Texas Forestry BMPs - Locating Waterbars

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 tthomas@tfs.tamu.edu

August 2013 BMP Q&A

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

Mmmmm....dips. But not quite.

Q: While looking through the blue book, I noticed that you have specifications for both broad-based dips and rolling dips.  I was always under the impression that these were basically the same thing.  Can you explain the difference between the two, and when you might use one instead of the other?

A: Excellent question, and one that we get quite a bit!  Upon first glance, rolling dips and broad-based dips do not appear to be much different at all.  They both accomplish the same goal: to provide cross drainage on in-sloped roads.  The differences between the two are quite subtle, but knowing these differences can save you time and money down the road when it comes to road construction and maintenance. 

Both rolling dips and broad-based dips are reverse slopes in the road surface that outslopes for natural cross-drainage.  Rolling dips are designed to be used on haul roads and heavily used skid trails.  Broad-based dips differ in that they are designed for use mostly on heavily used haul roads.  Rolling dips can be used on roads with up to a 15% grade, while broad-based dips should be used on roads that do not exceed a 12% grade.  The spacing on broad-based dips should change with every 2% change in gradient, while the spacing with rolling dips changes with every 5% change in gradient. 

With broad-based dips, the reverse grade should always be 3% and approximately 20 feet in length.  Rolling dips are slightly more flexible in their size and gradient.  Guidelines for rolling dips call for the reverse grade to be between 3% and 8% with the length ranging from 10 to 15 feet.  The slight differences between the two allow for higher vehicle speeds on broad-based dips than on rolling dips. 

Since broad-based dips are used on high traffic roads, some other considerations may be necessary.  On some soils, the dip and reverse grade section may require bedding with crushed stone to avoid rutting the road surface.  Also, energy absorbers such as rip rap, and in some cases, a level area should be installed at the outfall of the dip in order to slow down runoff and keep erosion minimized. 

With both types of dips, neither the dip nor the hump should have a sharp, angular break, but instead should be rounded to allow smooth flow of traffic.  Properly constructed dips require minimal maintenance and continue to function years after abandonment, saving your road and saving you money. 

Please keep your questions coming.  You can email them to me at tthomas@tfs.tamu.edu or phone them in by calling (936)639-8180. 

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

What to consider: Culverts

Poorly installed and improperly designed culverts can lead to excessive erosion, damage to streams, high maintenance costs, and road failure.  In order to prevent these issues it is important to consider culvert type, diameter, length, and location.

Excessive sedimentation from a poorly planned culvert

Type
There are two types of culverts: stream crossings and cross drains.  The first type, a stream crossing culvert, is generally placed in a location where a permanent stream crossing may be necessary, since it is often too costly both economically and ecologically to remove. These culverts allow both stream flow and aquatic wildlife to pass underneath the road.  The second type, cross drains, are used to transport upland runoff, accumulated in road ditches on the upland side of the roadway to the lower end where both flow volume and velocity can be dissipated.

Mouth of a cross drain culvert

Diameter
Culvert diameter is determined by both the soil type on the site, how steep the site is, and the acreage of the watershed that the culvert drains.  Taking into consideration these factors ensures that the culvert is sizable enough to handle the maximum volume of water that it may encounter.

Culvert size chart from page 51 of the Texas Forestry Best Management Practices Handbook 

Length
Culvert length is dictated by how wide the road is.  Culverts should be long enough so that each end extends at least one foot beyond the edge of the fill on either side.

Location
Culvert location is paramount in dictating the longevity of the culvert.  In stream crossings, culverts should be placed in a section of stream where the channel is straight and the stream bed is firm.  Cross drain culverts should be spaced out depending on slope.  Cross drain culvert spacing can be determined using the following formula:

Culvert spacing = (400'/slope%)+100
         *Slope in percent is expressed as a whole number (i.e. 15%=15)
               
            Example: Spacing = (400'/15)+100'
                          Spacing= 127'

Conditions
In addition to factoring in culvert specifications, it is also extremely important to factor in current weather conditions and trends.  Culvert installation should be done when stream flows and chance of rain are low.  Ideally, the entire installation process should be completed before a rain event.

UP NEXT:  Installing your culvert

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

Crushed Concrete on the Jones State Forest

While more expensive than seeding, armoring a road surface with rock is an excellent way to prevent erosion and improve access, especially on roads that remain wet for long periods of time, experience heavy traffic, or are prone to erosion.  A popular rock to use is crushed concrete.  When structures such as roads and buildings that are made of concrete are demolished, it has become common practice to take this concrete and crush it for reuse.  After the concrete has been crushed, magnets remove any steel such as rebar that may be present.  The final product is a hard, granular aggregate that is composed of sand, gravel, and crushed stone. 

Crushed concrete is often cheaper than using natural rock aggregate since it is a byproduct of demolition.  Crushed concrete stabilizes relatively quickly once it is applied to the road creating a firm road surface.  Just as with using other rock material for roads, crushed concrete drains faster than if the road was left with its natural dirt surface, reducing the potential for rutting in the road. 

This week, 118 tons of crushed concrete was spread out on a section of road in the Jones State Forest in Conroe, Texas by TFS Resource Specialists Mike Adams and Ray Uballe.  The section of road where the crushed concrete was distributed is just one stop on the best management practices (BMP) tour down on the Jones.  The tour consists of various BMPs that have been put into application so visitors can not only learn about these BMPs, they can also see them in use. 



 Resource Specialist Ray Uballe spreads the crushed concrete following the delivery of the material

 


Resource Specialist Mike Adams smoothes the newly applied crushed concrete