Swale Depth / Width and Berm Height?

Built an A frame level and marked a contour line. I'm digging into a slope what kind of angle should I try for on the uphill side? 45? Downhill side? same? How deep should I make it? I'm eventually planning to fill the ditch with free mulch from the county. I really need to plant some apple trees I bought on discount. Five fifty a tree. i know they should be planted in the spring or fall, but I can afford to loose some of them at that price.

Spillway? I'm thinking of putting the spillway level with the natural ground on the downhill side. Should I let it come above that a couple inches to more effectively charge the berm? Half the height of the mound above ground height? Opinions? Advice? I'll be catching water from my house. Three quarters of the water from the house will enter the Swale. The roof pitch a little sever. I wouldn't want to walk it. 10-12?

Hi Anthony, welcome to permies.com, or at least to posting!

Lots of good info in your post, but a couple more pieces that would help are your location, and some info about how much rainfall you get. If you have an idea of the catchment area that would be great too.

In the sat pic, which property are you?

From there you can figure out if the spillway will be needing to handle a lot of water frequently, or if it is more for the rare exception... not much point to increase the swale capacity if it is unlikely to ever fill that high!


As far as the angles go, I would obviously worry more about the angle on the downhill side. If the uphill slide is too steep and erodes into your swale... meh, no big deal on this scale. You could then widen the swale a bit, or just dig out what fell in until you hit upon an optimal slope. OTOH, if the bottom side goes downhill, that's at the very least more of a nuisance, and possibly an outright problem. I'll take a look at my Lawton DVDs and see if I can spot a rule of thumb for this downhill angle.

Thanks for the reply Dillon!!!

North of Atlanta Georgia, US. Rainfall is 48.61 inches a year. I see 3.7 inches per hour listed as a max based on a 100 year period.
As far as a catchment area water that leaves my property goes downhill to a wetlands area and a creek. No danger in flooding.
I'm digging the swale to slow the water and charge the hill behind my house with water.
The soil has a lot of clay in it. Drainage is not very good. The hillside is compacted and rain usually just runs off.
The compaction keeps the soil from washing away but grass doesn't like to grow in it.
I'm planning on amending the soil in the berm with mushroom compost and planting the berm with white and red clover.

Upload a picture with the property highlighted.

I believe the swale will be about 80ft. I need to calculate the surface area of the the back yard above the swale and the run off from the house to determine the depth I would need to harvest water optimally.
Average rainfall per hour/ soil drainage per hour. I guess I shouldn't obsess about the details other than my berm height is consistent (always well above my spillway), the bottom of the swale is level, and the most important my spillway is level and well below the lowest berm height. I can always watch and remove dirt from the swale bottom to increase water capacity. I just won't want to touch the berms after the cover crop takes.

Thanks!

Dillon based on your advice on the backside angle I'm going to extend the mound to a tree pile I made a few months ago on two of my trees. I had twelve pine trees cutting off all my southern sun. I cut them down delimbed them broke up the branches and put a few of them in a pile braced against the trunk stumps I left standing. I'm also intending on sending my overflow into this tree pile. The extra dirt from digging the swale between the first two trees in the picture will go toward connecting the mound to the tree pile behind and widening around the trees.

The last of the five trees went in the ground after work today. The slope on the back side of this to be berm is very steep. I opted to put in four posts made from trees I'd cut down this weekend. The posts are in the ground about two feet. They will rot eventually but by then I will have time to put in a gabion wall(least expensive retaining wall option I've read about. Anyone have any other ideas?) behind it. Now to connect the ditches, increase the size of the mounds (decrease the downhill side angle), and add a bit of straw and plant red and white clover. I've been debating adding a few pieces of flat cement block along the sill of my spillway and in front of all the trees on the ditch side. I planted them closer than I should have and need to build a good ring around the tree for watering.

Hi Anthony,

Wow, those trees are a lot bigger than I expected for that price, no wonder you had to grab them! Looking good, I think you're on the right track.

I didn't have any luck with the Lawton DVDs, it takes forever to navigate on a TV and the DVD drive in this rig is apparently toast.

Anthony Alford wrote: I guess I shouldn't obsess about the details other than my berm height is consistent (always well above my spillway), the bottom of the swale is level, and the most important my spillway is level and well below the lowest berm height. I can always watch and remove dirt from the swale bottom to increase water capacity. I just won't want to touch the berms after the cover crop takes.

Exactly. No need for the top of the berm to be real precise, as long as the bottom and the spillway are good. I like the idea of cement blocks for spillway if you happen to have them.

The more settled and heavily vegetated your swale mound is, the more slope you should be able to get away with... I would be disinclined to put in 80ft of gabions if not absolutely necessary. I think your log restraints are great as a temporary solution while everything gets vegetated, and I'd be hoping that by the time the logs are shot, the decay of the wood will have brought the slope nicely in tune with the natural hill slope. If the hill was maintaining that shape well before you came along, it should be able to do so again once it has settled and been reinforced by roots, right?

The vertical posts holding the mass of wood might be the weak point; if those look to be starting to give out before the rest has rotted/settled/been colonized by roots sufficiently, maybe some rebar would be advisable...

Maybe a vine of some sort would be a good fit on the steep far edge of the swale? It's horrible stuff, but the invasive english ivy which is established on a very steep scree here seems to work wonderfully to keep it stable.

It was a great deal on the trees! Of course it inspired all the digging. I wanted them in the ground so I wouldn't have to water them everyday. I'm trying to water them every other day for awhile. It is very hot here 90+. The trees are gangly and a few where root bound pretty bad. The one on the end may have a blight or something. Pictures of swale progress and the not happy tree. I'm not sure if I should cut the branch off, let it do what it's going to do, or remove the whole tree.

So much to do i'm not even thinking about when the tree posts rot yet

The branch will be dead soon i'm sure. I may still be able to get another $5.50 tree to replace it.

Just for anyone looking at this in the future:

The general engineering rule of thumb for non-stabilized slopes is 3H to 1V.  Typically the range is 2:1-4:1 depending on your soil type with clay like soils able to hold up a bit more. Note that these numbers assume that the slope is compacted as well which is not the typical case with a swale. Once your swale is totally vegetated, it will be much less prone to eroding and a steeper slope may be permissible. With that said, it is wise to consider the worse case scenario where a large rain event occurs before your swale gets constructed.