This diagram indicates a charged drainage system. These are sometimes called either a “wet” or a “pressure” system.
With this type of system a section of the pipe always remains full unlike a Conventional System.
As the pipes are under pressure it is essential all the joints in above ground and underground pipework are fully watertight
A neater appearance than having pipes above ground.
Allows you to discharge water at a height above the ground level at the down pipe.
It is more likely to block as the flow through the pipes can be fairly slow and the low points can collect silt. Silt will get deposited at flow rates below 0.6m/sec which will be the situation for most rainfall events.
It is also more difficult to unblock.
Can cost more with excavation and additional inspection fittings .
Potential for mosquito breeding in water unless appropriate screes are installed.
The vast majority of new houses will have a conventional (sometimes called a Gravity, or Open system) storm water drainage system discharging to either:
Public Surface Water Drain – Typically in Eastern States
Soakwells on Sandy Sites – Mainly in WA
With a conventional system like this the pipes are either vertical or at a slope towards the discharge point.
A feature of this system is that when there is no flow all the pipes are empty.
Simple and inexpensive to design and construct.
If well designed, and constructed, the speed of flow in the pipes will prevents silting and subsequent blockage.
This type of system can look very untidy when taking water to a Rainwater Tank that is some way from many of the downspouts (It results in lengths of pipes suspended in mid air)
Difficult to transfer water to a discharge point that is above the ground level of the building, although below the gutter level. A problem often encountered on demolition and rebuild projects and battleaxe blocks.
If you are planning a rainwater tank or are having problems with getting storm water to a suitable discharge point you could consider a Closed System
Sleeper Walls (see this link: Sleeper Walls) Unless they have a plastic backing, or no drainage layer!
Gabions – A steel mesh basket filled with rocks. (see this link Gabions)
With permeable walls the water should seep out anywhere on the face.You still need to put a drainage layer behind the walls. This will ensure that there is a clear path to the seepage points and that any dirt is filtered out rather than staining the face of the wall. It can be worth using a drainage pipe behind the wall as extra security against water pressure building up.
With these walls you need to make special provision for drainage.
Weep holes which are specially constructed holes through the structure at 1m, or less, spacing.
An Agricultural Pipe(a perforated or slotted pipe see this Link Aggi Pipe) discharging to a surface water drain. A good idea is where possible have discharge points with silt pits (see this link: Silt Pit) at both ends of the wall so drainage will still occur if the pipe gets blocked.
For the drainage layer I would recommend at least 100mm of 10mm or smaller gravel.
If you are going to have a pipe the width of the drainage layer should be 50-100mm greater than the pipe diameter.
Use this construction and I don’t think a geotextile is required.
For responsibility for Boundary Retaining Walls see Fairness