I am trying to make a concrete drainage ditch which will run the length of our property. This is the first time I have done this and probably should get somebody in that has done this before but...........

I know how to build the forms for the vertical walls but how do I get a slope in the middle? Tried to google but cant find anything - anybody done this? have a link?

thanks

We had a 600mtr drainage ditch dug along one wall, no forms just blocks linked with steel and cemented in place and screeded over, I think the base of the drain is poured directly on sand.

Any help at all?

We had a 600mtr drainage ditch dug along one wall, no forms just blocks linked with steel and cemented in place and screeded over, I think the base of the drain is poured directly on sand.

Any help at all?

That is a better idea, think i will go this way. Thanks for posting that.

You want to maintain a 0.5-1cm/m slope; measure the length of the property and determine the total drop. Put a temporary post at each end (and any corners along the path). Use a water level to mark the height at each end, and offset down the required drop. Run a string between the two points above the trench along the slope about a half meter above the ground, and note the exact height difference that the bottom of the trench needs to be from the line. Dig. Measure the height along the line in various locations to ensure you have an even slope-- more frequently the more accurate you want to be.

Pour the concrete base an even thickness, again checking reference height to the string, or just using markers set in the concrete.

Keeping an even slope will ensure that water does not pond along the length creating a place for mosquitoes. Having a steeper slope will help prevent dirt from accumulating, to a degree at least.

A quick and effective method to ensure even slope is to stick a small piece of hardwood or similar on the bottom at one end of a builders spirit level. For a standard spirit level one meter long superglue a small block 0.5cm thick to give the required 0.5cm/m slope. The bigger the piece added the greater the slope. Keep the bubble in the middle as usual.

A quick and effective method to ensure even slope is to stick a small piece of hardwood or similar on the bottom at one end of a builders spirit level.

Judging by the angle-of-dangle on the new wall at my step-son's restaurant his builder forgot to remove his small (quite large by the looks of it) piece of hardwood

The Thais use flexible hose filled with water to calculate the fall. It works quite well over longer distances. Use stakes driven into the ground and measure from the top of the stake down. As was already mentioned, the more fall you have the cleaner the ditch will stay.

There are some chaps doing just this outside the office here in Bangalore.

They have some thin-walled cement pipe (looks about 8" diameter) which they are cutting in half with a disc-cutter. The U section then forms the bottom of the drainage channel, plywood forms up the side, stick in a bent coat-hanger in lieu of re-bar, fill with concrete, job's a good 'un