Shoreline Stabilization

Shoreline Stabilization

By Bob Lusk

Different ponds serve different purposes. In the city, ponds may be used for water retention or fire protection. Urban developers use serene, aesthetic ponds or lakes as added value to help attract buyers or to enhance a park system. In rural America, ponds may serve as a water source for livestock or irrigation. Tens of thousands of ponds and lakes have been built for flood protection. And, then there are those bodies of water destined for recreation…whether designed to wrap a smile around someone’s face as they do battle with a big game fish on the business end of a fly rod or to be a safe stop for a flock of migrating ducks.

One battle all these ponds have in common is erosion. Different soils have different physical or chemical qualities. Some soils are more erodible than others. Clay erodes more slowly than silty sand. Still, disturbed dirt mixed with moving water wants to move. Even the best designed ponds with the best construction techniques and compaction need attention to prevent erosion.

That brings us to the topic of shoreline stabilization.

Ask contractors coast to coast and they’ll agree that shorelines need to be stable to prevent long term erosion from wind and wave action.

What they might not agree about is the best way to prevent erosion.

Some agree that most disturbed soils need vegetation as soon as possible as the project is completed. Others will argue that a more permanent approach is a better solution.

Depending on the purpose of the pond, explore, investigate and choose your best option for shoreline stabilization. If you are working with a fishing lake, use plants to your advantage. Look at designing a shoreline wetland area that serves several purposes. Effective erosion control is the mission, but with a diverse stand of native plants that prefer wet feet, a healthy new ecosystem acts as a filter and adds transitional habitat for the lake. Be wary, though. Use vegetation that fits the context of your project and species which won’t be invasive and turn into a management nightmare in a few years. River cane might be wonderful to shore up a receding creek bank, since its roots go deep and the tops reach upward of two stories tall, but for your two acre pond, that plant may be a bit much. Same with cattails. Understand the plants and how they live before you make the choice. Look at plants such as arrowhead, Louisiana iris, pickerelweed or pennywort. While those species might be a good start, there are certainly others that might be a better fit for your situation.

Moving upland, shallow-rooted grasses such as Bermuda may make immediate sense in the drier soils in warmer climates, moving up from the shoreline as shrubs and deeper rooted, brushy plants gain a natural foothold.

For large expanses of bare soils, seeding is a good thing. But, seeds need water. Water moves dirt. If you have the ability to irrigate to germinate seeds, take that choice. But, if you depend on rainfall, all you need is one frog-strangler to wash the seed…and lots of dirt…straight into the pond, just where you don’t want it to be. For just a little bit more money than the seed, buy erosion control blankets. These are bio-degradable fabrics which hold straw, maybe coconut or a composite that roll out over bare soils on slopes. With your choice of grass seeds imbedded in the weave, two good things happen. The blankets, anchored properly, prevent erosion and keep seeds in place to germinate where you want them. Soon, a nice bed of grass sends its roots spreading throughout the soils, effectively preventing that inevitable argument between water and dirt. Then the mat disappears and, almost like magic, a nice bed of grasses grow to do what they do.

Looking for something a little more permanent than greenery?

There are physical erosion barriers as well.

Gabions, rip-rap, retaining walls and bulkheads might fill the bill. Or, consider mixing and matching these permanent materials with green space.

Gabions are heavy-duty, wire baskets filled with rock. These work especially well for steeper slopes. They’re pricey, but where there’s the need and this is the best choice, take it. For the added early dollars, you’ll save in years to come by not having to deal with the dilemma of some other material sliding down the hill into the pond.

The most common material, especially on private waters, to shore up shorelines is rip-rap. Rocks from the size of grapefruits to basketballs are most common. Two caveats here, though. While rock is comparatively inexpensive, pay attention to the freight bill. Also, rip-rap is best placed by hand. Fuel and labor drive up the cost of rip-rap.

One other hint about rip-rap…most contractors place it where prevailing seasonal winds tend to do the most damage, not all the way around a lake. One popular placement zone is along the inside slope of the dam.

Looking more for that trendy “infinity” look? Consider a retaining wall. Retaining walls and bulkheads definitely put a stop to erosion. But, be thoughtful about materials. Yours truly, in a cost cutting effort, used cedar posts wired together and anchored deep into a clay hillside to hold back the force of tons of dirt. It was a good idea…for seven years. Then, last winter, that rustic little retaining wall gave up. The new one is made of steel reinforced concrete-filled blocks, anchored around steel poles buried 30 inches in the dried pond bottom. That one will last much, much longer.

For retaining walls, don’t use materials that deteriorate. Some metals corrode and break down. Avoid cross-ties and other wood, since it deteriorates when contacted with dirt, water and air.

What about existing ponds, out in the country, which just seem to continually erode? Vegetate. If livestock are wading and wearing a path that’s eroding, make a change. Fence off the pond except for a corner where livestock can come to water. Build a vegetated buffer zone at least twenty feet wide, preferably as much as fifty feet, if you can spare it, around the pond. A buffer zone slows water flow, tends to spread it out and filter the water as it makes its way into your pond.

No matter what, pay attention to erosion. You, or someone, spent a nice chunk of change pushing that dirt out of the pond in the first place. Don’t let nature swirl it back in with its wet whims.

 

Bob Lusk is a 32 year veteran private fisheries biologist, traveling the nation helping people design, build, stock and manage private fishing waters. He is also editor of Pond Boss magazine, the nation’s leading journal on pond management. He can be reached at [email protected].