Water leaves a record. Silt lines, full grates, leaning walls, and four more signs a commercial property or HOA has a drainage problem waiting for winter.
Updated October 2026
You don't need a storm to find a drainage problem. Water leaves a record every time it moves across a property, and in October that record is still sitting there in the dirt, on the asphalt, and at the base of the walls. Our crews read it on every site walk. Here is what we look for, in the order we usually find it.
If you want the broader October walk-through, it's in our full storm preparedness checklist. This post is just drainage, because drainage is where the expensive repairs come from. If you'd rather walk it with us, our teams are doing free property walks this fall across the Central Coast. You can request a free property walk in about a minute.
Walk the low points of the parking lot and look for a faint tan or gray line on the asphalt, sometimes with a crust of fine dirt behind it. That's the high-water mark from the last time water sat there. It tells you two things: water is pooling instead of draining, and the inlet that should have taken it is either too high, too small, or clogged.
What it usually means: a blocked catch basin or a low spot that was never graded to an inlet. What to do: lift the nearest grate (sign 2). If the grate is clear and water still pooled, the problem is grading, and that's a design-build conversation, not a maintenance one.
This is the most common thing we find and the easiest to fix. Lift the grate. If there's an inch or more of soil, leaves, and mulch in the basin, the line below it is probably partly blocked too. If there is standing water in the basin two days after the last rain, the line may have roots in it.
What it usually means: nobody has cleaned the basins since last spring. What to do: a vacuum truck or a crew with shovels for the basins, and a camera run on any line that holds water. Watch the walk-through: Tony covers this one on a real site in about a minute.
Follow every downspout to the ground. If it ends in a small washed-out hole, a dark stain on the stucco, or a patch of bare soil where the plants gave up, water is hitting the foundation on every storm. On a slab building, that's how water ends up inside.
What it usually means: the downspout was never tied into a drain line, or the splash block walked off years ago. What to do: tie it into a drain, extend it at least four feet from the building, or at minimum set a splash block that sends water away from the wall.
Stand at the building and look at where the mulch meets the wall. Years of top-dressing can raise the bed above the top of the foundation slab. When that happens, the soil slopes toward the building instead of away from it, and every irrigation cycle and every storm pushes water at the wall.
What it usually means: a maintenance habit, not a construction defect. What to do: pull the mulch and soil back to at least two inches below the slab line and regrade the first three feet to fall away from the building.
Walk the length of every retaining wall and look at it from the end, not just the face. A bulge or a lean shows up from the end. Then look at the base for weep holes or a drain outlet. If they're buried, crusted over, or you remember them dripping last winter and they're dry now, the drainage behind the wall is clogged, and the wall is holding back water it was never designed to hold.
What it usually means: the gravel and perforated pipe behind the wall have silted up. What to do: clear the outlets first. If the wall is already moving, this needs our design-build team and sometimes an engineer, and it needs them before the rain, not after.
Look at every slope that sits above a parking area, a walkway, a building, or a neighbor. If you can see dirt between the plants, that soil is going to move in a saturating rain. On the Central Coast, we see this most on cut slopes behind buildings and on the uphill side of HOA common areas.
What it usually means: plants died over the summer and nobody replaced them, or the slope was never planted densely enough. What to do: erosion blanket or jute netting now, hydroseed or plugs before November, and fix the irrigation that killed the plants in the first place.
Many commercial properties built in the last 15 years have a bioswale or a detention basin as a condition of their stormwater permit. Walk to the inlet, the spot where the parking lot drains into it. If there's a fan of silt built up there, water is slowing down and dropping its load before it gets into the swale, and the swale is filling up from the front. If water stood in the swale for more than five days after last winter's storms, it is no longer draining.
What it usually means: the swale hasn't been maintained to the permit's schedule. What to do: remove the sediment, check the overflow outlet, and confirm your commercial landscape management contractor is actually doing the swale maintenance the permit requires. On most sites, that obligation stays with the owner.
Take a photo of everything, dated. Sort it into three piles: things your maintenance crew can fix this week (basins, downspouts, mulch), things that need a scope and a price (grading, wall drainage, slope stabilization), and things you want a second opinion on. Then handle the first pile before the next storm and get the second pile priced before everyone else does.
How often should catch basins on a commercial property be cleaned?
At least once a year, before the first fall rain, and again after any storm that drops leaves or debris. Properties with heavy tree cover or a lot of mulch beds usually need it twice a year.
Is standing water in a parking lot a drainage problem or a paving problem?
Usually both. Water pools because the pavement has settled into a low spot and the nearest inlet is clogged, too high, or too far away. Clearing the inlet fixes some cases. If water still pools with a clear inlet, the surface needs regrading or a new inlet.
Who maintains a bioswale on a commercial property?
The property owner, through their landscape contractor, under the conditions of the property's stormwater permit. Most permits require sediment removal and inspection on a set schedule, and the obligation stays with the property when it changes hands.
Can a retaining wall be fixed without rebuilding it?
Sometimes. If the wall is sound and only the drainage behind it has clogged, clearing the outlets and restoring the drain can be enough. A wall that has already cracked, bulged, or leaned usually needs an engineer's assessment and partial or full reconstruction.
Our teams are doing free property walks this fall. You get a one-page photo report of what we found and, if you want it, written options within a day. No pricing at the door and no obligation.
For the rest of the October walk-through, trees to irrigation to documentation, see the full storm preparedness checklist.
K&D Landscaping has been family owned on the Central Coast for 40 years. CSLB #664584.
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