Tree Kickers
Tree "kickers" are hardwood logs which are used to deflect stream flow away from an unstable bank area. One or more logs are anchored to the streambank on an outside curve and placed at an angle to "kick" stream flow away from the bank and toward the middle of the stream. Brush is tied between the log and the bank to prevent scour erosion. Kickers are often used with other practices such as evergreen revetments (see Guide No. 12 Evergreen Revetments) which further protect streambanks from eroding forces, and with dormant cuttings and hardwood plantings which reestablish root systems in the bank. See Guides No. 07 Restoring Streambanks with Vegetation, No. 08 Trees for Ditches, and No. 13 Forested Buffer Strips for detailed information on these practices.
A kicker is one of several biotechnical practices described in the Ohio Stream Management Guides. These practices use vegetative or other natural materials to achieve stream management objectives, usually erosion control. One of the chief advantages of biotechnical practices is that they help restore natural stream features, like in-stream habitat and streambank vegetation. Guide No. 10, Biotechnical Projects in Ohio, provides an overview of biotechnical practices. It also maps over 50 project sites and lists contacts who can arrange for site visits.
Some site conditions and/or project objectives (such as protecting existing structures on the streambank) will require use of more traditional, structurally engineered solutions. This is particularly true where high velocity flows can be expected. In other situations, a combination of structural and biotechnical practices may provide both strength and habitat. No project should be undertaken without an understanding of the functions of stream energy and the source of any problem to be corrected. Guide No. 03, Stream Management and the Stream's Natural Processes, will provide an overview of stream dynamics and the impacts land and channel management practices have on streams. Technical assistance about stream dynamics can also be obtained at your local Soil & Water Conservation District. The phone numbers are listed under county government in your local phone directory.
The purpose of this Ohio Stream Management Guide is to describe the generally suitable site conditions and the design, installation and maintenance steps for tree kickers. The guidelines provided are based on years of field experience in Ohio, particularly on Scenic Rivers. As with any construction project in a stream, the Ohio Department of Natural Resources recommends you consult with the applicable local, state and federal authorities listed in Guide No. 06, Permit Checklist for Stream Modification Projects, prior to construction. The extent of permit requirements will depend on the location and design of your project.
Where to Use Kickers
Tree kickers are most often used to correct bank undercutting, especially where the crest of the cut bank is five feet (ft.) or more above normal water levels. A kicker deflects the concentration of stream energy away from the bank. In addition, kickers help rebuild the bank by providing an area for sediments to deposit and provide underwater structure for fish and aquatic insects. The construction guidelines in this Guide apply to this use of the kicker practice. Tree kickers are occasionally used to deflect flows into a point bar on an opposite bank to erode sediment deposits. The sediments will then redeposit downstream where stream velocity slows.
Always look for the cause of erosion when considering how to solve it. If the bank is eroded from flow coming over the bank from adjacent land, kickers are not applicable. If the stream is just naturally meandering, protection measures should not be installed unless really necessary. Tree kickers will not correct erosion due to lack of root structure. In that case, new vegetation should be planted. However, banks which lack vegetation and root structure are vulnerable to undercutting, so a kicker might be needed in addition to the new vegetation.
Channel depth at the construction site needs to be shallow enough for a person to safely stand and work during low flows. Kickers work best where there are trees, preferably live ones, on the bank onto which one or more logs can be anchored. Since the kicker practice alone does not include planting vegetation, it can be used in shady areas. Kickers are most often installed in streams where the channel width is less than 100 ft. but wide enough so that deflected stream flows do not cause erosion on the opposite bank.
Design and Construction Guidelines
Choosing a Kicker Log - Any available tree can be used for the deflecting log, including those found in the channel. In fact, woody debris found in stream channels can be put to good use in constructing kickers. Excess debris (that which is causing an obstruction) should be removed from both the channel and the floodplain. The best species for kicker logs are hardwood trees, which deteriorate slowly, and/or trees with dense branches, which slow stream flow and catch sediments. The size of the log(s) should be compatible with the channel width and stream flow at the site. Of course, the anchor trees should be as large or larger than the kicker log.
Brush or evergreen trees should be cabled to the kicker log in the area between the log and the bank (see Figure 1). Small trees with crowns intact can also be used. This prevents bank scour and traps sediments in the slower, "backwater" area. If the kicker log still has its root wad attached, extra care should be taken to tie brush around the wad on the side toward the bank. Root wads are excellent for in-stream habitat structure but increase the likelihood of bank scour.
Do not anchor the kicker log or the brush to the streambank. During high flows the log and attached brush need to be able to rise with the water. If high velocity flows occur before sediments have a chance to build up and "attach" the kicker log to the bed and bank, those flows may scour under the kicker structure. Choosing logs with large and dense branches helps prevent this scour. Repair or replacement may, however, be necessary. If this is a concern, and the stream size and project design allows the kicker log diameter to be about 6 inches or less, you can try anchoring the top end of the kicker log into the stream bed or bank to prevent it from floating. Anchoring methods are discussed in Guide No. 12, Evergreen Revetments.