Appendix B: Bioengineering for Streambank Erosion Control -- Guidelines
Both Roseboom (1993) and Hoag (1993) advised that willow posts should be long
enough and placed deep enough to reach wet soil during dry summers. Hoag (1993) noted
that plantings can occur at the water line, up the bank, and on top of bank in relatively dry
soil, as long as cuttings are long enough to reach into the mid-summer water table.
An excavator that is either fitted with a long, steel ram or an auger is typically required
for installation. Roseboom (1993) reported that a steel ram on an excavator boom is more
efficient at depths of 6 feet in clay soils. In contrast, an auger on an excavator boom forms
deeper and longer lasting holes in stoney or sandy streambeds. The ram on the excavator is
for creating a pilot hole in which to place the willow post. The willow post is fitted with a
cap that goes over the post and then the heel of the bucket on the excavator is used to push
the post down into the hole. Care must be taken to ensure that the post comes in contact with
the soil so that no air pockets exist. In the case of the auger, this can be done by backfilling
the sides of the hole in lifts and then tamping. In the case of the ram, the ram can be placed
out a few inches from the post and run along the side of it into the soil so as to close the hole
containing the post, especially toward the bottom of the hole.
Roseboom (1993) reported that in larger streams with non-cohesive sand banks, large
cedar trees cabled to the willow posts along the toe of the bank can reduce toe erosion. The
cedars not only reduce bank scour while root systems are growing, but retain moisture during
drought periods. Another material used for the same purpose is a coir roll mentioned earlier.
In addition to trapping sediment, the coir roll can be planted with either emergent aquatic
vegetation or other willow cuttings. The cedar trees and the coir roll were used in
combination with willow poles on Court Creek, Illinois, along a 600-ft reach. Figures 34 and
35 respectively illustrate work in progress and bank conditions four months after planting.
This is described in a case study in Volume II. Velocities were measured at this site during
a major 1995 flood and ranged between 1.23 to 3.11 fps. They were measured at distances
immediately in front of the treatment to 3.5 ft in front and at both the surface and 0.6 d. It
is suspected that the willow contributed substantially to reduced velocities near the bank.
Hoag (1994a) and Hoag (1994b) provided specifications for and description of another
type of implement that is used to make a pilot hole for the dormant willow post. It is called
"The Stinger" and has been used by the USDA Natural Resources Conservation Service
(NRCS) and the Bureau of Reclamation for establishing willow in riprapped revetments on
shorelines of reservoirs and streambanks. According to Hoag (1994b), woody vegetation has
been planted in rock rip-rap in the past, but the methods have concentrated on planting the
cuttings first and dumping rock on top of them or planting through the rock riprap with a
steel bar or water jet (Hoag 1994b cites Schultze and Wilcox 1985).
Hoag (1994b) states: "Neither of these methods are very efficient nor have achieved great
success. 'The Stinger', however, builds upon these methods and utilizes the power of a
backhoe to plant much bigger diameter and much longer cuttings than was possible before.
"The Stinger" can plant cuttings right through rock riprap with minimal effort to better
stabilize the rock, allow the cutting to be above the ice layer, and to improve the aesthetics
B-53
Previous Page
