September 2013 BMP Q&A

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

Q: My crew is in the middle of thinning a 15 year old pine plantation.  In the middle of the tract, leading down to an intermittent stream is an old legacy road that has washed out over time.  It is very apparent that the when all the timber was harvested over 15 years ago that no BMPs were used.  As this gully approaches the stream it gets deeper and deeper.  Where the gully meets the stream it is deep enough to swallow a pickup!  For the most part, the gully hasn’t eroded any more in quite some time.  There is little to no evidence of recent soil movement, and there is a pretty heavy layer of pine straw and other litter on top of the soil.  We have kept all our equipment out of the gully and haven’t cut any trees on the edge of the gully in order to keep things from washing out anymore than they already are.  What is our next move here?  How should we treat this highly eroded legacy road in future management operations? 

A: Excellent question, and one that addresses an issue that I am sure other folks are experiencing out there.  First and foremost, good job staying out of the gully and not harvesting the trees along the edge.  Even though the gully started out as a poorly placed road, it is now acting as an ephemeral drain and should be treated as such. 

The best way to keep this gully from eroding further is to keep equipment out entirely and to maintain a buffer of trees around the edge and above the head of the gully.  Now you may remember that Texas Forestry BMP guidelines do not require an SMZ on ephemeral drains, but depending on the situation, some protection is needed.  This is certainly a situation where some protection is needed.  The amount of protection, the width of the buffer, will depend on the soil type and topography of the site, based on your professional judgment. 

The buffer will accomplish several goals in the name of erosion prevention and protecting water quality.  The first goal is interception.  The canopy of the trees comprising the buffer will intercept rainfall and reduce the resulting soil movement from raindrop impact.  The second is root structure.  The roots of these trees will hold the soil in place, reducing the chance of the gully getting wider.  Since you are in the process of harvesting timber on site, the amount of water traveling to the gully is going to increase.  This surplus of water is a result of the harvested trees not being there to use it anymore.  The trees making up the buffer will intercept the bulk of this water, preventing further erosion. 

Maintaining a buffer also limits equipment intrusion.  Remember, since water is naturally draining towards the gully and in more abundance with less timber around to utilize it, the area around the gully is going to be much more prone to rutting.  Even in dry conditions it is important to minimize equipment operations immediately adjacent to the gully as this can cause soil disturbance that will eventually lead to further erosion issues. 

While it may seem like a good idea to place hay bales, slash, or silt fences in the gully, this should be avoided.  In a case such as this, where everything seems to have stabilized relatively well, putting something in the gully would likely cause further erosion on the side banks causing the gully to widen.  Placing hay bales or silt fences in the gully would not only enhance erosion, but also costs time and money.  Time and money that you could be devoting to other aspects of your operation, such as installing BMPs elsewhere!

In conclusion, an ephemeral drain is an ephemeral drain no matter how it started out.  No matter if a drain was put here by Mother Nature or the faults of man, at this point it deserves our protection.  Keep the questions coming, you can send them to me at tthomas@tfs.tamu.edu or call them in using the phone number 936-639-8180.  

*This article was published in the September 2013 edition of the Texas Logger