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.
