Streambank Restoration Brings $1.50 Return for Every $1.00 Invested

by Gwendolyn Blanton

Sometimes HRWA gets questions about why we spend so much time working in and along streams trying to fix the banks and improve streamside vegetation. Well, according to the National Research Council, a branch of the National Academies of Science, improving streamside vegetation brings a 150% ecological return on a 100% ecological restoration effort.

Streamside or “riparian” zones are transitions between two habitat types, water and land. Biodiversity, hydrology and wildlife habitat represent the big three ecological functions in these areas. Per acre of land, there are more of these functions in habitat transition zones than in the non-transition zone such as uplands.

HRWA still works every day to improve local water quality policies and planning around the watershed, but we also believe it is essential to get in the river to plant trees that provide shade and bank stability for streams and fallen leaves for aquatic insects.

HRWA’s Volunteer River Restoration Corps (VRRC) has been working hard this past year to improve water quality and bank stability in the Harpeth and Duck River watersheds. In December, Kenny Snyder needed an Eagle Scout project and the VRRC helped him organize a group of 19 Boy Scouts and other volunteers do a stream bank stabilization project via cedar revetments at River Park in Brentwood (along the Little Harpeth River). The Scouts astounded us with their hard work and efficiency! By lunch we had used up our revetment materials and so moved over to Tower Park to do some maintenance work on the tree planting project completed last year. The project also garnered a great story in the Tennessean’s Williamson A.M. section.

In January, four volunteers worked to selectively harvest (cut) and dig (live) cedar and cherry trees for future projects. It rained most of the day, but thanks to their hard work, our February 12th project had plenty of trees ready to be installed.

The February 12th project was in the Duck River watershed at Jerry Erwin Park in Spring Hill and combined our improved cedar revetment techniques with tree planting and bank terracing. The goal was to help the stream rebuild its bank the way nature intended, establishing a stable, vegetated bank with small terraces that allows the river to expand in steps with the rising water.

Here’s how it works:

_ Cedar trees bundled in jute (a fabric similar to burlap) are anchored to the bottom of the stream bank to bring the toe or base of the bank back in toward the center of the stream (see Picture 2).

_ The top of the bank is tilled to allow the loosened soil to be moved down to the top of the cedar revetment. This helps develop terraces in what was previously an eroding vertical bank. The revetment is the new toe and the top of the bank is now a step farther back, much like a line of steps up from the stream

_ The top of the cedar revetment, with all this new soil, is planted with water-loving trees that grow quickly. As the cedar revetment traps sediment inside the jute and between the branches, the new trees send roots down to stabilize the new soil (see Picture 4).

Picture 3: Tilling the top of the bank.

Picture 4: Planting in the soil on top of
the revetment