OT Outside Drainage Flow Dynamics

D107

We are doing some landscaping work and have had our team install a 390 gallon cultec collector. The intent is to pickup the two house leaders, two garage leaders and two patio drains, all from NDS drain boxes. Two additional driveway drains are not collected but drain directly into the overflow line.

The original drawing shows the house leaders output line Y-ing into the garage output line and then into the cultec which would drain into its other end and run across into the driveway and culminate into a pop-up drain when the cultec was full. That made sense to me.

A change was made at some point —not sure why—to not run the line out of the cultec's other end but to allow the overflow to build at the front end of the cultec into an overflow line that is six inches higher than the pipe meeting it and then connect with a driveway line.

The benefit of those six inches is supposed to be that the volume capacity of the cultec is expanded to a greater amount. I have had verbal explanations of this but the explanations don't seem complete—I think I need a revised diagram. So my explanation here may not be a correct one of what is intended. If this all seems sound, I'm happy to just chalk it up to my lack of knowledge and understanding about how these things work.

My problem with this is: What discovered problem is this new design meant to correct? Does it save some trenching of the original line to the driveway? And furthermore, can one assume that when the cultec reaches capacity, the outgoing pressure and weight of the water will force the water level to rise the 6" into the overflow pipe—having created extra capacity?

There is an atmospheric break from the leader into the drainbox. So how do I know that the resistance from the filled cultec is not stronger than the pressure of the incoming drainage—and that the leaders, with no more space to drain into—won't simply pour the water onto the ground and raise the water level 6" into the overflow line?

I should mention that based on roofs' square footage of house and garage, the total water shedding from a 1" rainfall would be 860 gallons; 215 gallons from a 1/4" rainfall. Our soil is very porous sandy soil, so the estimate was made that this system over a 12-hour rainstorm could handle this. Not to mention the capacity of the 1/8" pitched 4" drainage tubing. Also note that the cultec unit is supposed to have 18" clearance above it but in this case it has at least 24".

Jamie Hall

It's all a matter of relative elevations. Much as we might like it to, water doesn't flow uphill. What matters is that the elevation of the overflow — wherever in the basin it is located — is lower than the elevation of whatever catch basins or other inlets there are.

Where it is in terms of location in the basin is irrelevant — all that matters is the elevation.

mattmia2

What you need is an elevation drawing.

D107

There's a conundrum here: it doesn't seem possible to use the same port for both the input to and output from the cultec well, since incoming pipes from house and garage have to be pitched 1/8" per foot drop in to fill the well, and outgoing pipes have to be pitched 1/8" per foot below that in order to drain, which is the way I assume the drawing shows that original output. But using same port for incoming and outgoing is asking water to move in both directions.

mattmia2

If the overflow in the inlet is lower than the leader connections, it won't flow out of the tank when the tank is full but will flow out of the overflow instead of in to the tank. regardless of where the overflow is, it has to be able to handle the full flow of all the sources. once it comes up from the inlet, that has to remain lower than the inlets at the downspouts and such and it has to slope continuously down from that inlet. also note that it will kind of saturate the soil or gravel around the dry well up to that high point in the overflow.

hot_rod

It looks like Cultec has some good online help as well as a tech support phone line.

https://cultec.com/

You mentioned a change was made at some point?? By your team or the Cultec design? Find out the how and why of the change decision.

It seems like this is just an enclosed retention pond

D107

I don't know if Cultec was used for any design work; the party involved is experienced and has done other cultec units. I think I have to get a clear idea of the design change which was only explained to me verbally kind of after the fact. Luckily the the overflow and garage piping is not complete yet and there is time to figure this out. I'll also have to wrap my head around Matt's latest description. I've tried but have been unable to get through to Cultec—they put you on hold. But I also need to be able to accurately describe the setup.

hot_rod

A tip from a long time tech support person... A txt or e mail may work better and you have the answer or info documented. If you get voice mail tell them you sent an email for help.

Facetime is another good communication mechanism if you can get through. They will have questions, first off I would want to know who did the design.

It doesn't seem like an overly complicated concept?

D107

@hot_rod and @mattmia2 Thanks.