Why does my underground downspout pipe overflow during heavy rain?

Short answer: The underground drainage system can back up when incoming roof runoff exceeds its conveyance capacity or encounters a restriction.

An underground downspout pipe only carries so much water at a time, and a heavy rain can send more roof water into it than it can move. The pipe may be too small for the roof area feeding it, or several downspouts may be tied into one line that cannot carry them all at once. A flat or sagging section slows the flow, and a blocked or partly blocked outlet does the same, so water backs up the pipe and comes out at the downspout connection or the pop-up emitter instead of draining away.

The first thing we check is the outlet, because a pop-up stuck shut, a line ending in a low spot, or an outlet buried under mulch or grass will back the whole system up even when the pipe itself is clear. After that we look for restrictions inside the line, leaves and granules at the bends, and sections where the pipe has settled. In our clay soil, a pipe that was laid flat can lose its fall over time, and that lost fall is often what turns a system that worked in light rain into one that overflows in a heavy one.

What we check in Humble

When we come out to a home in Humble, we look at this up close — the gutter run, the downspouts, the fascia behind it, and where the water actually goes when it rains. If it ties into the rest of the system, we check that too, so we are not fixing one piece while the next piece sends the water right back. See our Drainage Solutions page for what that system looks like when it is done right — and if the fix is really a drainage question, our Drainage Solutions page covers that side of it.
Related reading: Seamless Gutters · Drainage Solutions · All questions · Contact us
Learn more: Texas A&M AgriLife Extension — Green Infrastructure Practices white paper

Frequently asked questions

How do I know where my downspout water should go? It should be carried away from the foundation to a place that can actually take the water and move it on. If it is dumping right beside the house or washing out the yard, the discharge point needs to be reworked.
Do I need a professional to look at it? If you are seeing the signs described above, yes — it is worth having someone look at it in person before it turns into fascia damage, erosion, or water where it should not be. Call or text Orion’s Rain at (281) 504-9998 and we will tell you what we find.
Do you serve Humble? Yes. Orion’s Rain serves Kingwood and the Lake Houston area — Kingwood, Atascocita, Porter, Humble, New Caney, Summerwood, Fall Creek, Huffman, and Eagle Springs. Call or text (281) 504-9998, 24 hours a day.

Related questions

• Why shouldn’t my downspout discharge onto my driveway?
• Why should underground gutter drainage use solid pipe?
• Why shouldn’t my downspout discharge onto a sidewalk?

Get it looked at

If this sounds like your yard in Humble, call or text Orion’s Rain at (281) 504-9998 — 24 hours a day. We will test the system and tell you what is actually wrong, and what it will take to fix it the right way.

Orion’s Rain Smartscapes and Exteriors — (281) 504-9998 — LI0029444