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02.16.12Gregory Ray

Capturing California’s Most Elusive Visitor

DG trail with water damage due to poor design and/or maintenance DG trailDG trail as environmentally friendly community amenity

The number one reason we don’t we use permeable walkways and trails more throughout our communities –  potential for water damage.

Letting Water Slip Through the Cracks

A large part of why we have no water in southern California is we don’t capture and store it when we do have it. Paving the land with impervious surfaces (roadways, sidewalks, etc.) is the primary reason we don’t have the ability to store rain water efficiently. Part of the answer is to pave more areas with more permeable surfaces. However, there are challenges in doing this and we need to understand those challenges and address them through quality design.

Decomposed granite (DG) trails are a great solution. The product of the weathering of granitic parent rock material, DG, is a granular, compatible soil type that is commonly used for paths and other paved surfaces. Decomposed granite is much more permeable than conventional paving materials and can usually be installed at a much lower cost. Its permeable nature allows water percolate down through the granite, reducing runoff problems and allowing moisture to reach underground roots from nearby trees and shrubs. But, if not designed and installed correctly, the positive qualities can quickly be overshadowed by negatives.

Don’t Run Off…Stay for Awhile

DG trails are a great addition to any rural community for many reasons including:

  1. Soft paving for aerobic jogging or walking
  2. Great surface for equestrian
  3. Reduced heat island effect (reflective heat)
  4. Blending better into a natural setting

In many studies throughout the country, walkers, bikers, and equestrians ask communities for natural surfaces to enjoy.  Begin the trail with the disabled in mind and continue that access throughout.  Discover if there are any interesting places or other trails to connect to. Figure out if this trail will be for transportation (kids getting to school), recreation, or both.

The intended benefit of the DG path throughout the community is to give residents an amenity within their community that can be utilized by all.  The added benefit is that this amenity allows the community to give back to their own surrounding environment.

When Water Trips You Up

DG trails sounds like a win-win right? So, why isn’t DG more commonly used?

Water damage or erosion on trails is the number one reason. Water damage can create unsightly erosion and unsafe deep trenches exposing tripping hazards. This is typically caused by poor initial trail design, which can rarely be overcome, even by regular maintenance. Another cause is inadequate or inappropriate maintenance, which can both increase trail problems and wastes valuable crew time.

Trail construction and maintenance is an inexact science with many variables. Much depends on the location of the trail, the soil, the climate, and the types of uses. However, there are certain general guidelines which, if adhered to, will prevent most trail deterioration and minimize maintenance costs. Here are some design rules to follow when using DG for your community’s trail system.

Rules of a Crack-Free Road

  1. Get the high water flows from heavy storm events into vegetated areas where the water has more time to percolate.
  2. Pay attention to the gradient. Highly erosive, sandy soil requires a flatter surface, so even a 5% gradient could be too steep. Granitic soils are more forgiving and therefore can hand up to a 15% gradient, but keep in mind trails less than 10% are far more comfortable to hike and ride.
  3. DG requires stabilization, which is a very specific treatment during installation including scarifying the DG material, applying top coats (understanding when and how many to apply based on how the DG responds) and knowing when to compact the DG. Make sure to work with someone who has experience with this material before proceeding.
  4. Install and maintain water bars to divert water off a trail at controlled points along the trail. They can be incorporated in the original construction of a trail, or they can be installed later as a maintenance measure. Done well, a series of water bars can effectively eliminate erosion and stabilize a trail for years. Done poorly, water bars can accentuate trail erosion and become dangerous tripping hazards.

 

Ultimately, the most influential component of trail maintenance is the original trail design, alignment and installation. A well-designed trail will be easier to maintain, will deteriorate more slowly and will be more pleasant to use.

On the other hand, a poorly-designed trail is difficult to maintain, deteriorates quickly and, once you lose it, there’s not much that can be done to restore it. In addition, a poorly designed trail will always be less pleasant to hike or ride.  Shown in the accompanying photos is a comparison of a well-designed trail versus one which has design flaws that allowed erosion.

Just the same, if a well-designed trail isn’t maintained properly, your trail will still suffer from many of the common problems that occur with DG.

Keep a look out for my next blog post on DG, which will focus on my recommendations for properly maintaining your DG trails. In the meantime, please feel free to share your experience using and working with DG and any design tips you believe should be added to the mix.

Also, next Wed, Feb 22 at 2PM ET/11AM PT, I will be discussing permeable surfaces and DG live on Twitter. Follow and join the conversation by tuning into #landscapechat.

Greg Ray


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Gregory Ray

What do you call a landscape architect who understands how to design memorable environments that are also constructible and highly functional spaces? The answer is Gregory Ray. Greg recently came to ValleyCrest from the home building industry where he led the landscape program for a major home builder. Prior to earning his degree as a landscape architect, Greg founded a landscape construction company to earn his way through college. With over 30 years of experience, Greg has found his passion in reintroducing an attractive native plant palette in drought prone communities throughout the Southwest and Western regions.

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COMMENTS (6)

  1. Friday, 4:10 Puy Alonso Martínez

    The topic is very interesting and applicable here in Spain, where this type of trail is very common and easily found in poor condition.

    I would like more information on what methods you use to stabilize DG across the Atlantic. Are there any guidelines or technical recommendations in this regard that are applicable?

    thanks

  2. Friday, 4:26 Bill Curtis

    First, the stablizer for DG costs more than the DG. Secondly, if the stablizer is not applied correctly it is utterly worthless as it won’t serve the purpose and contractor’s are infamous for cutting corner’s and using concrete rather than stablizer and even then mis-apply that material. The result of mis-application of these materials ends in DG pathways being erroded by flooding. Next, of course is collection of water that has infiltrated thru the DG, which bring a plethora of other reasons why trying to convert path’s in to water collection points a very bad idea. For instance, even if the water did percolate thru the DG the soil under the DG will be eroded by the water, which will cause the DG to lose stability, crack and collaspe eventually. I’m sure a way can be divised to accomplish water harvesting from rain run off, but to attemp this from DG pathways would be so expensive that in my opinion this is idea isn’t going to get off the launching pad and better off forgotten!

  3. Friday, 5:15 Phil Bednarek

    This holds true for central sewage plants as well. With decentralized collection and redistribution back into the community where it was generated keeps the water local. Sending water/sewer miles away cost more and is busting many government budgets now. Newer developements need to incorporate local water and sewer mini plants to control cost and keep replenishment of their supply forever.

  4. Friday, 7:50 Gregory Ray

    Here is a quick guildline for the installation of a product called Technisiol G3 Stabilizer. More info can be had by contacting Sean at sean@technisiol.com.
    Please note that the product is not needed on the entire trail. See Blog photos!

    Topical Installation of Technisoil stailizer
    1. Scarify DG material to 1.5″-2″ depth. This machine is handy -Rotadarion STH 36 or larger model http://www.youtube.com/watch?v=DcK-jpZPbsQ
    This unit is handy to also till polymer into existing pathway after first two coats.
    2. Apply two top coats at 20 sq. ft. per gallon and then 30 sq. ft. per gallon. The second coat should take longer to absorb. If the second goes in quickly the path could take a third base coat.
    3. Compaction – Wait for optimum moisture content prior to compaction. After first and second coats you want to wait for the polymer to disburse through the DG. This can take an hour plus or minus 30 minutes either way before the material will be 7-8% moisture content. This is a typical optimum moisture content for optimum compaction. You want to compact to 95%. A simple rule would be when you compact if you see mud skidding it is too wet, and wait. If it compacts and get very tight this is optimum.
    4. Let the whole area dry. This could be 1 day to 7 days depending on weather and wind. You will probably experience a 2-3 day dry time.
    5. Top coat
    Maintenance Recommendation for City
    1. A general rule of thumb will be 2-3 years in low traffic areas and every 1-2 years in higher traffic areas. A singe or double top coat will be sufficient at 30-40 sq. ft. per gallon.

  5. Friday, 8:27 David

    I’ve used stabilized d.g. in my designs and I like it for a number of reasons-but permeability isn’t one of them. Stabilized d.g. is not very permeable-it’s almost like asphalt. Plus in clay soil if it was permeable you might need a subdrain anyway.

  6. Friday, 8:45 Gregory Ray

    The Technisiol stabilizer is less permeable but PLEASE NOTE that the areas in red on the blog photos are the only areas that get the Technisoil stabilizer. There is an additional organic additive used in the DG that helps keep it from eroding called Natracil from Gail Materials 951-667-6106. This product is permeable and comes pre mixed from the plant.

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