The purpose of this paper is to share information with field personnel. It provides information on an innovative temporary stream crossing used on a timber sale in Region 9. Information was provided by Charlotte Bofinger on the Ottawa National Forest. Other approaches are also included. San Dimas Technology and Development Center (SDTDC) did not have the opportunity to evaluate these temporary structures in the field. The structures described worked for the people providing the information. Local conditions should be carefully evaluated to determine if one of these structures will work in other areas.
Region 9 Structure
The situation was a summer drainage crossing for a forwarder. After installation the crossing got heavy use for a month or more and then was removed. The stream course was running water to a depth of 12 inches and up to three feet wide. The crossing was created using a separator material, a corrugated plastic pipe, and pulpwood. The separator material keeps the logs from being pushed into the soil and results in cleaner logs being hauled out of the woods. A pervious, non-woven geotextile is recommended. After the crossing was no longer needed the pulpwood was removed and hauled. The separator material and pipe were removed for reuse.
The above pictures show the temporary crossing in place and after its removal.
Above: Close-up of channel with separator material, pipe and pulpwood.
Below: Close-up of channel after removal of the temporary crossing. Note the indentations of the logs. Ground cover of organic material is still in place after the logs are removed.
There are several things to consider before installing a temporary crossing. These may vary by location, slope, local weather conditions, season of use, etc.
- Expected stream flows within the period of use. This will influence the pipe size.
- Wildlife/Fishery habitat disturbance. Are there threatened, endangered or sensitive species or their habitat present? Does stream provide habitat for aquatic or semi-aquatic species? These questions should have been considered during the environmental analysis phase of the project and documented in the Environmental Assessment (EA).
- Structural integrity of the crossing. Consultation with a transportation planner or engineer is recommended to make sure materials used will meet the needs of the structure and equipment crossing it.
- Soils/hydrological concerns. Subsurface flows, likelihood of slumping, erosion potential, etc. should be considered. This is particularly important on steeper slopes or with an incised channel. These concerns may also have been addressed during the environmental analysis phase but may not be site specific enough to cover this small of an area. If not documented in the EA additional analysis is necessary before implementation.
- To prevent the pipe from being crushed and blocking flow it is necessary to have enough logs over the pipe to disperse the weight. This depends on the size of logs being used. The logs also need to be placed carefully (tightly) to prevent shifting which could cause the pipe to be crushed.
- It is necessary to get documented agreement from the timber purchaser as to standards for installation, recovery of the logs used, and timely removal (seasonal or weather related) of the crossing. It is possible to get substantial channel scour if storm flows move the logs. Agreements should include provisions to remove the logs if heavy storms are predicted where flows may exceed the maximum expected.
The following information was provided following a request from SDTDC for additional information on temporary crossings similar to the one on the Ottawa.
An example of a crossing in Region 5 was shared by Tony Rodarte on the Tahoe National Forest. The crossing had already been removed, therefore only "after" pictures are available.
The situation was an ephemeral drainage used during August when the chance of measurable precipitation is minimal. The crossing was removed by September 15th. The need for a temporary crossing was recognized during the NEPA process and was included in the analysis. There was no pipe or separator material used. The harvest was a whole tree thinning from below. Whole trees (10 to 24 inch dbh) were used in the drainage. The material used was included material under the contract. After the crossing was no longer needed the material was removed with a heelboom loader and processed at the landing. Standard erosion control measures were required. The material was required to be removed after use and before expectation of rains (a date was specified). Straw was required to be placed at the crossing above the apparent high water mark on both sides of the channel. Some breakage of limbs and tops was experienced but all slash was removed from the drainage. The end result can be seen in the pictures below. Water evident in the pictures is from a November rain 2 or 3 days before the pictures were taken. The rain event was almost 3 inches.
Another innovative approach was shared by Ken Heffner in Region 4. This has been used in the past but no pictures are available. This approach involves laying chain link over the stream course with a chain attached to one end. The chain link is covered with logging slash/limbs. Mineral soil can be placed on top of the logging slash to create a running surface or snow can be used in the winter. The crossing is removed by using the chain on the opposite stream bank and pulling with a skidder or other equipment and rolling the whole thing back towards the near side of the stream. The chain link, slash, and earth/snow all come out like a "chain link burrito" and the original channel isn't disturbed at all.