Friday, April 17, 2015

Spring 2015 BMP Q&A

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

Q: I have an old road that I use to access most of my property that is fairly steep in some parts and has high banks on either side.  The road itself has a good crown on it and sheds water well.  The problem lies with the ditches.  Due to the high banks I am unable to install any turnouts to give the side ditches some relief until the road reaches the bottom of the hill.  This makes for severely gutted out ditches.  What can I do to keep my ditches from being so washed out? 

A: Excellent question. Believe it or not, you are not alone in your problem.  This is especially common on roads that are retired county roads where years of grading left the road severely below grade.  Your issue is extremely problematic because if left untreated the erosion occurring in your ditches will eventually begin to undercut your road. 

The best option that comes to mind that would be the most long-lived would be the installation of small “Reno mattresses” in your ditches.  A Reno mattress is comprised of chicken wire, stakes (ideally rebar), wire ties and rock or other aggregate.  These installations should take up the full width of your ditch, be approximately one to two feet wide, and one to two feet tall.  The rock or rip rap you use should be bigger around than that holes in the chicken wire. 

Small Reno mattress installations in side ditch on steep grade
To install a Reno mattress, lay the chicken wire the width of your ditch, dump your aggregate on top of the wire to form a mound one to two feet wide and one to two feet tall, fold the wire over the top of your rock mound and use wire to tie the chicken wire shut.  Next, take your stakes and stake the Reno mattress down on the front and on the back.  When installing the Reno mattresses take care to ensure that any flow will not wash out the edges or undercut the installment.  To determine the number and spacing you will need, consult the Texas Forestry Best Management Practices Blue Book.  The chart for waterbar spacing on page 54 should suffice, however if you think you need more, go for it.  More of these will certainly not be detrimental.   

Top view of  Reno mattress
The functionality of these Reno mattresses is twofold.  The first function, as with all BMPs is to slow down the flow.  The second function occurs from the slowed down flow; once the flow in the ditch is slowed down any sediment it is carrying with it should settle out behind the installment.  Over time this should work to fill in the ditch behind the mattress while allowing water to pass on through.  Sort of a “filtering” effect. 

In closing, remember the primary functionality goals of BMPs, slow down flow to reduce erosion and to allow any sediment travelling with the flow to settle out.  Be sure to keep the questions coming.  You can call our office in Lufkin at any time, the number 936-639-8180, or you can email me at

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