First post, so I'll start by saying hello: Hello!
I have been asked to install a land drain under a lawn by a client. I have only previously installed herringbone patterns, but this is often governed by the shape of the land. In this instance however the area is a near rectangle. Which got me thinking, must it be this way?
I have only found a single reference to a grid system in a Green Keeping magazine whereas every other article deals exclusively with Herringbone.
I have attached two draft layout diagrams. The meterage is pretty much the same and the work involved broadly similar, so I am not necessarily looking to save time or money but is there a reason why one design is better than the other?
One point to note. The garden has a natural fall so the pipe depth can be kept constant for the length.
Thanks in advance for any advice.
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The herringbone pattern is more complicated and slower to install than a grid pattern and the grid is much quicker and easier to install and you can easily fit silt traps to it. And it's also cheaper.
In terms of function, will they operate the same?
The herringbone laterals because it cuts across the slope will have a shallower fall and thus presumably a slower flow rate compared to the long straight length that runs to the soakaway. Would that be beneficial in the sense that the long length is delivering it's water to the soakaway first giving that a chance to start draining before the lateral pipes start delivering water? With the grid, is that not like running three motorways straight into the soakaway.
Or am I over thinking this? I just see the grid format referenced so infrequently in online literature that I feel I must be missing something.
The herringbone pattern allows the pipes to be joined at a 45 degree angle rather than 90 degrees. 90 degree joints slow the water flow more leading to the silt droping out of the water and blocking the drains. For this reason all the landdrain connectors sold as 45 degree junctions. You could possible simply the herringbone design by having the laterals at only one side. Im not sure out the necessity of a silt trap, it's a lot of extra work and I've never come across one in this small a scheme. The big question you do not touch on is where are you going to drain the water too?
Regards,
Mark
Mark,
Thanks for your thoughts.
The land drains are terminating in a soakaway shown, but not identified, on the sketches as the rectangle towards the top. This will in turn has an overflow.
In both instances I'm not creating any 90-degree angles. The Herringbone for obvious reasons and the grid has three drains that run straight into the soakaway and a fourth (on the right) that will join the third at a 45 angle towards the end of it’s run.
It's for this reason that I have shown the soakaway as a long thin strip to accept the grid whereas if I was opting for the herringbone with one main spine I could shorted but deeper soakaway. At present it is just there for illustration purposes until I've narrowed down the preferred option.