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#63691 - 01/21/06 03:39 PM Key hole
Keith Price Offline
Lunker

Registered: 12/31/05
Posts: 74
Loc: Evangeline, LA
Ok...dumb question...what is a keyhole and do you need one in a .5 acre excavated pond?

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#63692 - 01/21/06 06:43 PM Re: Key hole
Russ Offline
Lunker

Registered: 04/18/02
Posts: 1011
Loc: Ulster Park, NY
Keith,

If the "keyhole" you are talking about comes from this post

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=20;t=002335

I think its in reference to an earthfill dam. During the construction of an earthfill dam, an essential element is a keyway or core trench. The keyway/core trench is an excavated trench cut through the center of the dam. This trench is then filled with an impervious, compacted material(clay) that prevents seepage. Seepage affects the integrity of the dam and may lead to catastrophic dam failure.

An illustration of a core trench, with an explanation, can be found on pages 37, 39, 44 and 45 of USDA AG Handbook 590. I cannot get a link to the handbook but doing a search should get you there.

And to finally answer your second question, an excavated pond is basically a hole in the ground to catch water and, in most cases, does not incorporate a keyway/core trench.

Hope this helps.

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#63693 - 01/21/06 10:40 PM Re: Key hole
Bob Lusk Offline
Editor, Pond Boss Magazine
Lunker

Registered: 04/10/02
Posts: 3100
Loc: Whitesboro, Texas
Russ is right on with his answer. A keyway is an underground waterproof barrier, necessary in porous soil areas. The keyway/keyhole/core trench is not only necessary to manage leaky soils, it also can serve as a foundation on which to build the dam. Rarely do excavated ponds have a keyway...unless layered soils are permeable. I have seen one excavated pond in 26 years which needed a keyway...all the way around it.
_________________________
Teach a man to grow fish...
He can teach to catch fish...

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#63694 - 01/21/06 11:33 PM Re: Key hole
Dave Davidson1 Offline
Moderator
Lunker

Registered: 01/04/06
Posts: 13486
Loc: Hurst & Bowie, Texas
To add to what Bob says, all soil is porous. Just ask Mike Otto.
_________________________
It's not about the fish. It's about the pond. Take care of the pond and the fish will be fine. PB subscriber since before it was in color.

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#63695 - 01/22/06 08:04 AM Re: Key hole
Brettski Offline
Ambassador
Field Correspondent
Lunker

Registered: 10/07/05
Posts: 6886
Loc: Illinois
I met and enjoyed a few good learning sessions with a CD agent in an NRCS office in north-west Illinois. I came back to him a couple of times later as I inspected properties for pond-ability, even tho they weren't even in his county. At one time, during a Q&A discussion, we talked about the wisdom of cutting a core (aka; keyway/keyhole), and he related a short story about a local farmer that used his own bulldozer to build his pond. He dismissed use of a core. Shortly after it filled, the entire dam mass started to move from the water pressure. Another man-made disaster.
_________________________


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#63696 - 01/25/06 06:33 PM Re: Key hole
Trent Lewis Offline
Lunker

Registered: 02/03/03
Posts: 95
Loc: Prosper, Texas
Keyways or core trenches are necessary in most ponds we design and construct no matter what the soil type. The more water (or hydrostatic pressure) the more need for a keyway.

Make note of the main reason for a keyway:

***Original grade soils and embankment (or dam) soils must be "tied" together. This also is in relationship to the "compaction factor". A keyway makes this "knot".***

If keyways are not used, water finds the area between the original grade and embankment and scoots out where the path is the least resistant.

Brettski illustrates this principal well in his antidote.

Hope this helps!

Trent

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#63697 - 01/26/06 07:35 AM Re: Key hole
Keith Price Offline
Lunker

Registered: 12/31/05
Posts: 74
Loc: Evangeline, LA
Trent Lewis

I can understand having a keyhole/keyway for a pond with a dam but don't see the need for one in an excavated pond. Am I missing something here?

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#63698 - 01/26/06 07:51 AM Re: Key hole
Brettski Offline
Ambassador
Field Correspondent
Lunker

Registered: 10/07/05
Posts: 6886
Loc: Illinois
Keith,
Naaa, you are on the right track. The thread kinda veered a little bit with the mention of a keyhole. An excavated pond is nothing more than that...a hole dug into the ground. The keyhole/keyway/core comes into play for an embankment pond where a dam has to be created to block up the end/edge of a pondsite to capture the water.
_________________________


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#63699 - 01/26/06 08:20 AM Re: Key hole
Keith Price Offline
Lunker

Registered: 12/31/05
Posts: 74
Loc: Evangeline, LA
Thanks Brettski!!!

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#63700 - 01/26/06 08:30 AM Re: Key hole
Trent Lewis Offline
Lunker

Registered: 02/03/03
Posts: 95
Loc: Prosper, Texas
Right on, Brettski!

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