Pond Boss Forums POND CONSTRUCTION Building a dam How steep of grade can dam be?

Hello. Knock on wood, I'll be building a pond later this summer. I'd like it to be bigger but I think my site will only top out at about 3/4 of an acre. The back of our pond dam is in a spot that I won't be mowing, so I can have it as steep as possible, with my thinking that I'd rather go as steep as possible to have a little more water (granted probably only a little bit more). So, can any of you builders tell me how steep I can go just from a dam soundness standpoint?

Hersh

How tall will the dam be?
Your pond will be here longer that your house build it strong.

The book says 3/1 for ever 1 foot it goes up you go out 3.

2/1 back slopes are not uncommon with the right material.

Looking at a lot of old dams there are a lot of back slopes that are almost vertical, It will depend on the material and how high.

OTTO

Hey Hersh...welcome to da pond show, man.
Otto is the Dirt King around these parts. Listen to him and heed his advice.
The only other thing I might bring to the table is this link to the USDA Publication #590 for pond construction. The details of the specific construction spec's that you seek begin on page 56. The entire publication is an excellent basis of information, but very little can beat the experience of guys like Otto and ground truth. To get both of these facets combined, seriously consider picking up a copy of the latest/greatest compilation of literary expertise in pond construction; Perfect Pond...Want One?

Thanks Otto and Brettski for the info. Otto, I'm estimating the dam will be about 20' high.

Hersh
At 20 feet,you better soften the back sloop and not have it to worry about.
OTTO

Hersh
At 20 feet,you better soften the back sloop and not have it to worry about.
OTTO

Sorry for the late post. I've been away from the site for awhile.

I have a 40 year old dam. The dam face is too steep. It's about 24-26 degrees. It holds water well, but is difficult to maintain. I have to weed wack it by hand. I've tried two types of mowers, but nothing will stay on the surface.

You say you won't have to mow, but you do have to mow or trim occasionally to keep woody plants from growing. So, try to get a 2:1 slope at a minimum, 3:1 is much better.

dave

hersh,

The angle of repose for pond soils is about a one and one-half to one slope. Years ago here in Texas most pond dams were build like this... with free-fall dirt for the back slope. In more recent times (about the last thirty years or so), our SCS Field Office policy was to stake nothing steeper than 3:1 slopes on farm ponds. This was to facilitate establishment and maintenance of grass cover on the exposed slopes to reduce soil erosion.

Those older dams with the free-fall back slopes have remained surprisingly stable over time, in my view, probably because of their relatively high clay content which is somewhat less erosive than the coarser-textured soils not typically associated with good pond sites.

Rick

On a twenty foot high dam you will gain about 30 feet for water storage by having a free-fall back slope rather than a 3:1 back slope. Good luck on what ever you decide.

Hersh
Good to have you back we wondered where you went.
There have been lots of dams with the free fall back slope that Rick talked about, they will work, but I will not allow anyone to have one without a little fight, You will probably be ok and the extra 30 feet of water is a lot.

Otto