Tuesday, November 6, 2012

November 2012 BMP Q&A

By: Todd Thomas, Water Resources Forester, Texas A&M Forest Service

Q: Just the other day, the topic of temporary stream crossings came up.  More specifically, how does TFS recommend that we cross streams and how should they be left after operations are complete on the site? 

A:  Excellent question, if you don’t give proper care and thought to your temporary stream crossings, many of the BMPs you have put into place on the tract can be negated.  A key component of any forest management activity is access.  In some cases you may not have to cross streams to access parts of a tract that you need to.  For instance, there may be another entrance or road that has been overlooked, a neighboring landowner may grant access through their property, or it may not be necessary at all once you have stepped back and looked at the bigger picture. 

More often than not, you are going to have to put in a stream crossing or two to get the job done, but remember to keep them to a minimum.  When selecting a location be sure and look for a straight, narrow section of stream with relatively low banks.  This will minimize the amount of disturbance to the stream and stream banks.  Higher banks result in a greater amount of disturbance than lower banks, and straight, narrow sections limit the amount of exposure the streambed receives from equipment.  Once you have selected the appropriate location, be sure that your approaches to the stream as well as the crossing itself is at a 90 degree angle to the stream, this ensures that as equipment crosses, the amount of the stream exposed to equipment is greatly reduced. 

Log skidder dragging logs across a temporary bridgemat
If the banks of the stream are too high for equipment to cross directly, a common approach is to lay slash bundles into the stream bed that can be driven across.  The only downside to this is that they must be removed following operations; this can take some effort and can result in a serious amount of disturbance.  However, this is a much better option than dirt crossings.  Dirt crossings should never be used and are never recommended.  Remember, the point of BMPs is to keep extra dirt from entering the streams, not to add any more.  One of the easiest alternatives for these types of crossings is to use bridgemats, otherwise known as skidder mats or dragline mats.  These mats are constructed of hardwood cants that have been bolted together and are extremely durable and can be used over and over again.  They can be laid in place with the grapples of the skidder and removed in the same fashion once you are done.  The best part is that you have stayed out of the stream bed completely and maximized water quality protection at your temporary stream crossing. 

Once it is time to move off site, temporary stream crossings should be removed and the approaches should be stabilized to reduce erosion.  One way to stabilize approaches is by revegetating them.  On page 65 of the most recent BMP handbook there are guidelines for revegetating disturbed areas, there is even a chart that gives you different seeding options so that you can use the best seed for your site.  Another alternative is to distribute fine slash down the approach (being sure not to put any in the stream bed) and drive over it to ensure firm placement, followed by larger, more coarse slash. 

In conclusion, remember to keep stream crossings to a minimum, always stabilize your approaches and to never use dirt crossings.   Keep the questions coming so we can shed some light on any best management practice confusion that might be out there, you can send your questions to me at tthomas@tfs.tamu.edu or just phone it in by calling (936) 639-8180.

*This article was published in the November 2012 issue of the Texas Logger

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