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Posted: Fri Dec 19, 2008 10:47 am
by StevieG
I have a rear garden that is hard landscaped with mostly gravel and some slabbing. i have a serious problem with drainage. I was going to add french drains but im not sure where to run water to. I have a surface water drain near the problem area but the pipe is about 350-400mm below the lowest level of the garden. Is this sufficient for a fench drain.
Thanks in advance.
Posted: Fri Dec 19, 2008 10:58 am
by GB_Groundworks
the answer will depend on the length of the drain to ensure there is enough running fall on the drain to carry the water into the surface water drain.
from the main page on drianage
Gradient
All drainage systems, both above ground and below ground, work by creating a slope and relying on gravity to cause the water (or other liquids) to flow from the high point to the low point. This is known as the 'fall' and can expressed in a number of ways, usually either a percentage or as a ratio.
All gradients are defined as the amount of rise (or fall) in height above a fixed point over a given distance (the run). Gradients are expressed in a number of ways, including Ratios [1 in 60 or 1:60] and Percentages [16%] Gradient
For 100mm pipes, the type normally used for residential drainage, the minimum acceptable falls are 1:40 for Foul Water and 1:100 for Surface Water. Larger diameter pipes may have gentler gradients in certain circumstances.
