Do littoral shelves stop lake bank erosion?
No. Littoral plants slow small waves and filter runoff, so they can slow erosion on a bank that is still in good shape, but they do not rebuild a bank that has already washed away. If the soil under the grass line is gone, the slope has to be rebuilt first, and plants in the water are at best a partner to that repair.
What is a littoral shelf?
A littoral shelf is a shallow ledge along the edge of a lake, planted with water plants. Many Florida lakes were built with one, and some counties require them on new lakes. Palm Beach County, for example, requires developers of larger lakes in its unincorporated areas to plant a littoral zone with 5 different native species.
The shelf sits just below the normal water level. The idea is that the water stays shallow for some distance out from the bank, so plants can take root there and form a band between open water and the grass slope. When the shelf was built and planted as designed, it can do useful work for the lake. When it was never built, was built too narrow, or has eroded away along with the bank, there is nothing for plants to grow on.
Boards often inherit lakes without knowing whether a shelf was ever part of the design. The original permit drawings for the lake usually show it. Your manager or the developer's engineer may have a copy, and the water management district or county may have one on file. It is worth finding before anyone proposes planting.
What littoral plants do well
Littoral plants have real benefits, and a board should understand them before deciding for or against them.
- They slow small waves before they reach the bank.
- They slow and filter runoff coming down the slope.
- They help keep sediment in place along the edge, which can improve water clarity.
On a healthy bank with a gentle slope and a shelf at the right depth, a band of plants can reduce the daily wear at the waterline. They can also give fish and birds some habitat, and many residents like that. For a lake with water quality complaints, the filtering effect along the edge can help as part of a wider plan.
What littoral plants do not do
The problems start when littoral plants are offered as the fix for a bank that is already failing. These are the limits a board should keep in mind.
- They do not rebuild lost bank. If the soil under the grass line is already gone, plants in the water will not put it back. The slope has to be rebuilt first.
- They need the right depth. Most littoral plants grow in water up to about 2 to 3.5 feet deep. A lake that drops off steeply at the edge has no room for them.
- They change the view. Residents who bought a home with a lawn running to open water see a band of plants instead. In many communities that takes a vote, and it is often unpopular.
- They need ongoing care. Plants die back, get eaten or are crowded out by invasive species, and have to be replaced. One Florida district reports spending about $1,900,000 on littoral plantings, replacements and restoration over the years.
Why plants cannot fix an undercut bank
Most bank failure in South Florida starts at and just below the waterline. The water level rises and falls through the wet season, runoff carries soil down the slope, and small waves cut into the soil under the grass. Over time the bank forms a lip of turf with nothing under it. When that lip collapses, the bank has moved back toward the homes. For a fuller explanation, see why lake banks erode.
Plants placed in the water in front of that lip do nothing for the soil that has already been lost. The slope above them is still too steep, and the grass at the top is still hanging over a gap. The next heavy rain sends more soil down the face of the bank, often right through the new planting.
Why depth matters so much
A bank that has eroded for years usually leaves the lake deeper at the edge than it was built. The shelf, if there was one, may have washed out with the bank. That means there is no shallow ground for plants to hold onto. Planting in water that is too deep usually ends with plants that float away, drown or never fill in, and the board pays to replace them.
How a littoral planting plays out over several wet seasons
Boards are often shown a planting on the day it goes in. A fairer test is what it looks like after 2 or 3 wet seasons.
In the first season, new plants are small and patchy. Water levels rise from May through October, and some plants end up deeper than they like. Ducks, turtles and other wildlife eat some of them. Invasive plants move into the gaps.
In the second and third seasons, the plants that survived either fill in or thin out. If the bank behind them was not rebuilt, the erosion continues above the planting. The board starts to hear 2 sets of complaints: the bank is still caving in, and the plants block the view.
By this point the association is paying for plant replacement, for weed control along the band, and for the bank repair it put off. That is the pattern a board should try to avoid.
When should a board use littoral plants?
Littoral plants work best as a partner to a rebuilt bank, not a replacement for one. These are the situations where they tend to make sense.
- The bank is sound, or has just been rebuilt to a stable slope.
- The lake has a shelf at the right depth, or the permit requires one.
- Residents along that lake have agreed to see plants instead of open water.
- The association has a budget line to maintain and replace them every year.
Where residents want open water and a lawn to the edge, a rebuilt grass bank holds on its own. We rebuild the slope from the waterline up with leading edge technology that lets the grass root into the bank so it holds, with or without plants in the water. If you are weighing littoral plants against other repairs, our guide to the repair options compared sets them side by side.
What a board should look for before approving a planting
A planting proposal should answer a few plain questions. If it does not, ask before you vote.
| Question | Why it matters |
|---|---|
| Is there a shelf at the right depth along this bank? | Plants need water of about 2 to 3.5 feet or less to grow. |
| Is the bank above the planting stable? | Plants will not stop a slope that is already caving in. |
| Does the county or permit require a littoral zone here? | Some lakes must have one, with a set number of native species. |
| Who replaces plants that die, and how often? | Replacement is an ongoing cost, not a cost the board pays once. |
| Have the residents along this lake been asked? | A band of plants changes the view from every yard behind it. |
Questions to ask the contractor
- Which species will you plant, and are they native?
- How deep is the water where each plant goes, and how did you measure it?
- What is the survival guarantee, and for how long?
- What happens to the planting if the bank behind it keeps eroding?
- Who controls invasive plants in the band, and is that in your price or someone else's?
Common mistakes boards make with littoral plants
The first mistake is planting in front of a failing bank and calling the erosion fixed. The bank keeps moving, and the board loses a season or more before it admits the problem.
The second is planting without asking residents. A board can spend money on a planting, then face a petition to remove it because owners did not want their view changed.
The third is treating plants as something the board buys once. Plants are living things. They need care every year, and the cost of replacing them belongs in the operating budget. Our guide to budgeting and phasing a lake bank repair covers how to plan for that.
The fourth is not checking what the permit or county requires. Some lakes must keep a littoral zone. Others never had one. Knowing which applies saves the board from an argument with a regulator later.
How to document the decision
Whatever the board decides, put it in the minutes with the reasons. Include the condition of the bank, photos of each section, whether a shelf exists, and what residents said. If you plant, record what was planted, where and when, so the next board can tell whether the planting worked.
The Lake Bank Risk Score gives the board a quick first read on how serious its erosion is before it spends money on plants or repair. For a full record, our free lake bank walk measures and photographs every section and gives the board a written report it can use whether it hires us or not.
Questions boards ask
Will littoral plants stop our bank from caving in?
Not if it is already caving in. Plants can slow small waves and runoff, but they cannot put back soil that has washed away. The slope has to be rebuilt first, and plants can then be added if the board and residents want them.
Does our county require littoral plants?
Some do. Palm Beach County, for example, requires developers of larger lakes in its unincorporated areas to plant a littoral zone with 5 different native species. Check the original lake permit and ask the county or water management district what applies to your lake.
Can we rebuild the bank and keep open water?
Yes. A grass bank rebuilt to a stable slope holds on its own without plants in the water. We rebuild the slope from the waterline up so the grass roots into the bank, and residents keep a lawn running to open water.
Why do our plants keep dying?
The usual reasons are water that is too deep, wildlife eating the plants, invasive species crowding them out, or a bank that keeps eroding behind them. Most littoral plants grow in water up to about 2 to 3.5 feet deep, so measure the depth before replanting.
How do we see how bad our banks are before deciding?
Start with the Lake Bank Risk Score for a quick read. Then book a free lake bank walk, where we measure and photograph every section and give the board a written report. The board can use that report to compare plants, repair or both, with whoever it hires.
Sources: Palm Beach County ERM, lake excavation · Town of Miami Lakes, lake water quality best practices · Brooks CDDs, lake bank restoration and littorals · UF IFAS Brevard, lake or pond management
More guides
Start with a free lake bank walk
We measure and photograph every section of your bank, and you get a written report you can put in front of the board. It is yours to use whether you hire us or not.