On Wed, 10 Jan 2018 12:07:17 -0800 (PST), trader_4
wrote:

On Wednesday, January 10, 2018 at 1:45:01 PM UTC-5, wrote:
On Wed, 10 Jan 2018 09:00:14 -0800 (PST), trader_4
wrote:

On Wednesday, January 10, 2018 at 11:43:59 AM UTC-5, wrote:
On Wed, 10 Jan 2018 07:22:40 -0800 (PST),
wrote:

On Saturday, March 13, 2010 at 3:59:18 PM UTC-6, Eric Keller wrote:
My first post to this group so please forgive me if this has been
asked and answered.

I plan on burying my downspouts and having them merge into one 4"
drain pipe. The discharge will be at a nice point far from my house.
The length will be about 200 ft from the first downspout to the
discharge. There will be a total of 4 downspouts merging into the same
line.

My question is: How many downspouts can I run into a single 4" PVC
pipe within the 200 ft length? I live near Chicago and we get plenty
of rain.

Thanks.

At 200' you will be lucky to get 1 to work and even then it will need
to have a pretty good pitch to it.

I don't see why it's such a problem. Sure, it needs proper pitch, but sewer
pipes for example are 4" and support not only clear water but solids too.
Also it's not about the number of downspouts, it's the roof footprint
that they cover. There are probably some online resources that tell you
how much water a given roof will generate during a heavy downpour. It's
not the roof plane area, it's the flat area of ground that the roof covers.
If in doubt, given all the work involved, I'd consider running a 6" line.
Probably be a good idea to have a clean out come to the surface every 50 ft
or so too.

The 200' is the problem. Look at the friction loss (head) in 200' of
pipe. When it comes off the roof it will have plenty of velocity but
that will go away pretty fast in a near horizontal run.

How do typical sewers work then, running down the street? They go a lot
further than 200 ft.

They are a whole lot bigger than 4" and in most places there are lift
pumps unless you are talking about a city on a hill.
Water still moves pretty slow in a sewer or a storm drain.

Hey if he wants to try it, go for it but I doubt he will ever serve
more than one downspout and even then, in a heavy rain, water will
back up in that 4" pipe unless he has a whole lot of slope on the
line. (1/2" per foot or more).
This is just based on what my neighbor found running about 40' of 4".
It could also be it rains harder here I suppose.