How do you reinforce a river bank?

The most ecological and sustainable method for protecting a river or stream bank is by using natural resources such as living or dead trees, their roots, and/or branches. These trees can help protect and reinforce the bank against the current of the river. A benefit of using trees is they do not increase erosion in other areas along the stream. Live trees will also grow over time, developing deep and strong root systems that add additional protection.

Often, when erosion is severe, alternate measures need to be taken. If additional emergency stabilization or protection is required, it’s still a good idea to re-establish trees and vegetation to create a more long-term solution to the bank erosion.

What are stabilization techniques for erosion control?

Riprap / Hard Armoring

Riprap (a type of hard armoring) has been the go-to method for shoreline and riverbank stabilization for years. This method involves using large natural rock along the shoreline to help protect against erosion. Like with seawalls, riprap can cause issues in the long-term. For example, wave flanking or scouring can occur. Riprap can also be costly.

Bioengineering 

Bioengineering for riverbank stabilization is the use of vegetation to reinforce a riverbank and prevent erosion. Natural trees and plants have deep root systems which help hold soil in place and protect the shoreline from erosion. 

According to the US Army Corps of Engineers, the benefits of bioengineering are: “first, the root system helps hold the soil together and increases the overall bank stability by its binding network structure, i.e., the ability of roots to hold soil particles together. Second, the exposed vegetation (stalks, stems, branches, and foliage) can increase the resistance to flow and reduce the local flow velocities, causing the flow to dissipate energy against the deforming plant rather than the soil. Third, the vegetation acts as a buffer against the abrasive effect of transported materials. Fourth, close-growing vegetation can induce sediment deposition by causing zones of slow velocity and low shear stress near the bank, allowing coarse sediments to deposit. Vegetation is also often less expensive than most structural methods; it improves the conditions for fisheries and wildlife, improves water quality, and can protect cultural/archeological resources.”

There are also limitations to bioengineering. For example, the plants may fail to grow due to weather conditions or wildlife.

TrapBag®

The TrapBag® barrier system can be applied to stabilize the riverbank for temporary, semi-permanent or even permanent purposes when filled with concrete.

How do you build a river retaining wall?

Riprap or retaining walls are built along a bank to help protect it from erosion and absorb wave energy. There are many design methods for riprap including the shear-stress method, the velocity method, riprap gradation, and riprap filter. Each of these methods has different formulas and requirements.

Other types of engineered revetments include gabions and mattresses, sacks and blocks, concrete mattresses, and soil cement.

Gabions and Mattresses

Gabions are wire boxes that are filled with stones and then stacked on slopes.

Sacks and Blocks

Sacks and blocks can be filled with sand and cement or soil and help in emergency stabilization projects.

Concrete Mattresses

Concrete mattresses are concrete blocks that are connected by either steel rods or steel cables. 

Soil Cement

Soil cement are concrete blocks that are used instead of rock.

Retaining Walls

There are three main types of retaining walls for riverbank stabilization, gravity walls, cantilever walls, and sheet piling walls.