A heavy storm changes a dam. Not always in ways you can see right away, but often enough that a quick look after the rain stops is worth the time. This isn’t the same as a routine seasonal check. It’s a focused look at what the water just did.
For municipalities, lake associations, private owners, and facility managers, a dam inspection after major rainfall has one job: find what’s different from before the storm, and write it down while it’s still fresh.
What Heavy Rain Can Change Around a Dam
A routine check looks at the dam as it normally sits. A post-rainfall check looks at what just happened to it.
Water levels may sit higher than usual, or drop fast after a spillway opens. Runoff paths that were dry before can carve new channels across the embankment or nearby ground. Surfaces that were covered in grass or gravel may now show bare soil, small gullies, or shifted material.
None of this makes sense without something to compare it to. If you have older photos or past inspection notes, pull them out. A slope that looks a little different might be nothing, or it might be a real change. You won’t know unless you compare it to what the dam looked like before.
Walk the whole structure, not just the parts you remember having problems. Storms don’t always hit the same spot twice.
Embankment Areas That Deserve a Closer Look
Start at the top of the dam, the crest, and work your way down both slopes.
Look for:
- New erosion or bare soil that wasn’t there before
- Depressions or low spots that seem to be sinking
- Cracks running along or across the slope
- Sloughing, where a section of soil has slipped downward
- Paths where fast-moving water cut across the surface
If you spot something, don’t just note that a problem exists. Write down exactly where it is. Measure it if you can, even roughly. Take a photo with something in the frame for scale, like a shovel or a water bottle. A note that says “erosion near the north end of the crest, about eight feet long” is far more useful later than “erosion on the slope.”
This is an observation step, not a soil analysis. You’re not diagnosing why the ground moved. You’re recording that it did, so a qualified person can look at the full picture later.
Spillways and Outlet Features After the Water Moves
Spillways and outlet structures do the hard work during a storm. After that work is done, check them.
Look at whether the spillway channel is clear. Heavy runoff often drags debris, branches, and sediment into these areas, and that buildup can block flow the next time it’s needed. Check for erosion around the spillway edges or beneath outlet pipes, since concentrated flow can wear away soil fast.
Also look for anything that’s moved. Riprap, small rocks placed to control erosion, can shift or wash away in strong flow. A grate or trash rack might be bent or partly torn loose.
Your job here is to notice the problem, not fix it. If a spillway is partly blocked or an outlet structure looks damaged, that’s information for the person responsible for repairs or for a dam professional, not something to sort out on the spot.
Seepage, Wet Spots, and Other Changes Worth Documenting
Seepage is water moving through or under the dam instead of over it. Some dams have small, stable, longstanding seepage that’s already known and watched. What matters after a storm is anything new, or anything that looks different from what’s normal for that dam.
Watch for:
- Wet or muddy spots on the downstream slope that weren’t there before
- Water that’s cloudy, discolored, or carrying soil
- A seep that’s flowing faster or covering a bigger area than before
- Water showing up somewhere it never has
Write down where you saw it, how big the area is, and what the water looked like. A photo next to a stake or marker helps you track it over the following days.
If the seepage looks cloudy or is carrying soil, or if it’s clearly growing, don’t wait. Reach out to a qualified dam professional. Cloudy or muddy discharge can mean soil is being carried out from inside the embankment, and that’s not something to watch and wait on. You don’t need to know the cause to know it’s time to call someone. This is a spot-and-report situation, not a spot-and-fix-it-yourself situation.
Turning a Post-Rainfall Inspection Into a Useful Record
A single walk-through is only half the job. What you do with what you saw matters just as much.
Take photos from the same spots every time you check the dam. Standing in the same place, facing the same direction, makes it much easier to compare one visit to the next. Note the date, the weather, and roughly how much rain fell. Write down water levels if you can read them from a gauge or a fixed marker.
For each thing you noticed, record three things: what changed, where it changed, and whether it looks worse than the last time you saw it. That third point matters most. A crack that hasn’t grown in two months tells a different story than one that’s a foot longer than last month.
Municipalities and lake associations benefit from keeping this in one place, whether that’s a simple folder, a shared drive, or a logbook at the site. Private owners can do the same with a phone and a notebook.
If your notes show something growing, spreading, or new since the last storm, that’s the signal to bring in a professional dam inspection or engineering review. A post-rainfall check isn’t about making that call yourself. It’s about catching changes early and having a clear, dated record ready for whoever needs to look at it next.