Backflow in landscape drain

[steadyhand]

I have an outdoor patio that is about 2 feet below the rest of the yard surrounding my house. Because the patio cannot thus drain out above its level, it drains out about 75 feet away at a location where the yard is lower than patio level. The drain is 3 inch PVC all the way. There is a neighbors fence very close to the drain exit point, and the city stormwater drain is in the neighbors yard.

Everything works fine when the rain is light with water from the patio existing nicely from the drain end, then going under the neighbors fence into the storm drain.

However, when it rains heavily (over 1-2 inches an hour), the area around the storm drain and my side of the yard starts ponding big time. So much so that I notice that water level on my patio starts increasing to a point where it can enter through a doorway.

I suspect that there may be backflow from the large ponding that is happening near the storm drain. what are good solutions in this case? Some options I can think of are:

1) work with neighbor and somehow try to re-grade the entire area and see if water flows better and does not allow ponding. However, I am not sure if we will hit some upper capacity limit of city storm drains anyway where it cannot drain that amount of water any faster. I am not even sure the neighbor would want to do extensive regarding on his side on my behalf. I may need to get the city involved, but I need to be sure this will work. This is my last resort as it is fairly involved and contentious.

2) Use some kind of a backflow prevention device so that water can only go to the exit point not come back. I am not sure a check valve will work as once its opened in one direction due to water flow, it will likely stay open anyway because there will be more water wanting to go through, before water reverses direction at some point. If such a device can work, should it be at the drain emitter (easier to dig around) or or at the patio drain point (difficult to change much because of a concrete surround). Does anyone have experience with such devices (such as a duck bill valve) for landscape drainage?

I am surviving for now by using sandbags and a pump that kicks on when water reaches a certain level. But I feel that surely there must be an easier solution. I could just plug my patio drain completely (let water flow through from the patio to a sump pump inside my house), but that takes away the good it does for 95% of the rains when not heavy. Also, if the rain becomes heavy, my sump will have the extra work of dealing with water from the outside.

 

[Bgard]

what is the elevation change between the inlet at the patio and the outlet by the fence?

 

[Sponsor]

 

[steadyhand]

what is the elevation change between the inlet at the patio and the outlet by the fence?

It's difficult to say precisely for me without any tools, but is no more than 1-1.5 feet from what I can guestimate. It is also possible that with settling, the slope of the pipe may not be uniform throughout. The way my yard is, there is no other lower point where this water can be made to exit as well. To add, I had the drain jetted once two years back because I though the rate of flow is low. It is still on the low side, perhaps because the elevation change is not a lot. In fact if I put a hose in at full pressure, water will eventually backup (not sure if that is because of line slope or water pooling around drain exit).

 

[Bgard]

did you use schedule 40 pvc pipe or schedule 120 sewer and drain pipe?

 

[steadyhand]

I have never seen it; I bought the house two years back and it was there. I have had plumbers use the term 3" PVC before. I would guess it is the schedule 40 pvc pipe.

 

[Wrenched]

Hello steadyhand,

I'm not sure a backwater valve by itself would help in your situation. Although it would prevent water at the area where it is pooling from flowing back to your patio, the pooling water would also prevent the water from your patio from draining.

I can't see the discharge side in the pictures, but if the height of the pooling gets above the height of the patio drain, then water will naturally flow to the patio. The solutions to this are either to prevent the pooling by regrading the area around the storm drain or by installing new drainage (e.g. a new storm drain), or by installing a backwater valve and secondary drainage or pump system for the patio. The backwater valve can go anywhere in the drain line if it is intact solid pipe. The 3" is probably a sewer pipe rather than schedule 40, which is quite a bit more expensive.

If the height of the pooling does not get above the height of the patio then there is either too much water for the pipe (which is unlikely), or a restriction in flow ( e.g. a root intrusion, or break in the pipe). If when you test it, water backs up without any water pooling at the discharge, it might be worth have the line inspected with a sewer camera.

Good luck!

 

[Bgard]

if you can get water to back up with a garden hose you must have an obstruction of some kind. I have seen the 120 sewer and drain pipe get crushed almost flat from just the dirt compacting around it. with the type of fittings that I see it is most likely 120 sewer and drain see if you can get someone with a camera to look inside of it.

 

[steadyhand]

Thanks. I believe both (water level and restriction) are a possibility. I have seen a lot of water pooling on the patio, which has to be more than just the rain collecting. This must be the level near the storm drain rising above the patio drain.

A restriction is also possible as leaves do get into the drain; could it also be not enough elevation change?

Also, there is a location where this drain pipe merges with another line (from a roof gutter) and flows towards the exit together as one pipe. If there is a restriction after the merge, perhaps the roof water is diverted back to the patio (explaining the surge in water levels).

I had a camera done from the patio drain to the joint (just before the joint) and from drain exit to joint backwards. Both looked clear. We could not get to see what is happening at the joint however as the line would not curve/bend enough to go through. A slow flow from the joint to exit, coupled with gutter water diverting to patio may be a possibility.

I know I have to spend some money here to fix it; am just trying to see what would be the most likely cause so I can solve it without having to eliminate them all one by one.

A backflow preventer will atleast make reverse flow impossible helping in 5% of the high rain situations in preventing backflow..