Downspout into french drain?


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Old 07-12-17, 12:44 PM
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Downspout into french drain?

We're installing a new french drain in our yard. We need it to divert water coming from our neighbor's yard. At the same point in our yard we have a pipe coming from our house's downspout. We want to attach the solid corrugated pipe that comes off of the downspout to the french drain's perforated pipe, which will then attach lower in our yard to another solid corrugated pipe.

My question is: Does having all the water flow from the downspout's solid pipe into the french drain hurt the functionality of the french drain?

Thanks in advance for your advice! We're new to french drains around here.
Rebecca
 
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Old 07-12-17, 01:15 PM
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I understand natural lay of the land, and that some properties are lower than others, so there may be a certain amount of migration from the neighbors property, but downspouts tend to dump a larger volume of water into a concentrated area, and I don't understand why the neighbor's downspouts would be your problem at all. Yes, in general, except in very ideal conditions for this particular situation, it would certainly seem that adding a downspout is going to reduce the effectiveness of your french drain. I would begin a friendly conversation, explain your concerns, and ask the neighbor to look at a solution for dealing with their water.
 
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Old 07-12-17, 01:34 PM
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The neighbor has their downspout directed toward our property so it does not drown out their garden. The french drain is meant to protect a new retaining wall we built for a gravel pad for our new shed from getting too much water all the time. Note, the shed/retaining wall/gravel pad are just feet from the neighbor's yard.

You say the downspout will reduce the effectiveness of the french drain - can you tell me more? Do you presume the french drain will be so filled with downspout water that it won't be able to divert the natural water flow?

The alternative would be to install a solid pipe all the way from our downspout to the bottom of our yard, which is where our shed ends. The whole point is to divert water from the shed. Thus, there will be some kind of pipe in the ground carrying water at least from our downspout. Any reason it would be worse for it to be a french drain vs. a solid pipe. Or, do we really need to install a french drain next to a solid pipe?
 
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Old 07-12-17, 01:51 PM
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The neighbor has their downspout directed toward our property
Your call but in some areas this is not legal and you could work to get them to redirect the water. Around here, we are not allowed to put water onto a neighbor's property (there is a waterway along the backs of our lots, we drain to that).
 
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Old 07-12-17, 01:55 PM
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"You say the downspout will reduce the effectiveness of the french drain - can you tell me more?"

I don't know what your circumstances are, but, as an example, a 1200 square feet home with a half dozen downspouts is going to put about 62 gallons of water through each downspout for every 1/2" or rainfall. So picture more than a 55 gallon drum of water dumped into that single area for each 1/2" of rain. That's a fair amount of water to dump into a single area, unless it flows to daylight farther back. Larger home or fewer downspouts and the volume per downspout goes up; smaller home or more downspouts and the volume goes down. Assuming of course that the downspouts are evenly distributed. If you want to verify, there are of course 144 square inches in a square foot, and there are 231 cubic inches in a gallon.
 
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Old 07-12-17, 02:03 PM
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It is essentially going along the natural grade too, so we definitely need something even if neighbor turns his pipe. The water could still head our direction because of the grade.
 
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Old 07-12-17, 02:07 PM
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Hmmm, this is a lot of good info, but I'm afraid I'm too ignorant on this topic to determine how this should guide our decisions.

Also, the natural grade is such that water flows out of our yard into the yard of the neighbor behind us (not sure if this is related to your "flows to daylight" comment). Thus, we just need to ensure that when the water makes its way there, it doesn't flood our shed area in its path.
 
 

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