In the photo below you will see the direction that water naturally drains off our patio based on the slope. The water actually ends up in the corner to the right not shown in this photo but this is for illustrative purposes.
A small hole is bored out in this old concrete block wall which allows the water to spill out of the wall and into an antiquated drain. We intend to replace this drain as it has been backing up recently.
The question I have is what is the best method for collection just as the water exits? We will be using 4" PVC as conduit. The first option I have looked at is a simple grate cap that fits into the 90 degree angle piece. We would set this end of the pipe in concrete to give it the right elevation change.
Another option we have considered is installing a larger catch basin here so that we can have a larger grate. One concern I have is that allowing the water to leech out this close to the home would be an issue. Is that valid?
The biggest obstacle in this project is that our lot is nearly flat from front to back. We will be draining to a roadside ditch made of earth. We need to run the conduit a span of ~40' and only have about 3-4 inches to play with.
I have considered taking the line as far as possible and installing a 90 degree at the exit point with a spillway cap. Are these prone to backing up? It seems to me that the system depends largely on water building up in the pipe in order to spill out. That concept makes me somewhat nervous.
If we drop 1/8" every 10 feet for a 40 foot span would that suffice? This drain will only service ground water and patio runoff - all of our gutters are equipped with downspout drains.
Thanks so much! Water is my vice and it's great to have you guys here to bounce ideas and thoughts off of!