Trench Width and depth?

I've got a level terrace that is approx. 17 feet wide by 100 plus feet long, with an east-west orientation. I am going to put a hugelkulture bed down the middle of the terrace. I am going to do this in stages , approx. 40 to 50 feet to start, so that I can get the wood into the trench without carrying it too far, and to see how it works out before proceeding further. Either every 30 feet or 50 feet I am going to have a break in the bed to allow for excess water movement from the uphill (north) side of the terrace and for access to the other side of the bed.

On one side (north) I am going to plant fruit trees, on the other (south side) I am going to plant vines (grapes, berries, etc.), on the bed itself I am going to plant annual veggies and flowers.  The trees and vines are going to be as far as I can get them from the H. bed, to keep shading of the bed down and to allow a walkway between the bed and the trees/vines for weeding, pruning, harvest, etc.

My main objective is to test the H. bed as a means of water storage for the bed, vines & trees, as we have very hot dry summers here (SW Oregon), and water is at a premium. In, but near the top of the bed I am going to use soaker hoses to distribute water the length of the bed. I have one 1,200 gallon tank and am going to set up another larger tank, that I use for rainwater and greywater storage. I am going to have the excess water during the rainy season overflow go to the soaker hose/bed. I am using forest litter, wood chips, leaves, etc, in my present (small) orchard, and will do the same on this terrace as a means of retaining water in the soil.

My main question is; How Deep and How Wide should I make the bed? I'll have my local backhoe operator dig the trench.  I am thinking 3 feet deep and approx. 3 1/2 to 4 feet wide.

Your thoughts, criticisms, and ideas are appreciated.

Thank You,

Jerry

I don’t know if I was right but I did mine about 4 deep and 7-8 wide. I never measured the width. Just getting a sprout or two coming up now

I am not an expert.  I would say your on the money.  As far as width you want to be able to reach the center so you can plant, harvest, and weed. Depth is entirely up to you.  Some people put logs on the ground and build up.  I'm short so I dug down three feet so I could have the recommended seven feet, and still reach the top which is about four feet high.  
I live in Northern California, we don't get much rain any time of the year, and nothing in the summer.  2020 was my hugelkultur's first summer, so I still had to water it, but only about a quarter as much as my other gardens.  I also have a couple of olla's  on top to help.  (Olla is a clay pot that is planted in the soil with only the top out. The plant roots can use the water that seeps through the pot.) I was very happy and feel it's worth the hard work to put it in.
This is a great place to be if you want to learn about hugelkultur.  Explore some of the post, and you will find a ton of information.  Good luck to you.

I think that your size aim is about right. Can I ask why you are choosing to sink it into the ground rather than build it up?

S Lowe,

I am using a trench because I need the dirt from it to build up my pile. Also, I do not want it so high that it sluff's or washes down and encroaches upon what I am doing adjacent to it.


Jen,

Thanks for the link, I will take a look at it. Appreciate hearing your results. Hope to hear how it goes this season. Your results regarding water usage are encouraging.

Thanks,

Jerry