I live in the outer Richmond district of San Francisco, so the soil is more like sand than dirt. We've terraced our back yard with two ~3' retaining walls. We are putting in two paver patio's, but I'm not sure how to handle the runoff from the patio surface.
Is a drainage system needed in such sandy soil?
Soil drains very well, but concerned about the runoff accumulating behind the retaining wall.
As far as I can tell there is no existing drainage, so even if I put in a drainage system to handle the runoff where would it drain to? No drainage going to the street or anything like.
If the soil is sandy then runoff will not accumulate anywhere. The runoff will simply soak into the ground and go down, down, down as far as the sandiness goes.
Use sand between the paver blocks so the surface of the patio can count as drainage area.
Stick to your lawn watering schedule until it really starts to pour. After the storm you have only the same number of rest days you always had and then you need to start watering again.