Pond Boss Forums INTRO Questions & Observations How does a sandy pond seal itself?

Everyone around me has sandy ponds that hold water. Think there are 6 within a quarter of mile radius. My sandy little 0.2 acre hole was dug over a year ago. The closest pond, lower center of photo, is about 0.5 acre and was dug 3 years ago. It rose, then dropped, and recently filled to the top for the 2nd time this June. The dozer guy that dug my pond, also dug the neighbor's, said my soil was just the same and that it would take 2-3 yrs to seal itself. Sure enough, the other pond remains near full now, in spite of a relatively dry and hot summer. What makes these sandy ponds seal over a period of years?

luck?

how much did you pay? sounds like the guy knows.

which one is yours next door or 2 up?

Perhaps you have a more impervious layer under the sand and you have to wait for the sand to saturate above that. I find it doubtful sand itself will seal.

Sand is the leaky stuff that aquifers are made of. Water slides through it until it hits something solid. If there are a lot of sandy ponds holding water, they have something under them that stops the seepage.

Dave,

Don't you mean "pervious?"

Nah, that was the G-Man who caught Dillinger. Melvin Pervious.

Before this thread closes with amusing, yet less scientific remarks, a few notes: The soil has a low low clay content, yet does have some clay. There's your silty sand, sandy silt, and sandy silt clay Hartsell soil. The pond builder, uses alot of dozer hours mixing the subsurface layers with the deeper layers and packing it in in 4" lifts. The rock base starts off as soft sandy rock some 7' deep. The neighbors' .5ac pond took years to hold water. My dad says, (old school farmer type ) that natural growth and accumulation sometimes seals porous pond bottoms. You can see the lower .5 ac pond has aquatic growth and is darker. It was $2,050 to excavate (it has been recently enlarged slightly from the picture). The forest in draw just above it is holds a towering hardwood forest stand, has 16" of top soil and is rocky. To have the pond excavated there, I believe the price would of been 5 or 10,000 more and would have wiped out our tallest tree stand on the property. To I.D. the little .2 pond, look left of center, looks as brightly colored sand, yet if you examine the photo, there's 18" of standing water (and 7 bullfrogs). A couple of trees partially hide the south edge of it as well. Can rooted vegetation help seal a pond bottom?

Is there any possibility that the ponds are directly affected by the underlying ground water table? The water level of sandy soil ponds often are.
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Just trying to eliminate variables.

Your pond sounds a lot like ours. We have sandy clay and sandy silt, I do think that some organic build up helps to fill in the areas between sand grains, but it takes a while. Mine used to fluctuate quite a bit, but it seems to be stabilizing.

I recently found that mine is holding water based mostly on springs fed by the water table. The Hydrologist who came out said I don't have enough watershed to fill it to where it was designed. He recommended either being happy with what I have, or consider a well.

Here is the stuff from prior threads - its called sorting.

http://www.pondboss.com/forums/ubbthread...true#Post125536



http://www.pondboss.com/forums/ubbthread...=true#Post78440

We need to get George and DIED in on this as they can explain permeability and porosity of soils and rocks.

Porosity is indirectly related to hydraulic conductivity; for two similar sandy aquifers, the one with a higher porosity will typically have a higher hydraulic conductivity (more open area for the flow of water), but there are many complications to this relationship. Clays, which typically have very low hydraulic conductivity also have very high porosities (due to the structured nature of clay minerals), which means clays can hold a large volume of water per volume of bulk material, but they do not release water very quickly.

Sorting and porosity

Effects of sorting on alluvial porosity
Well sorted (grains of approximately all one size) materials have higher porosity than similarly sized poorly sorted materials (where smaller particles fill the gaps between larger particles). The graphic illustrates how some smaller grains can effectively fill the pores (where all water flow takes place), drastically reducing porosity and hydraulic conductivity, while only being a small fraction of the total volume of the material.


In the earth sciences, permeability (commonly symbolized as κ, or k) is a measure of the ability of a material (typically, a rock or unconsolidated material) to transmit fluids. It is of great importance in determining the flow characteristics of hydrocarbons in oil and gas reservoirs, and of groundwater in aquifers.

The intrinsic permeability of any porous material is:

κI = C X d2

where

κI is the intrinsic permeability [L2]
C is a dimensionless constant that is related to the configuration of the flow-paths
d is the average, or effective pore diameter [L]


] Yes many rocks(not talking about gravel or broken or fractured ones but solid rock layers) can have fluids run through them under pressure. Also clay when dry absorbs water and expands until water will no longer be absorbed and it creates a seal subject to pressure. Porosity is the space between grains of soil or rock and fluid will flow through them limited by force needed to get the fluid through the pore space.

Now George or DIED can fix what I poorly explained.

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DIED

thanks for calling out for the geo's ewest, but you did a fine job. an unintuitive physical property of clays is their high porosity and capacity to store water...well put....yet at the same time, their extremely low permeability limits the movement of that water....hydraulic conductivity (K) is basically the rate or speed at which water (or any fluid) can move through a particular media. Bill is correct in that all soils leak, its just a matter of how fast.

I apologize if I offend anyone with the following simple science, but it helps me to put things in terms that even my mosquito fish can understand. ewest hit all the important points about stuff moving through other stuff....in relation to permeability, porosity, conductivity, tortuosity (the flow paths), but for me all other things being equal, and envisioning leaky ponds i think primarily about how fast the water moves through whatever type of soil. So here are some example ranges of K (hydraulic conductivity) for different soil types just for comparisons sake......K is also given in metric units (i.e. cm/s or m/s) but my mind still thinks in inches and feet so I use gallons per day per square foot………..

Gravel : 10E4 to 10E6 gallons/day/ft2 (10E4 is scientific notation for 10 to the 4th power which is 10x10x10x10 = 10,000 - which means between 10,000 to over 1,000,000 gallons of water can pass through a square foot of gravel in one day!!)

Silty Sand to Clean Sand : 1 - 10E3 gal/day/ft2 (10E3 = 1000 gallons = gushing pond leakage)

Silts : 10E-2 to 1 gal/day/ft2 (which means 0.01 to 1 gallon of water can pass through a square foot of pure silt in one day, if multiplied by square footage of pond = very leaky pond…..you can see where we’re headed for clay….)

Clay : 10E-4 to10E-6 gal/day/ft2 (which means 0.0001 to 0.000001 gallons of water through the square foot of clay which equates to a leaky pond only on geologic time, this is a good tight pond seal).

this thread is a classic for leaky ponds containing many great insights, speculations, and statements above (theo, bill, brettski, eddie, ML...all yous guys), but IMHO to really help DonB we need to hear back from him about his construction techniques to help determine whether its just absorption into new pond lining or an actual seep. Hope the explanation on conductivity helps a few of you lurking get a feeling for why clay works so good.

My personal situation prior to renovation was hydraulic driven seepage through bedrock on pond side of dam, with water daylighting in creek below dam. In brief, this was mostly remedied by a lot of digging, cleaning, grooming and installing a well compacted mixed native and imported clay liner within deepest areas of pond subject to the greatest hydraulic pressure.
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I think you have described sorting. Different types of dirt have different grain sizes. When they are mixed and wet they exhibit sorting. I should have taken time to post the pic with the first post.

Well sorted (grains of approximately all one size) materials have higher porosity than similarly sized poorly sorted materials (where smaller particles fill the gaps between larger particles). The graphic illustrates how some smaller grains can effectively fill the pores (where all water flow takes place), drastically reducing porosity and hydraulic conductivity, while only being a small fraction of the total volume of the material.






http://en.wikipedia.org/wiki/Porosity


When dry clay is mixed with other dirt the aggregate has grains of different sizes. Water flows through the pore spaces between the grains not the dirt. When the mixture gets wet the grain size of the clay increases (swells as it absorbs water)reducing the pore space volume and the smaller other dirt grains sort to clog the remaining pore spaces to form a seal. Compaction helps because it binds the grains and reduces the pore spaces.

The water in a new/renovated pond may look like it is leaking for a while as its clay/soil mix absorbs water reducing pore space and goes through sorting and sealing. Once that process finishes it should be sealed and not lose water except through evaporation (unless there is a real leak ).

You guys are out of my league...you're just trying to get me in trouble...

No way, george. You practically founded the league.


Well, yeah, that's always one of the goals.

If your pond is above the water table, I think that's true.

If the water table never reaches your pond, eventually the sand will be clogged with organic matter, silt, and finally clay to seal the deal.

If the water table rises and falls and reaches your pond water, it will be back-flushed, and may never completely seal.

I just love the technical stuff. Thinking about it, Brettski, we haven't had a normal month's rainfall in 31 months. Last summer was extreme, this year, only slightly wetter. So, yeah, the underground springs and water table could be a factor. My spring only flows after rains in this drought, but neighbor up the slope says it generally flows year round. And the watershed is undersized. My hydralic ram and solar pumps will take care of that when we get just a little more rain, enough to keep the micro ponds down in the draw with water. I'm holding out for some wet stuff and hope the pond will eventually seal. Ewest, are you saying that sorted sand, silt, and a little clay would work as well as rich clayey soil? And BTW thanks for the expert contribution!

Over time sorting occurs with various sized particles filling in the space between sand grains thus stopping the movement of water through it. It can be clay , rock , limestone ,ironstone , pond bottom silt or anything else that will form a seal. Not better than clay but as long as it seals the pond - it works.