Guides

Retention pond bank repair: what boards and managers need to know

A retention pond bank is repaired so it holds by rebuilding the slope from the waterline up and getting the grass to root into the bank, not by pushing soil back and laying sod on top. A retention pond is part of your drainage system, not just a view, so an eroding bank fills the pond with soil, moves the edge toward buildings and parking, and can put the property out of line with its permit. The longer the bank is left to slump, the less stormwater the pond can hold.

What a retention pond does for the property

A retention pond holds stormwater during heavy rain and lets it drain away slowly. Roofs, parking lots, drive lanes and lawns all send water to it. The pond was sized and shaped during construction to hold a certain volume, and the property depends on it every time a storm rolls through.

That makes a retention pond different from a lake that is mostly there for the view. When its banks erode, the problem is bigger than how the pond looks. The pond is a working part of the site, and a damaged bank means the drainage system is not working the way it was designed.

What a failing bank does to the pond

• It fills the pond with soil. Every bit of bank that washes in takes up room the pond needs to hold stormwater. Over the years the pond holds less, and the property floods sooner.
• It moves the edge toward buildings and parking. On commercial sites, ponds often sit close to drive lanes, sidewalks and parking. A bank that cuts back toward them puts pavement at risk.
• It can put the property out of line with its permit. Most stormwater ponds were built under a permit that sets how the system must be kept. A pond that has lost its shape no longer matches what was permitted.

Why lost capacity matters

When soil washes into the pond, it settles on the bottom and along the edges. The pond looks about the same from the parking lot, but it is shallower and smaller than it was built to be. In a heavy rain, it fills faster and overflows sooner. Water that used to stay in the pond ends up in parking lots, on sidewalks or against buildings. Many property managers first learn the bank has a problem when a storm floods an area that used to stay dry.

Why the permit question matters

A board or owner does not need to know every term of the permit to see the risk. If the pond no longer has the shape and depth it was built with, it may not match what was approved. What that means for your property, and what the association or owner is required to do about it, is a question for the association's attorney or the owner's counsel. What a manager can do is keep good records of the bank's condition and act before the pond drifts far from its original design.

Why retention ponds erode faster than lakes

The same forces that wear down any lake bank work harder on a pond. Water levels swing more, because the pond is built to fill and drain. Runoff arrives fast and all at once from roofs and pavement. The bank was often graded once during construction and never maintained.

Water levels that swing by design

A lake rises in the wet season and drops in the dry season. A retention pond does that and more, because it is built to fill quickly in a storm and then draw down. The strip of bank between high and low water is soaked and dried far more often than on a typical lake. Grass in that strip has a hard time surviving, and once it dies back, the soil underneath has nothing to hold it.

Runoff from hard surfaces

Pavement and roofs do not absorb water. In a South Florida afternoon storm, all of it heads for the pond at once, often through pipes and outfalls that discharge at the top or middle of the slope. That water cuts channels down the bank and carries soil with it. If the outfall has no protection where it meets the slope, the bank around it is usually the first place to fail.

Banks graded once and left alone

On many commercial properties, the pond was built when the site was developed and has been mowed ever since, with no other care. Mowers scalp the edge, the grass thins, and nobody looks at the waterline until a resident, tenant or inspector points out a problem. By then the bank may have lost several wet seasons of soil.

What to look for on a retention pond bank

Walk the full edge of the pond and look closely at the waterline, not just the lawn above it. Watch for these signs:

• Grass that stops short of the water, with bare sand at the edge
• A small cliff or overhang where the grass meets the water
• Outfall pipes that were once buried and are now exposed
• Channels cut down the slope below drains and downspouts
• Cracks or settling in sidewalks, curbs or pavement near the pond
• Water that stays cloudy after rain

Our guide on why lake banks erode walks through 7 signs of a failing bank in more detail. If you want a quick sense of where your pond stands, the Lake Bank Risk Score asks a short set of questions and gives you a starting point.

How to repair a retention pond bank so it holds

Regrading and laying new sod puts the bank back the way it looked, but nothing is holding the bottom of the slope, so it slides again within a few wet seasons. On a retention pond, where the water swings more and runoff arrives harder, that cycle can be even shorter. We explain the pattern in why regrade and sod fails.

A lasting repair rebuilds the slope from the waterline up and gets the grass to root into the bank. We do this with leading edge technology that lets the grass root into the bank so it holds. The grass grows into the slope instead of sitting on top of it, and the bank gets stronger every year it is in the ground. We do not publish how we do it, but we can tell you what you will see: the work stays at the bank, and the finished bank is a lawn to the water.

There are other options, including rock, sheet pile, geotubes and plantings on a shallow shelf. Each fits a different problem, and some make sense where a pond sits right against a building. Our guide comparing lake bank repair options lays them side by side.

Fix the cause along with the bank

A rebuilt bank lasts longer when the forces that damaged it are addressed too. Ask about protecting the slope where outfalls discharge, keeping mowers back from the water's edge, and directing roof and pavement runoff so it does not run straight down the same path every storm.

How it plays out if the bank is left alone

In the first wet season after the grass dies back at the edge, a pond might lose only a few inches of bank. By the second or third season, the edge has a visible lip and the slope is steeper. After several wet seasons, the bank has cut toward the pavement, outfalls are exposed, and the pond holds noticeably less water. Each season of waiting adds soil to the pond and length to the repair.

How to document the pond's condition

Good records protect the owner or association and let every bidder price the same job. Keep:

• Photographs of each section taken from the same spot, once in the dry season and once late in the wet season
• A site map marking exposed pipes, channels and damaged pavement
• Dates and locations of any flooding the pond did not contain
• A copy of the original permit and pond plans, if you have them

We offer a free lake bank walk where we measure and photograph every section of the pond and give you a written report you can use whether you hire us or not. From that report we build a scope every bidder can price the same way.

Questions to ask a contractor before you approve a pond repair

1. What holds the bottom of the bank after you leave?
2. What happens if a heavy rain comes before the grass roots?
3. How will your work affect parking, drive lanes and tenants while it happens?
4. What does your warranty cover in writing, and for how long?
5. Do you do the work yourselves, or do you subcontract it?

Our work carries a 5 year material and 5 year labor warranty in writing, with inspections in years 3, 5, 7 and 9, each with a written report for the minutes. We do every foot of the work ourselves with no subcontracted crews. If you want to see the result before committing to the full job, we can build a Proof Section of about 100 feet at a spot people can see, with the fee credited to the full job. Call us at (561) 309 9603.

Questions boards ask

Is a retention pond the same as a lake?

Not quite. Many community lakes also handle stormwater, but a retention pond is built mainly to hold runoff and release it slowly. Its water level swings more and faster than a typical lake, which puts more stress on the bank.

Does an eroding bank affect our permit?

It can. Most stormwater ponds were built under a permit that sets how the system must be kept, and a pond that has lost its shape no longer matches what was permitted. Your attorney should advise on what that means for your property.

Can we just dredge the soil back out?

Removing soil that has washed into the pond can restore some capacity, but it does nothing for the bank that is still eroding. If the bank is not rebuilt, it will keep sending soil back in. Our guide on dredging and lake bank repair covers how the 2 fit together.

Will the repair disrupt tenants or residents?

Our method keeps the work at the bank and out of residents' yards. Work is phased by pond or by lake, so the board can schedule each phase around residents.

How do we budget for a pond repair?

Start with a written survey of the whole pond so you know the full length of bank involved. Then phase the work, worst sections first. A scope every bidder prices the same way makes the bids easy to compare.

More guides

• Why lake banks erode, and how to tell if yours is
• Why regrading and sodding a lake bank does not last
• 7 ways to repair an eroding lake bank, compared