By Roger Lowe,
Professional Engineer, October 1998.
In King County, Washington, USA, a log 30 feet long with a root wad is used. The log is buried in the river bank, with the root wad projecting up to 12 feet into the current, and angled upstream. These are usually placed on the outside of a bend in the river, where the current would normally carry a person toward the root wads.
Root wads is also spelled as one word; rootwads. Root wads are one kind of LWD.
Pictures of root wads will be added to this site soon.
Q. What is LWD?
A. LWD is an acronym for Large Woody Debris. It is a very broad term. The term is used in fisheries biology to indicate wood naturally occurring or artificially placed in rivers. When used to describe wood in rivers, it normally means any piece of wood or collection of wood greater than 6" (15 cm) in diameter, or greater than 10 feet (3 meters) in length. Some researchers consider wood larger than 10 cm in diameter and more than 2 meters long to be LWD.
Q. What is LOD?
A. LOD, or Large Organic Debris is another term for LWD; see above.
Q. What is a "log jam"?
A. A log jam is a collection of wood in a stream that partly or completely blocks the stream flow. It is also used to describe a collection of wood that accumulates along a stream or river bank, or on a gravel bar, bridge pier or other obstruction. A log jam is a form of LWD.
Q. Does LWD kill people?
A. Yes! Many injuries and deaths occur every year because of LWD, root wads and log jams in rivers and streams. In 1997, at least 4 deaths in western Washington State were associated with LWD. A woman was killed by LWD in Idaho in May of 1998.
LWD, root wads and log jams frequently act as strainers, which allow water to pass but will hold an object such as a person. Also, water often passes under the LWD or strainer. Since a person in water is 95% or more submerged, they will be carried with the water, and swept under the LWD or log jam.
Very few people recognize the very large force that moving water can create, and do not realize the hazard associated with LWD or log jams.
Streams and rivers are widely used for recreation. Fishermen, boaters, swimmers and naturalists all appreciate and use streams and stream corridors. Children often play in an around streams and rivers. As a result, people will be exposed to the hazard created by placing LWD or root wads in rivers, and injury and death will occur.
LWD, root wads or log jams intentionally placed in rivers and streams will increase the likelihood of injury or death.
Q. Why is LWD placed in rivers and streams?
A. Some fisheries biologists and others believe that LWD can be a benefit to fish. Also, some people believe that LWD provides erosion protection for stream banks.
LWD and log jams can redirect stream currents, and are a factor in creating new channels, blocking existing channels and creating or destroying gravel bars. In some cases they can create pools.
In western Washington State, grants of money are available to incorporate LWD and log jams in streams and rivers. This provides jobs and opportunities for academic work. In some cases, Indian tribal interests, or state fish and wildlife biologists are making the use of LWD a condition to obtain a permit for in stream construction, including repair of damaged dikes or bank protection.
Q. Is all LWD dangerous to people?
A. No, if the current is sufficiently slow, people can avoid the LWD or extricate themselves. The lethal velocity has not been determined, but some knowledgeable people believe that it is fairly low, on the order of one mile per hour (45 cm per second). Studies are needed to determine the lethal velocity.
Q. What localities are using LWD and root wads in rivers or streams?
A. Several government agencies are using or experimenting with the use of LWD and root wads. There is considerable use of LWD and root wads in western Washington, USA, and some in Oregon, USA, British Columbia, Canada, and in Australia.
King County, Washington, USA, makes extensive use of LWD and root wads. King County has placed about 800 root wads along more than a mile of river bank.
Snohomish County, Washington, USA, has constructed seven log jams on a section of the North Fork of the Stilliquamish River. This section of the river is heavily used by boaters, fishermen, swimmers and children without adult supervision.
Q. How does King County deal with the hazard related to their use of
rootwads and LWD?
A. King County officials deny that there is any hazard, although in some cases they have placed signs on the river bank stating "logs ahead".
King County also consults with a Boater Safety Advisory Committee, but does not necessarily follow the advice of the Committee.
On some projects, King County has placed LWD behind rock spurs or in eddies where the current is normally slow. However a very large proportion of King County's placements are in faster moving water or includes wood projecting into the current.
On some sites, King County has incorported "sweepers" in their construction. A sweeper is a log in the water with water flowing over and under it. They are nearly impossible to see from the water. They "sweep" through the flowing water and sweep up an object such as a person, that can bend around the log. This is one of the most deadly forms of LWD.
Q. How hazardous are King County's placements? A. Many knowledgeable people believe that some are extremely dangerous and will kill people.
There are no know deaths on King County construction as of September 1998, however there have been accidents that likely would have resulted in death except for skilled rescues.
Drawings from King County's design manual, an environmental checklist, and for some construction on the Green river are shown below. Click on the drawings to view a full screen copy of the drawings.
Photographs of recent construction will be added as soon as possible.
From King County's
Many people have protested verbally and in writing to King County oficials that King County's placements of LWD and root wads are dangerous.
Q. Can I examine some LWD installations?
A. Yes, there are many accessible locations on the Green, Cedar, Tolt, Skykomish, and Snoqualmie Rivers in King County, Washington, USA. More specific information on the locations will be posted on this site soon, or email the Webmaster.
Q. Can I contact King County Washington concerning their viewpoint
or explanation concerning their LWD installations?
A. You can contact King County through their website, http://www.metrokc.gov. The King County Executive is Ron Sims. His office may be reached at: (206) 296-4040. His address is: King County Courthouse, Room 400, 516 Third Ave. Seattle, WA 98104, USA. His email address is email@example.com, or click the following link, RON SIMS
The director of the department primarily responsible for King County's root wad and LWD installations is Mr. David Clark. Mr. Clark can be reached at (206) 296-8388. His addresses are: Rivers Section, King County Department of Natural Resources, 700 Fifth Ave. Suite 2200, Seattle, WA 98104, USA, or email firstname.lastname@example.org or click the following link: Mr. David Clark.
Q. Is more information available concerning LWD or root wad hazards?
A. Yes, you can email questions to the Webmaster of this site.
Q. Is anyone assembling information about the benefits or hazards of
rootwads or LWD?
A. Yes. A part of the purpose of this site is to gather information concerning the use of LWD, and make that available. Any information you have or your comments would be appreciated. You can email information to the Webmaster. If it is not possible to email it, please email a note describing the material and your address or phone number, and we will contact you.