Stormwater - minimum fall?

[Christopha]

In a closed system you don't need any fall at all as long as the outlet, whether it is to the street or into a tank is lower than the inlet..... at my beach shack the rainwater discharges into a large fibreglass tank which is approximately 45 metres from the front of house downpipe.... sealed with a 30mm difference in height... Ever seen/used a water level??????

[seanr]

You dont need any fall!!!! as long as the gutter is higher than the tank which it is!!! i think by what you are saying . The water will always flow , even the gutter can be dead level . If you fail to clean the gutters doesnt matter what fall you have you will have trouble . So once a month spend 15 mins cleaning them .

[Skew ChiDAMN!!]

The main reason for fall is to scour out any detritus. You don't need fall, but it doesn't take much in the way of sediment to create problems, especially if gal is used in the system somewhere. And PVC weathers badly, so I don't really want puddles lying around in it.

Anywhere there are horizontal drains or gutters running over "internal" areas, I want some decent fall.

Any horizontal runs without easy access, whether above ground or below, I want some decent fall.

Both to reduce blockages (more shed time) and better get the water away from where it can do damage if something, god forbid, breaks.

[Ivan in Oz]

G'Day Ppl,
When we finally do get rain:confused:
it is usually ALL or nothing
With the Downpoors we get,
I'd like to have some decent fall,
else there is too much 'back-up' and the water will overflow out of the pipework where it SHOULD be going into, to flow away.

Result
Flooded ceilings and Decks:mad:

[TassieKiwi]

G'Day Ppl,
When we finally do get rain:confused:
it is usually ALL or nothing
With the Downpoors we get,
I'd like to have some decent fall,
else there is too much 'back-up' and the water will overflow out of the pipework where it SHOULD be going into, to flow away.

Result
Flooded ceilings and Decks:mad:

Sounds like you need an overflow in the system somewhere to cater for this.

[Christopha]

In a "tropical" downpour which we get all over Australia no amount of fall will stop your gutters overflowing.... proper design of the building elements will however ensure that wet ceilings or eaves is not a problem. Gutters should have a fall just so they aren't continually wet which promotes rust and growth of all sorts. Fitting IPs' so that the sealed system can be accessed easily will keep things easily cleaned, in reactive soils fitting a Storm Plastics telescopic joint will sort out that problem and painting with a good quality exterior acrylic paint will stop any weathering of the PVC. My sealed system which is now over 20 years old has never failed, every so often, usually during a bit of heavy rain I pop an IP and let the system flush itself.

[mudguts]

i agree that any fall is good enough....worked a treat for me

[journeyman Mick]

In a "tropical" downpour which we get all over Australia .............

Christopha,
agree with all your other points but I doubt that all of Australia would get downpours of, say, 250mm in 2hrs like you get in a real tropical downpour.

Mick

[seanr]

Doesn't matter if there is no fall , 1:1 or what ever , the water can only escape at the same rate . If your gutter overflows its because the exit point is too small , nothing to do with fall . I thought you guys were Aussies not Kiwis!!!!