March 2013 BMP Q&A

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

Q:  I was looking at a Texas BMP compliance monitoring checklist and in the comments section, it mentioned “below grade roads”.  I have heard this term mentioned before, but I have never been quite sure what a below grade road is and what exactly can I do about them?

A: I am glad you asked this.  A road that is below grade is one that is lower than the surrounding land.  Many of the roads in East Texas are very old and can be classified as below grade. 

Below grade roads usually occur after years of being worked and graded without any new material brought in to build them up, or from just being worked from one direction, to the point that the road essentially becomes a channel for runoff water.  As you may remember, with BMPs we are trying to keep from channelizing any runoff.  When runoff is channeled it begins to accelerate, especially in areas with a great deal of topography.  This accelerated runoff will increase erosion and the amount of sediment that reaches our streams. 

The issue of below grade roads is not limited to areas with rolling terrain or steep topography, below grade roads can create significant problems in flatwoods as well.  The issue isn’t so much a concern with water quality, but with access.  Water will always flow to the lowest spot on a site, and if this happens to be the roadway, then the water will not properly drain.  The road will then become saturated, and stay wet for most of the year.  Wet roads can lead to poor access, and cause severe rutting if traveled. 

These situations can develop gradually over time if roads are not properly constructed or may occur when subjected to heavy rains.  The formation of these areas can also result from trying to access a wet road by cutting it down until a dry surface is reached.  While this might be a temporary solution to an access problem, it can lead to erosion problems. 

To fix or reduce the severity of these problems, the first thing you need to decide is if the road in question will function as a temporary or permanent road.  This can be dictated by the amount of traffic your road will handle in the near future.  High traffic zones will generally be more expensive to control than low traffic zones.   If the road is not necessary then it should be closed.  In order for the road to stay in use the surface will need to be built up and water control structures will need to be put into place.  The type of structure will be dictated by the traffic type.  

There are several effective ways to reduce the impact to water quality on below grade roads.  It is best to make sure that the roadway is well drained when dealing with permanent systems located on steep topography.  Installing waterbars with good outlets for the water is recommended.  Instead of using the dirt in the roadway to build these structures, try incorporating some of the bank dirt.  This will allow you to construct a waterbar and at the same time make it easier to divert the water. 

When dealing with temporary roads, revegetating is a great option to hold the soil in place and minimize the amount of erosion and sedimentation that may occur.  A more cost efficient way to hold temporary roads in place is to distribute fine slash on the roadbed.  If you have any questions about BMPs, please do not hesitate to contact me at (936) 639-8180 or email me at tthomas@tfs.tamu.edu.  

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