Draining the pool cover

[Canucklehead]

I've read the 2016 thread on this subject. My issue is that my (not quite impermeable) winter cover has a large lake, a depression 12" or more deep, that I can't get rid of. The Little Giant™ pump takes the water level down across the entire surface of the tarp, leaving the lake still present.
There is a small amount of fine debris at the bottom of that lake. Not much in terms of weight.
Scratching my head over this issue, which I seem to have managed to overcome in past years. Not so much now. This seems to be disobeying the laws of physics. You'd think the tarp would float perfectly flat on top of the pool.
Anyone? Thanks.

 

[Newdude]

This seems to be disobeying the laws of physics. You'd think the tarp would float perfectly flat on top of the pool.

It will until it’s completely saturated and then it will let more water through (both ways). You end up pumping out pool water through the cover yet the water on top seems unchanged.

It doesn’t hurt anything so pump down to a proper level and whatever is on the tarp is still ‘in the pool’. You may want to add some bleach to the top so it gets less stagnant sitting in the sun. The top water gets nasty pretty quick.

 

[Canucklehead]

Thanks!
The tarp is plastic, so it doesn't get "saturated" according to what I understand that word to mean. The water on top is pretty clean so far, but I will keep in mind what you say about adding a little bleach.
I get what you mean by "still in the pool". Worse case, when time comes to remove the cover, I guess we'll just pull it out from under the lake.

 

[Newdude]

The tarp is plastic, so it doesn't get "saturated" according to what I understand that word to mean.

Its woven plastic and it takes a while for the water to really squeeze all up in there. Its nearly waterproof at first. Once it does, it will pass through the tarp much easier.

 

[Canucklehead]

The answer to my question eventually revealed itself. Once I was able to remove most of the "fine sediment" at the bottom of the lake on top of my winter cover, the cover did rise to lie flat again. I underestimated how much effect a thin layer of sediment can have.