There are several potential problems. I'm going to assume this
agricultural ditch is on your property and you have the right to
manipulate the flow.

You are trying to create a dam and spillway. The dam must be stable
enough to hold back the water, the spillway must be situated so it
does not undercut the base of the dam. It appears there is sufficient
slope in the ditch that you can get at least a 16" rise in water
level.

I can think of several approaches. It seems to me the danger of
undercutting can be eliminated by using pond liner at the point where
the waterfall strikes the bottom of the ditch. I'd start with a 6' x
12' piece of liner. The upstream end would be burried in the muck at
the bottom of the ditch, rise over the blocks, descend over the
downstream end of the blocks, and continue downstream from there.
I'd also buy 4 6' long pieces of rebar, and at least three more
blocks.

Place the first row of blocks in the bottom of the ditch. Trap one
end of the pond liner under the blocks. Drive a rebar through the
center hole of each block, driving it so only 7" extends above the top
of each block. Take the last piece of rebar and cut it into 3 pieces,
then bend each piece into a U shaped 'staple'. The space across the
top of the U will be equal to the wall thickness of the concrete
blocks + the diameter of the rebar.

Now set two rows of blocks on top of the first, one row on the
upstream side of the main rebar, one on the bottom side. Use the
'staples' to hold the blocks in postition. Run the liner up the face
of the upstream blocks, across the top, then down and on downstream.

Another approach would be to purchase about a dozen bags of
Readi-Crete, Quick-Crete, or equivalent product. Stack these to make
a dam (run the length of the bags parallel to the sides of the ditch).
Again, I'd use pond liner to prevent erosion at the bottom of the
waterfall.

PlainBill


On Mon, 05 Jun 2006 17:10:58 -0500, Mama Bear
wrote:

We have an agricultural water ditch running right next to our house.
It's about 4' wide and 3' deep. ( the actual ditch not the water flow )

We thought it would be nice to have some falling water sound in there,
so we could hear it in our yard. So I went and bought 6 concrete blocks
at the store ( 8x8x16 ) and put 3 across the bottom and 3 across on top
of those, but as the water rose in the ditch, the pressure pushed them
all over.

So I put the bottom row back in place and placed the top row back, but
set back a couple of inches towards the water flow, so they wouldn't
topple over. But what that did was create a situation where the water
flows up into the holes in the top row, down into the holes in the
bottom row, and back out through the holes in the bottom row again. It
makes a little waterfall sound but not enough to hear from the house.

How can I do this, so as to keep the water pressure from pushing the
blocks over, and still make the water flow over the top in a nice little
waterfall?

I thought of putting a wood panel up against the blocks from the back,
sort of like a ramp, so the water might flow up and over the top, but
don't know if that would stay in place either.

good point