I would be very concerned about that. Groundwater under your liner is definitely not something you want. I can't remember where I saw it, but one ponder designed his pond with a collection pit and sump pump under the liner to deal with just this issue. I would talk to a professional pond builder for some advice before proceeding.

Well I thought this could be a normal situation for people leaving in Pacific North-West since we get lots of rain.

I could pump out the groundwater and lay the liner and fill it with water. Will this be sufficient?

I can't really answer that. If you have a high water table, then the water will just come back. If you can pump it out and it doesn't fill up again, you may be OK. But I would ask someone in your area who has built ponds.

I get seasonal high ground water. At one point my pond was full - before it had a liner. Yes, you run the risk of having your liner float. I have handled it in a couple ways -- First use some of that dirt to make the pond edges higher than the surrounding area. It only has to be a few inches but that keeps surface water from running in and makes for more water in the pond than underneath no matter how high the ground water gets. And make sure you have a few BIG rocks in the bottom of the pond. Cement blocks for pots to sit on also work. I have waterlilies in pots on blocks around the edges and a couple in the middle for a reason - they keep the liner in place. It may float a little but it will settle back in place. Higher sides=deeper pond and keeps more weight/pressure on top than under. That will help somewhat to keep the sides from falling in. I have very sandy soil so I did have to cement the sides of my pond. My pond is 3+ ft. deep at the deepest. All the sides are cement over plastic "chicken wire" and that has worked. Good luck! sherry

Thanks Sherry for a great advice.

After digging all around and due to recent rain the groundwater is more than 1 ft. I am planning to use a centrifugal pump to pump it out.

My question is whether the dirt will clog the pump? How to filter the groundwater?

One more photo

Sherry gives excellent advice however, with the pond built slightly higher than the surrounding ground you will not need any stones to weight the bottom. Never. If your liner floats it's due to your water level dropping below the level of the surrounding ground.

Few weeks back the groundwater was up to the top after heavy rains. Few days back I used a 0.5 hp pump to pump it out. It was taking quite a bit of time.

So I decided to siphon out the water since the storm drain was at a much lower level. I am keeping the siphon on continuously. Will see next week if the water level has gone down.

I will attach more photos in next posting.

Siphoning water by garden hose.

You may have a solution at hand. When I encountered the same situation 8 years ago when building my pond, a considerably lower storm drain was near-by. I put in two connected 4" drainage pipes in a silt sleeve, buried in coarse gravel, connected to my house drainage that went to the street and the considerably lower catch basin. You would connect an overflow drain in the pond at the height of water level, and connect it to the outflow drainage pipe. Two big problems resolved. You might do a little reading on the dynamics of groundwater to help sort out the advice you get.

I have never seen any ballooning in 8 years and overflow or pumping water out of the pond is no problem.

The downside is that connecting the drainage pipes from below the pond can mean a long trench to reach the same elevation as the drainage pipes. It sounds like you have a potentially great location with the much lower storm grate. A little arithmetic will tell you if your on-site grade will work with this system. Of course it might need a small backhoe or big sons.

Back when I built this, even the reliable advisors here told me a drainage system with overflow function was unnecessary, a waste of time, money and effort. Sometimes being stubborn and persistent yields good results.

Good advice on the forum, do your homework and good luck with the situation. Let us know.

Hire somebody with an excavator and get the job done right. He could get rid of those stumps while he's at it. As it is, you have a mud puddle in the middle of nowhere.
With a water table that high you don't even need a liner.
I live in your part of the country (near Maple Valley) on acreage and made a number of ponds in the 'old days' using a bulldozer. Now, with excavators, the job goes much quicker. Most of my ponds go dry in the late summer but by November they are full again. Those are called rain ponds. I mow them once or twice during the late summer I stock those that don't go dry with goldfish because Koi are too expensive to feed to the Kingfishers and Herons.
Having a pond is like having a boat. You get one, you want a larger one. So you might as well go as large as possible the first time. Besides, the bigger the pond, the easier it is to maintain.
I'll start a thread in the Gallery showing some of my ponds. None have a pond liner, pump, or filter.
Mike

This post was edited by mikebotann on Mon, Dec 15, 14 at 2:26

Mike,

What you are saying may not be applicable to me because if the rain stops, than within 3 to 4 days the pit is dry. The groundwater goes somewhere.

So I need liner for the summer. Yesterday I used two hose pipes and could siphon most of the water in 4 hours.

I am planning to remove the stump in the middle and keep the ones all-around. I am now planning to compact the clay layer at the bottom manually so that the groundwater does't come up fast. Will see how it goes.

One of the reasons I moved my pond was due to the liner bubbling up because of ground water. My new pond is higher up on the hill, so I made a french-type drain under it. I had to do all my digging by hand, but it was worth it.