My street was cut from the side of a hill, so my back yard is level
for about 20 yards, then shoots up at about 30-45 degrees well into my
backyard neighbor's yard. I am putting a retaining wall into the slope
to have a pond, half walled by the retaining wall and half walled by
the rising slope of the ground.
My question relates to the flexible liner for the pond, and how to
connect the liner and the retaining wall. My working assumption is to
trim the edge of the liner so there is a little (2-3") lip that will
rest on the top of the retaining wall. The wall blocks are about 10"
deep, so I would have 8" of reatining wall top free and clear. I would
glue the underside of the liner to the top of the retaining wall, then
glue the retaining wall caps on top of that. The retaining wall blocks
and caps are concrete (Country Manor). Any problem with that idea? I
presume I can call the liner manufacturer when I buy it to find out
the appropriate adhesive to use on the liner-wall connection, and I
would use standard landscape adhesive on the retaining wall-cap
connection. Caps are 3" high, so the pond water level would be at
least 3" below the top of the caps. The liner would lay against the
sloping (up) ground and I would use large layered stone as the "cap"
on that side.
Ought to work. Before proceeding, though, it might be a good idea to
check and see of you need a building permit and what other
restrictions might apply. Consider effects of major rainfall, for
example, and what happens when the pond overflpws or (heaven forbid)
fails. Have a good plan and you'll get good results
How high does the wall need to be on the low side of the hill for the
depth and width of pond you want to dig? Ten inch interlocking
landscape blocks with no other support may not be enough to hold back
the water. Ponds on hillsides pose a lot of issues not encountered
with level ponds. How much hill will still be above the pond
generating runoff and more groundwater that will flow and scoot under
your liner? I strongly suggest you cut bottom drain in this pond with
a bulkhead and valve that exits below the wall, and lay sand. That
hill will generate water flowage under your liner and that water will
flow under your retaining wall undermining that too. Three inches of
overlap on the edges is not enough in my experience even for a level
pond. Because of that hill and water running under the liner/wall you
are going to have to "overbuild" everything and come up with a
drainage plan to not undermine the walll nor "float" the liner.
Why glue it? I have a similar pond. The EPDM liner lays over the top
of the last course of blocks and is held down by the cap stones. If
you glue and the liner pulls as the pond settles you could tear the
I also have a similar pond built into a hill. The retaining wall is
six courses of about 5" blocks and the liner is held down by 2" caps
with no glue. I'm in Minnesota so the blocks tend to move as the
ground freezes and glue on the liner would be a problem. Go with as
much liner overlap as your caps will allow and you'll be fine.
I put a beach into the hill-side of the pond and the birds love it.
Ten years plus and everything is fine. If you can engineer a bottom
drain that would be good.
all retaining walls fail sooner or later, if yours is holding back
enough water to damage your home or others, be very careful. your
insurance may not cover your loss.
retaing wall must have footer below frost line. i would consult a
engineer, so you dont have future troubles, either because of a
disaster, or a problem at home resale time.
my mother and step dad # 2 had a execvation done for a car parking
area, that later was blamed for a small landslide, that endangered a
engineering and legal fees cost 5 grand......
dont put yourself in a similiar situation:(
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