could you please jot a couple of very simple diagrams showing a plan and cross section of how this drain relates to house and the route of drainage? Does not need to be to scale. Just want to see the scheme. Also, a picture of the actual area does not hurt; it can help alert to things that may be overlooked.

Ok. Thank you. Yardvaark. I will upload some drawings/pictures once I get home from work tonight.

Until then, here are a few details of the situation in lieu of a picture: I have a collector drain already installed along the edge of the patio and I asked you for advice on that installation a while ago here on Gardenweb: http://forums2.gardenweb.com/discussions/1421449/french-drain-or-culvert-or-else

I installed a perforated pipe along the edge of the patio, which directs water to either side of the house. On the side in question (north side), the collector drain empties into a swale, which I am in the process of reinstalling. But I am concerned that some water will seep not through the pipe but through the gravel bed of the collector drain and therefore will not be captured by the swale and may drain below the swale into the soil toward the foundation of the house. The purpose of the new drain along the north slope is to capture that water and take it out away from the house.

I did a little test with a hose to see if a perforated pipe on a slope would in fact keep the water or lose it all. It seems like it will keep it up to a certain volume. I also assume that the gravel bed itself, which sits on clay will function as a drainage channel. Not very scientific, but I am leaning toward using a perforated pipe at this point, but obviously love to hear your expert advice. Thank you!

Capturing the water in a trench, you're not going to direct ALL the water into the pipe. Some will seep into the ground. But the objective is to get the bulk of the water to a place where it will not cause problems. It's not possible to keep the ground dry from all rain.

Hi Yardvaark, I created a couple of drawings that I hope will give you a better idea of the situation. The old post I referenced above also gives you a sense of the overall topography, but does not include a photo of the north side of the house, where I am planning to install the drain. It's dark now over here and taking a photo now won't help.

Anyway, the plan view drawing of the house shows in green the already installed collector drain along the edge of the patio. It carries water from the gill out along the north and south end of the house. It is working well so far. At the north side it was installed to dump into a swale, but I am redoing the swale now. As you can see in the drawing of the elevation, right at the end of the existing (green) drain, water does seep through the gravel bed and not necessarily travel through the pipe. And I am concerned that it may find its way into the soil below the swale. Therefore, I thought the installation of a drain would make sense to direct the water down the hill and intercept any water to move it away from the house and footing either in the embedded pipe or through the gravel bed. At the bottom of the hill, the water would empty into a dry riverbed that runs through our property.

I wonder now not only if this design makes sense, but also if it is appropriate to install a perforated pipe along the slope shown in the elevation? Or would it have to be perforated at the top to collect the water coming from the patio collector drain and then turn into a solid pipe to take it down the steeper section of the hill?

I would love to hear your perspective on that. Thank you!

The drawings (which are vastly better than necessary!) help a lot.

It is fairly common that drainage for collecting water is installed AT THE BASE OF A FOUNDATION WALL when a house is being built. Therefore, any groundwater adjacent to the foundation would have an escape route instead of building up and applying pressure to the wall. In the picture, you are installing the same type of drain system, but it's positioned at a higher elevation so as to catch only water near the surface of the ground, just below the concrete swale (where it's unlikely that there be much, if any, because of the shielding effect of the concrete!)

Without seeing a picture of the actual area, I'm not sure why you chose to route the swale immediately adjacent to the house. Usually, one would want to slope earth away from the wall, directing water to follow that path. Depending on how much land space there is, it would be preferable to place the swale several feet from the house. (Imagine an overflow situation. If the water is immediately adjacent to the house wall, it's making contact with it if there is overflow.) If there is a torrent of water I could see the need/desire to line the swale to some degree with concrete.

If you discover that there is no drainage at the base of your house foundation, I could see installing a collector drain system AT THE BASE (not several feet higher along the foundation wall.) If the base is already drained, I can't see the need or advantage for adding any other collector drain system above it. In that case, just sloping the earth away from the wall is sufficient. If the swale carries much water and the plant materials (grass/groundcover) are not sufficient to prevent erosion, then I can see adding concrete lining to the swale center.

Let me know if I'm "missing" something.

Thank you, Yardvaark. This is super helpful. I took some pictures of the area this morning. See below. Light was very low, but I hope it gives you a sense of the layout.

I was planning to slope the swale away from the house and create a space of about a foot between the v-/u-shaped channel and the house. I posted a drawing of cross sections of how I imagine the swale being built below, which illustrates how the swale is the deepest at the top (to be below the pipes that come from the patio collector drain) and how it becomes more shallow toward the bottom of the hill.

Our property ends 5 feet from the wall of the house, so unfortunately I can't move the swale any further away.

Our house was built in the 50s and there is no drain placed next to the foundation. I am worried about getting closer to the foundation without the consultation of a structural engineer.

My hope is that the drain will capture any water that seeps through the gravel bed from the patio drain and therefore will run below the swale while also intercepting any water that is trying to move laterally toward the foundation. I assume that the sealed surface of the concrete swale will prevent any water from entering from the surface.

Given the situation and also the fact that I already dug the trench, do you suggest any important changes to the design of the drain/swale that I need to incorporate to make the installation effective?

It's my belief that the swale/flume will be the workhorse of the system and the gravel trench/pipe will do little to nothing. The good news is that it won't harm anything! Based on your drawings and what you say, I believe you will do a good job. Have fun!

Thank you, Yardvaark. And apologies for the delayed response. My main reason for installing the drain in a gravel bed underneath the swale is that I noticed that water from the patio drain it not only traveling through the pipe but also through the gravel bed surrounding it. My fear is that it would not be captured by the swale but flow underneath it and potentially laterally toward the house footing. I hope the drain/gravel bed underneath the swale will capture that additional water and take it away. I created a quick drawing to indicate the flow of the water from the patio drain (which is collecting the water that comes from the hill behind the house). Thank you again for your help. I guess the El Niño year will show if my installation works....

I understand better what you're trying to do and why. I would have designed the head of the concrete flume such to catch whatever might escape the upper gravel bed. Couldn't really say what you're up against having water traveling through this underground channel below the concrete. Don't know how water will exit it, how much water there would be and if it will have the capability of relocating any gravel as it travels along, due to increased slope. There are quite a few unknowns here.

Ok. Thank you, Yardvaark. How would you have designed the head of the concrete flume to catch the water? Simply start at a lower elevation than the upper gravel bed? Or do something completely different? Thank you.

Yes, start at a lower elevation. It's a bit of an unusual situation as the drain is not continuous, so it would require some creativity. You must retain the upper level gravel surround yet let the water continue. I'm thinking something along the lines of a headwall with a lot of weep-hole action, caught be a lower elevation flume. The small size gravel would need to be retained (filtered) by larger rocks before coming to the headwall. The pipe extends through the headwall and is caught by the flume. I think doing something at the headwall would be easier than creating the drainage trench and system. Still need the surface flume, though.

Thank you, Yardvaark. That sounds like a good plan. I already put in the drain pipe along the slope over the weekend, so that's already there and can't be reversed anymore. But I guess it would be doing any damage, judging by one of your earlier comments.

I was also thinking about putting a lot of weep holes into the headwall, but I am not sure how to construct them. Are they just vertical slots? Are there pre-fab pieces that can be inserted into the wall, or do they need to be formed? Can you direct me to a website or drawing of how that should be done?

You mentioned large rock in your last comment. I used 3/4" crushed rock for the gravel bed. I didn't know that there is larger gravel than that. What is the size of that rock?

Thank you again for your tremendous help.

I'm thinking that you would strain water from the gravel via weep holes. But if the gravel is only 3/4", the weep holes would need to be slightly smaller than that in order that the gravel does not pass through as well. Too small and they are too easily clogged or limit the amount of water passing through. Therefore, a section of larger rock (3") could be used to used to retain the smaller gravel and the larger rock would not pass through the holes. Vertical slots would be the preferred hole in order to retain rock but allow the maximum amount of water to pass through. I think you would need to fabricate such a thing because your situation is one of a kind. I can't direct you to a website or drawing. I would just think this through and draw out the pieces in cross-section and elevation and if you do that, I think you will understand how to fit it together.

Ok. Thank you, Yardvaark. I discussed this with the contractor who is pouring the concrete and at first he looked at me a little perplexed but then suggested to use foam inserts (such as pieces of foam strips used to isolate concrete from other structures) to create the vertical slots.

In order to hold back the gravel or larger rock, I probably have to install some kind of wire mesh. I assume it won't matter if it's going to rust since it won't have a function anymore once the headwall is in place, correct?

the wire mesh would be temporary, I presume. Wouldn't matter if rusted away so long as the gravel being held is larger than the holes in the headwall that are holding it.