5 Signs Your Stormwater System Needs Repair

Quick answer: The five warning signs are: standing water that persists 72+ hours after rain, visible erosion around ponds and outfalls, sediment buildup reducing pond capacity, damaged or clogged outlet structures, and vegetation overgrowth blocking flow paths. All five get worse over time and cost significantly more to fix the longer they’re ignored. A small erosion gully that costs a few thousand dollars to repair can become a major bank failure costing tens of thousands.

Stormwater systems are designed to work quietly in the background. When they’re functioning properly, you barely notice them. But when something goes wrong, the consequences can be sudden and expensive: flooding, property damage, regulatory fines, and costly emergency repairs.

The good news is that stormwater problems almost always give warning signs before they become emergencies. If you manage a property with ponds, detention basins, or other stormwater infrastructure, here are five things you should be watching for.

If the term BMP keeps showing up in your inspection reports without explanation, our primer on what a stormwater BMP is covers the vocabulary these signs are written in.

1. Standing Water Where There Shouldn’t Be Any

What it looks like: Puddles that persist for days after a rainstorm in parking lots, grassy areas, or around building foundations. Water pooling in a detention basin that’s supposed to drain dry. Soggy, muddy areas that never seem to firm up, even during dry weather.

Why it happens: Standing water is a symptom, not a root cause. Something in your drainage system is preventing water from moving where it’s supposed to go. Common culprits include clogged pipes, blocked inlet grates, failed outlet structures, settling or grading changes that have altered flow paths, and underground systems that have partially collapsed.

In detention basins specifically, standing water more than 72 hours after a rain event typically means the outlet is obstructed. Sediment, debris, or structural damage may be preventing the basin from draining as designed.

What it means: Water that isn’t draining isn’t being treated or controlled. Your stormwater system isn’t performing its function. Standing water also creates mosquito breeding habitat, accelerates pavement deterioration, creates slip-and-fall hazards, and can damage building foundations. If the problem is caused by a blocked or collapsed pipe, the situation will only get worse with each subsequent storm.

What to do about it: Don’t ignore it and don’t assume it’ll resolve on its own. Have a stormwater professional inspect the area to identify the obstruction or failure. The fix might be as simple as clearing a clogged inlet, or it might require pipe repair, re-grading, or outlet structure rehabilitation. Either way, early intervention is far less expensive than waiting for a failure during a major storm.

2. Visible Erosion Around Ponds and Outfalls

What it looks like: Bare soil, undercut banks, gullies, or exposed pipe ends around your stormwater ponds, at pipe outfalls, or along drainage channels. You might notice that the shoreline of a pond has receded, that soil has washed away from around a pipe, or that riprap (the layer of large stones placed for erosion protection) has shifted or disappeared.

Why it happens: Erosion around stormwater infrastructure is caused by concentrated or high-velocity water flow. This can result from undersized pipes, missing or degraded energy dissipation structures (like rip-rap aprons at outfalls), changes in upstream flow patterns due to new development or altered grading, or simply the cumulative wear of years of storm events on unprotected soil.

Bank erosion along ponds is particularly common. Ponds experience constant fluctuation in water levels during storms, and wave action from wind and fountains gradually undercuts the shoreline. Without stabilization measures, the banks erode progressively inward.

What it means: Erosion isn’t just an aesthetic issue. It’s actively destroying your infrastructure. Eroding banks reduce the volume of your pond, meaning it can hold less water during storms. Eroded outfalls can undermine pipes, causing them to shift, crack, or separate. Sediment from erosion washes downstream, potentially clogging pipes and filling other BMPs. In severe cases, erosion can threaten adjacent structures, sidewalks, parking areas, and utilities.

It also tends to accelerate. A small gully becomes a larger one. An undercut bank eventually slumps. The longer you wait, the more extensive and expensive the repair.

What to do about it: Have the erosion assessed by a professional to determine the cause and appropriate repair. Solutions range from installing riprap and erosion blankets to regrading slopes, stabilizing banks with plantings or retaining structures, and repairing or extending outfall protection. The right fix depends on the specific site conditions and the severity of the damage.

3. Sediment Buildup Reducing Pond or Basin Capacity

What it looks like: Your pond looks shallower than it used to. You can see sediment deltas forming where pipes discharge into the pond. The bottom of a detention basin has a visible layer of accumulated soil and debris. Areas that once held several feet of water now barely hold a few inches.

Why it happens: Every time it rains, stormwater carries sediment, including soil particles, sand, organic matter, and debris, from your property and upstream areas into your stormwater system. This is actually by design. Ponds and basins are intended to capture sediment as part of the treatment process. But that means the sediment has to go somewhere, and it accumulates on the bottom over time.

The rate of accumulation depends on the size of the contributing drainage area, the land uses upstream, construction activity in the vicinity, and how well upstream erosion is controlled. Properties near active construction sites or with large areas of bare soil will see sediment accumulate much faster.

What it means: A pond or basin full of sediment can’t do its job. The entire purpose of these systems is to store a specific volume of water during storms and release it at a controlled rate. When sediment fills a significant portion of that volume (a common threshold is 25 to 50 percent), the system can no longer handle the design storm event. Water overtops, bypasses treatment, and flows uncontrolled to downstream areas.

Excess sediment also degrades water quality, smothers aquatic habitat in retention ponds, and can clog outlet structures. Municipal inspectors frequently cite sediment accumulation as a violation during compliance inspections.

What to do about it: Sediment removal, often called dredging or cleanout, is a normal part of stormwater system ownership. It’s not a sign that something was built wrong. It’s simply the reality of how these systems work. Most ponds and basins need sediment removal every 10 to 25 years, though some need it sooner depending on conditions.

The process involves dewatering (if needed), excavating accumulated sediment, disposing of it properly (sediment may contain pollutants that require testing), and restoring the original design grades. This is specialized work that requires knowledge of the original design, proper permitting, and appropriate equipment. For the timing side, see how to tell when it’s time to dredge. For the money side, see our pond dredging cost guide.

4. Damaged or Clogged Outlet Structures

What it looks like: The concrete or metal structure at the edge of your pond, whether it’s a riser, weir, or control structure, has visible cracks, missing components, rust, or displacement. Trash racks or grates are bent, broken, or missing. Water is flowing over the top of the structure rather than through the designed openings. Or the opposite: no water appears to be flowing out at all, even when the pond is full.

Why it happens: Outlet structures are the mechanical heart of your stormwater system. They control how much water is released and at what rate. Over time, these structures degrade. Concrete cracks from freeze-thaw cycles and settling. Metal components corrode, especially in coastal environments. Trash racks get clogged with leaves, branches, and litter. Beavers and muskrats build dams around them. Vandalism and accidental damage from mowing equipment take their toll too.

Internal components like orifice plates, weir walls, and connecting pipes can also fail. These are harder to detect because they’re partially or fully submerged.

What it means: A damaged outlet structure compromises the entire system. If the outlet is clogged or blocked, the pond or basin can’t drain, leading to elevated water levels, overtopping, and potential flooding. If the outlet is damaged and releasing water too quickly, the system loses its ability to attenuate peak flows, which can cause downstream erosion and flooding.

Outlet structure failures are one of the most common findings in municipal stormwater inspections and one of the most common causes of enforcement action. We go deeper on this one in outlet structure failures: warning signs and when to call for repairs, including which symptoms are emergencies and which can be scheduled.

What to do about it: Outlet structures should be inspected at least annually, and debris should be cleared regularly, especially in fall when leaf litter is heaviest. Structural damage requires professional assessment and repair. Depending on the extent of damage, repairs might involve patching concrete, replacing metal components, installing new trash racks, or in some cases, fully replacing the structure. Don’t attempt to modify an outlet structure without engineering guidance, as changes to the outlet directly affect how the entire system performs.

5. Vegetation Overgrowth Blocking Flow

What it looks like: Thick brush, tall grass, woody vegetation, or invasive species growing in and around your stormwater system. Cattails and phragmites choking the edges of your pond. Trees and shrubs growing on dam embankments. Vegetation growing through inlet grates or into pipe openings. Swales that have become so overgrown you can barely see the channel.

Why it happens: Nature doesn’t stand still. Left unmanaged, vegetation will colonize every surface of your stormwater system. Seeds blow in, birds deposit them, and existing plants spread aggressively. Nutrient-rich sediment in ponds and basins provides ideal growing conditions. Invasive wetland species like cattails and phragmites are especially aggressive. They can take over a pond in just a few growing seasons, spreading from the edges inward and eventually filling large portions of the open water area.

What it means: Vegetation overgrowth is more than a cosmetic problem. Plants growing in flow paths, at inlets, outlets, swales, and channels, physically obstruct the movement of water. This reduces the capacity of the system and can cause water to back up or bypass the BMP entirely.

Trees growing on dam embankments are a serious structural concern. Roots can create pathways for water to seep through the embankment, weakening it over time. If a large tree falls, it can tear out a section of the embankment or damage the outlet structure. Most dam safety guidelines prohibit woody vegetation on embankments for exactly this reason.

Invasive species that colonize ponds reduce open water volume, impede access for maintenance, and make sediment removal significantly more difficult and expensive when it eventually becomes necessary.

What to do about it: Vegetation management should be part of your routine maintenance program. Mowing around ponds, basins, and swales should happen on a regular schedule. Invasive species should be treated and removed before they become established. Woody vegetation on embankments should be removed promptly, including the root systems when possible.

For ponds already colonized by invasive species, a targeted aquatic vegetation management plan is typically needed. This may involve herbicide treatment, mechanical removal, or a combination. The goal is to restore the open water area and prevent regrowth.

The Common Thread

All five of these warning signs share something in common: they get worse over time, and they get more expensive to fix the longer they’re ignored. A small erosion gully becomes a major bank failure. A partially clogged outlet becomes a fully blocked one during the next big storm. Sediment that could have been removed with a small excavator eventually requires large-scale dredging.

The most effective approach is regular inspection and proactive maintenance. Walk your property. Look at your ponds, basins, and drainage channels. If something looks different from how it used to look, or if water isn’t behaving the way it should, take it seriously.

AUE Land Can Help

AUE Land provides stormwater system inspections, maintenance, and repair for properties across the region. If you’ve noticed any of the warning signs described above, or if it’s been a while since your stormwater infrastructure was inspected, our team can assess your systems, identify problems, and recommend the most cost-effective path to getting everything back in working order. Contact us to schedule an inspection.