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Extension How To: Stream Bank Stabilization On An Acre Or Less

By Scott A. Sjolander, Penn State Extension Renewable Natural Resources Educator

This article discusses controlling water’s edge erosion problems on small riparian sites and mentions only a few simple riparian area problems you might consider solving where no hazardous contaminants are involved and no dangers are inherent in the work.

For complex projects or those within specially protected watersheds, consult your local Conservation District, your Penn State Extension riparian specialist, or a qualified design professional for guidance and permitting.

There is no substitute for expert help in resolving water issues, and it’s the law in Pennsylvania.

Stream Bank Erosion

If you have a stream on your property, understanding how streams behave and function within the watershed will be crucial to resolving any problems.

Stream bank stabilization is a collection of vegetative and mechanical methods that can protect critical sections of a stream bank.

Structures are often integrated where standard vegetative practices are not feasible or are not durable enough to provide permanent protection against storm events and stream turbulence.

Streams of all sizes constantly change, shift, and meander. Banks erode naturally as the stream adjusts to changing conditions within the channel and the wider watershed. Human interference can accelerate the changes.

Natural streams are not perfectly straight. Because flowing water tends to meander and move in the soil, sand and gravel, streams naturally alter their channels over time.

Meandering slows the straight-line speed and the scouring action of the stream. Meandering tends to contribute to stream health by creating pools enabling more biotic diversity within.

Stream channels support a variety of living plants and organisms according to zones of wetness and turbulence.

Brown algae, mosquitoes, and snakes are just as important to the aquatic life cycle as water bugs, fish, and larger plants.

Woody vegetation reduces the stream flow velocity, helping absorb energy from drifting debris. Shaded waters stay cooler than open water, allowing more available oxygen to be suspended. Limbs and foliage serve as cover for fish and a habitat for many other creatures.

A stream is only a small portion of a watershed. The watershed also includes the entire drainage area or basin that collects and channels water into a nearby river or receiving water body.

What you do to your stream will impact other plants, animals, and neighbors downstream in the system.

If erosion is occurring in your stream, the banks are usually impacted most. Find out what is causing the erosion above the damaged area.

For long term repair, the cause must be managed or stopped. No repair will be permanent, for water continues to work, moving and depositing with its flow.

Whether the erosion is natural or caused by upstream development, you should consider your impact to the entire watershed when you select a solution.

Banks being undercut need to be stabilized to avoid slumping. Stabilization works by either slowing down the erosive nature of water or by increasing the resistance of the bank to the erosion, or a combination of both.

There are three primary methods used for small stream stabilization: vegetation, rock protection, and bioengineering.

Vegetation

Vegetation may effectively control bank erosion if:

-- The banks are not already seriously eroded.

-- The stream is small and

-- Water velocities are low. A change in flow rate or direction accelerates velocity.

The idea is to establish some sort of “cover” whose root system will hold the soil in place and reduce the impact of flowing water.

There are many methods of establishing vegetation, ranging from reduced mowing to hand seeding to planting to using more integrated solutions.

Live cuttings can be bundled into fascines and pinned along the bank-full water line, or other methods may be used to armor the bank above normal flow level.

Rock Protection

Rock protection involves using large-diameter stones to protect eroding stream banks. Rip rap armors the bank and toe just below the normal water level.

Keying rip rap into the toe of a stream bank is critical when the bottom is subject to scouring or undercutting during storm events.

Stream banks that are to be stabilized only with stone should have a slope no steeper than 1.5 feet horizontal to 1 foot rise.

A geotextile or filter fabric should be used under any stone solution to provide a uniform foundation for the stone. This resists the stone sinking into its substrate and losing its function.

The stone used should be similar to that occurring in the stream bed, unless some further goal is needed. Such might be the case in working to raise the pH of a stream subject to acid seeps or drainage.

As a rule of thumb, stonework should extend up the bank to an elevation where vegetation will provide adequate protection from scouring or erosive forces. The size of the rock needed depends on the velocity of water during expected storm events, with eight-inch rock often used.

Bionengineering

Bioengineering uses woody vegetation like shrubs and trees placed in specific patterns or bundled into fascines for quick anchoring and establishment.

Structures can be formed with live stakes alone. However fabric, or poles, or stone reinforcement may be incorporated in more intensive designs. As the vegetation becomes established, the living structure matures like a natural bank.

Placing stone in wire basket gabions is considered a temporary measure, since the wire will eventually degrade.

Designers use the structure presuming vegetation will have grown large enough to anchor, or other measures will be sufficient to protect the bank when the coir or plastic or wire bindings fail.

Avoid using super-competitive plants from outside the area. Often, these exotics, such as oriental honeysuckles, and some natives such as black locust, take a site over and prove detrimental to valuable native species.

Shy away from planting species you are allergic to or that host animal or fungal pests, or that may be alternate hosts of diseases to your susceptible plants.

Plantings in soils not normally flooded should be mulched for greatest viability. Naturally protective mulch materials can be straw or wood. Pulped, fiberized, or composted wood waste materials make excellent mulches.

Natural mulches conserve soil moisture, suppress weeds, buffer soil temperature fluctuations, and add humus to impoverished soils.

Regulatory codes do not require using specific control methods in a given situation. The designer is free to create and integrate methods in a structure.

Well-designed control structures can improve stream ecology, be efficient in space, and be visually attractive.

Bioengineered projects limited to planting with minimal earth disturbance will require less permitting than those involving excavation.

There is no substitute for expert help in resolving water issues, and it’s the law in Pennsylvania.

Regulatory Bodies

Several governmental bodies enforce code restrictions over private property. There may be particular regulatory codes for work around streams, creeks, wetlands and drainages in your municipality, whether it’s town or country.

Ordinances may prohibit or control the removal of trees or other vegetation from a particular area.

Homeowner’s associations may have covenants in place regulating landscaping or tree removal, fencing, structure size and type and design.

A copy of any covenants existing on the property should be part of the purchase closing package, check further with your local code enforcement officer to be sure.

All plans and actions must comply with 25 PA Chapter 102 erosion and sedimentation provisions. County Conservation Districts administer the permits and design recommendations in Commonwealth as assigned by PA Department of Environmental Protection (DEP).

Any structure or activity which changes, expands or diminishes the course, current or cross section of a watercourse, floodway or body of water require that you comply with 25 PA Chapter 105 procedures administered by the Bureau of Dams and Waterway Management of the PA DEP.

Any modifications involving excavation in the flood plan will probably be subject to Federal regulation under the Clean Water Act.

Your Conservation District will be able to advise you whether your project would require that compliance.

Proposals for modifying the channel, installing structures, or excavating should be presented to the US Army Corps of Engineers for comment and 404 permitting as well as possible 401 clean water certification.

In Conclusion

What you do to your stream will impact other plants, animals, and neighbors downstream in the system. Be sure to consult your experts for help and to maintain legality. Doing so gives you the greatest likelihood of successfully managing your stream conditions.

When you see damage occurring, do not delay in working to find its causes, and considering your options in land use, management, and expense.

Given sufficient space, a riparian buffer of native vegetation is often the fastest and most affordable option.

A first step to consider is to not maintain a mowed lawn to the water’s edge. This means less work and expense for you, and perhaps a reduced problem of goose inhabitants.

It may not, however be sufficiently strong to control your stream bank erosion.

Employing any measure means maintaining your new buffer option to keep it in your desired stage of succession and free from invasive plants.

It may not, however be sufficiently strong to control your stream bank erosion. Seek expert help early on for greatest satisfaction and success.

Acknowledgements

Prepared by Scott Sjolander, Michael Richard Lewis, and Stacy Wolbert. With invaluable guidance from Harvey Pinkerton.

Special thanks go to the Cobb County Soil and Water Conservation District and Georgia Forestry Commission for their inspiration, guidance and review in producing this guide.

Further thanks go to Natural Resource Conservation Service, Penn Soil Resource Conservation and Development, and Crawford County Pennsylvania Commissioner Jack Preston. (Updated July, 2019.)

(Reprinted from Penn State Extension Watershed Winds newsletter. Click Here to sign up for Extension updates.)

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