I am sure we can all agree that trees are beneficial. They provide oxygen, hold our valuable topsoil in place, give us shade in the hot summer, and beautify our surroundings, not to mention all of the things in our lives that are made from lumber or wood by-products. However, there are occasionally times when trees are a problem — when they create a logjam.
A logjam occurs when woody vegetation obstructs a stream or river, creating a barrier to the flow of water. Logjams are a natural part of stream life providing structure and cover for fish and wildlife. The pool behind the logjam creates critical aquatic habitat during low flow conditions. Water flowing over, around, and through the logjam, stirring and cascading, oxygenates the water. Logjams, because they slow down the flow of the stream, allow for nutrient rich sediment to drop out onto adjacent floodplains.
While logjams may provide enhancements, Ohio’s streams are expected to convey surface runoff from the land in a timely manner. With an average annual precipitation of 38 inches, streams drain away nearly 9.5 trillion gallons of water annually from Ohio, according to A Guide to Ohio’s Streams. Logjams may negatively impact this function because the pool of water created behind the logjam takes up valuable space and retards flow in the stream channel. This results in more frequent out-of-bank events and less natural storage of flood water, adversely affecting farm fields and residences, particularly those in the floodplain or low-lying areas.
Logjams can alter the stream channel. A stream’s energy is channeled toward the route of least resistance, which is often around the obstruction, where it scours away the stream bank to create a new channel. The stream, as it flows through the new channel around the logjam, is then redirected toward the opposite bank. The stream’s energy bounces from one bank to the other, kind of like a pinball game, eroding stream banks and undercutting riparian vegetation. All of the erosion degrades the water quality in the stream, which is deleterious to fish and other wildlife and diminishes or prevents our enjoyment of many recreational activities. This meandering and relocation is particularly destructive in narrow stream corridors running through areas of high development and housing. It can also wreak havoc with subsurface drainage outlets that agricultural producers rely on to improve crop production.
Unfortunately, there is no government agency responsible for logjam removals. The easiest way to handle logjams is to remove them before they become unwieldy and accumulate a significant amount of sediment and debris. Routine inspections of the riparian corridor on your property throughout the year will alert you to fallen trees, debris, and litter that should be removed from the stream and floodplain. Special inspections should also be conducted after large storm events.
Personal safety is of utmost importance when inspecting your stream corridor and when addressing tree and debris removal. Low-flow periods are the best time to conduct such work. Large equipment should not be placed in the stream channel. Any disturbed areas should be seeded immediately to curb erosion. In many cases, bank stabilization may be necessary. Consultation with the county engineer and the floodplain coordinator is recommended. Large logjams that are already well established may need to be addressed by a properly trained and equipped crew.
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Bonnie Dailey is deputy director of the Delaware Soil & Water Conservation District. For information, go to www.delawareswcd.org.