I live in a suburban area and I am beginning to plan out a new area in my yard. I have a small typical suburban yard but where I live my backyard is down a hill. My family put in two retaining walls so now we have three levels my house on the top, a vegetable garden in the middle, and a chicken coop, fruittrees, and shed on the bottom. My question is about the upper most level, I want to design a perennial permacultural site in Southern California (outside San Diego), I want to use the most efficient water harvesting techniques. I have read Brad Lancaster's books about building rainwater catchment systems into the landscape. But there is one point in the book (and forgive me I don't have the book with me so I can't get you the page number) where Lancaster mentions not having swales within a certain distance of your foundation becuase you don't want the water to get under that. But is it a problem if I create a bio swale system that would harvest rainwater behind a retaining wall? The distance from my house's foundation and the retaining wall is about 20-30 feet. Does anyone have any experience with this or know any resources I should look into? Thank you so much!
You've probably already developed an answer for this but if not, here's some notes from an erosion problem I've been working on.
You can dig a swale "near" your home foundation depending on how deep it is, how the water is sloped, volume of flowing water, and what is down stream. Key objective is to move water away from the house rather than holding it. Never retain any water near foundation or behind retaining wall unless it is in a container (like a pond liner or tub.)
Start working up stream in the watershed. That might mean capturing and diverting all roof water so you decrease volume around foundation. Then use small trench sloping water away from house. This is how I solved a pooling problem around the front of my house -- don't have full rainwater catchment, but did clear the gutter so water would move away from impacted area.
Behind my house I have erosion 4 feet from the foundation in one area about 16 feet long. Below that is a 20 to 25 foot hill with retaining wall at bottom. Top of the hill I raised the soil near the foundation by 12 inches, sloped away from the house at about 10 degrees with a small trench top of hill. Back side of that trench is silt fence and tiny rock wall that I used so I could build up soil. Near house was seeded with grass, trench swale and berm with a cover crop.
Here's a picture a week or so after finishing the back. Objective was to restore hill while slowing water down before going down larger hill ...
Front design was different but a picture can't really show the slope. It's also covered with clover and wheat now.
Both required me to clear drain pipes, raise elevation near foundation, and direct water away from house. My harvesting happens further away in garden area, or small mulch pits in front of shrubbery away from house. Harvesting rainwater near your foundation is always a bad idea, but using swales to move water away from your house is smart management.