (but we get occasional torrential rains here):
It's called perforated pipe. First, here is the kind, black, that can be bent into a gentle curve:
Hopefully you can see the slits that allow water to go through. It comes in 6 inch or 8 inch diameter. For residential projects, people generally use the 6 inch. You can buy it at Lowes or Home Depot, in 50 or 100 foot rolls, or in ten-foot lengths which you can join with connectors.
Here is the other type, white, rigid, with small round holes. If you need to turn a corner with this system, you need special connectors.
This kind is a bit more expensive, but it's very good for areas where you're having trouble achieving a 3% drop (in absolute height), because in such areas it's hard to shape the bottom of the trench extremely precisely.
I like to use two-inch river rock (no sharp edges) instead of pea gravel, as the larger the rock, the greater the total pore space. Clayey soil and pea gravel, over the years, can cement themselves together quite effectively. Here's what the river rock looks like (the label will say 1 to 2 1/2 inch diameter):
Aesthetically, I like the appearance and texture much better than pea gravel.
You can have a truckload delivered or you can buy a bunch of reasonably-sized bags at a big box DIY store. If you have a truck, bulk makes sense because you won't have to pay the delivery fee.
You can buy a sock material, but I think landscape cloth gives better protection.
The project will have less encroachment of weeds if you dig all the weeds out completely before you begin, and if you weed the finished project regularly. But there will probably be sections, away from the house, where you'll want to lay the removed sod back on top when everything else is complete. I do use landscape cloth, but test it first to make sure that water can drain through it.
There are different schools of thought about where to put the landscape cloth, and I'll let you read about them on your own. For example you can simulate a sock by wrapping a long rectangle around the pipe lengthwise.
As you are leading the water away from the building, you'll want the pipes to point somewhat downward, at least slightly. The ideal is at least a 3% grade, but less is possible in a pinch.
Note that in some sites you don't really need all this gadgetry. You can just shape the landscape to make gentle downward-pointing swales that take the water where you want it to go, as surface runoff water.
The raison d'être of all this work is to lead water away from the foundations of the house, or in your case, from the retaining wall. The easiest way to deal with the water is to deliver it to the street with a pipe that goes under the sidewalk.
The idea behind perforated pipe is that it will allow some water to filter out through the openings and drain into the ground, and it will also carry water from Point A to Point B. So, a combination approach. Another reason to perforate the pipes is to enable them to capture water along the pipe's length.
It sounds like your ordinance may have been written many years ago when the microclimate in your area was less dry than it is now. Or it was lifted whole, with no editing, from a different region.
I hope you can enjoy the silver lining of the aridity where you live, that protects you from torrential rains.