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QUESTIONS and ANSWERS from webinar on Mountain Trail Sustainability

Webinar Follow up Questions & Answers, by Hugh Duffy, National Park Service

by Hugh Duffy, Landscape Architect and Project Manager, National Park Service

It is the first of a series of three on Sustainable Mountain Trails. Each webinar in this series is independent of each other and can be attended individually. Parts 2 and 3 will teach you to apply these principles to a trail network "One Trail at a Time, One Mile at a Time." The course includes Tools and Techniques, Examples, and Case Studies of mountain trail sustainability. These are responses to questions received during the webinar. A recording of this webinar, and Parts 2 and 3 are available through the American Trails Online Store.

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Q. Could you explain the 1/4 cross slope concept further?

Some background first. Per the Sketchbook and the Foundations webinar presentation, I recommend that the concept of mountain trail sustainability consider the Trail Project Cycle, from Assessment, through Planning, Design, Implementation and Maintenance. Recommendations in the Sketchbook (Guide to Sustainable Mountain Trails Sketchbook) are based on observations on the ground as well as practical experience with lack of maintenance, funding, etc., the so-called “7 Realities” on page 20 of the Foundations webinar presentation booklet. The Sketchbook also echoes the policies of the American Society of Landscape Architects, as well as the wilderness ethic of minimum intrusion on natural scenes established in the long tradition of federal land management agencies such as the U.S. Forest Service and National Park Service. Per the webinar presentation, the Sketchbook is a “What is ... & ... What can be ...” vignette.

Based upon the premise of getting water off of the trail as soon as possible as the key to minimizing erosion and its associated impacts, if a trail planner would pursue a trail corridor that goes straight uphill (fall line trail), water would have no chance to get off the trail. On the other hand, if a trail planner would recommend a trail that purely follows the contour, that trail would never climb, but logically water would flow across the trail from the uphill location and off the downhill side of the trail, minimizing erosion on the trail.

The 1/4 cross slope concept (recommended profile grades are less than 1/4 of the prevailing topographic cross slope) results in the most optimum range of profile grade versus cross slope for environmental sustainability. This concept fits the “narrow limits” espoused in the Olmsted Report of 1865 to preserve naturally occurring scenery, and to avoid construction markedly inharmonious with that scenery.

The 1/4 profile grade / cross slope concept is likely the paramount criteria influencing sustainability of backcountry mountain trail corridors while minimizing resource impacts. Historic trails literature commonly addresses recommended profile grades, average profile grade, and maximum profile grades. There are also two other popular concepts: “side hill” and “rolling contour” trail construction methods. These concepts are certainly viable techniques and potentially will result in sustainability, but the concepts themselves do not quantify the recommended profile grade relative to the prevailing cross slope. So, with all other factors and criteria being the same, the 1/4 profile grade / cross slope technique would allow steeper profile grades on steeper prevailing cross slopes.

It is prudent to give trail planners some tools to work with for their refinement on the ground. The 1/4 cross slope criteria addresses recommended profile grades (the relative rise of fall of a trail along the trail’s centerline) relative to the prevailing topographic cross slope (the larger topographic condition measured in the vicinity of the trail).

If a trail planner focuses on a desired profile grade without consideration to the prevailing cross slope condition, unacceptable impacts may occur. For instance, if a trail planner locates a trail with a profile grade of 10% on a prevailing cross slope of 20% (based solely upon a theoretical profile grade), then the trail will likely be more difficult to maintain, as well as potentially causing unacceptable resource impacts. A more sustainable approach would be to recommend a trail with a profile grade of 5% on the same 20% prevailing topographic cross slope. Some soil or topographic conditions and / or implementation solutions may be viable and sustainable at different relationships between the profile grade and the prevailing cross slope. The 1/4 cross slope criteria is a guideline only, whose goal is achieving the optimum condition for minimizing resource impacts and allowing for ease of maintenance, while minimizing the need for corridor re-routes.

In addition, the Sketchbook, pages 22 and 23, as well as page 78 explain this concept in additional detail. The Foundations webinar presentation booklet also displays additional graphics on page 14.

Q. What type of uses do you have in mind and would you see most of these principles and processes applying to other types of sustainable trails?

To edit the question slightly, my answer applies to trail use and trail uses, not trail users per se. There are different types of trail users when it comes to hiking use, for example. The design would be for the use, not what would be different types of users of the same trail use type. Inherent in a Recommended Design Solutions Hierarchy for Sustainability, see page 51 of the Sketchbook, would be accommodation of different user types, say of front-country, middle-country and back-country trails.

The concepts of mountain trail sustainability that were organized into the Sketchbook and related documents, focus on hiking, equestrian and mountain bicycle trail uses, with which I have experience. I am convinced that these three types of trail uses can be implemented successfully according to sustainability criteria with minimum environmental impact to resources. If I were to create a matrix of criteria for the different uses (er, which I have done), the primary difference between these three uses would be the inside radius of a switchback. I believe that the other criteria, from an environmental sustainability perspective, are very similar.

Yes, I believe that the principles and processes portrayed in the Sketchbook and related documents would apply to all trail types whose stated goal is to be environmentally sustainable. Criteria have to be established, environmental goals set, projects implemented, and then Lessons Learned summarized and applied to the next project. We all have to start somewhere!

Q. Are you familiar with these concepts being applied in urban settings?

I think you are referring to urban multiple-use / paved pathways. The Sketchbook generally applies to natural surface mountain trails.

Please note that I live in Lakewood, CO, a suburb of Denver. I live in the Green Mountain area, which has two large open space parks with many miles of trails, just 12 miles from downtown Denver. Almost all of the trails in these two parks are natural surface trails. Some trails, however, are paved multiple-use pathways which function as regional spine connections or commuter routes. And there are some mountain bicyclists who commute first on a paved multiple-use pathway, then over Green Mountain on a natural surface trail, then back to a paved multiple-use pathway to their destination, a good reason to live near such a valuable resource.

Please note also, that natural surface trails in urban settings would have to be more sensitively planned, designed and maintained, based upon their presumed higher volume of use many times during shoulder seasons (spring and fall) and inclement weather (muddy trail conditions or post-snowfall sunny days).
There are several conditions, similar to my location, in Colorado, including in Boulder, Colorado Springs and Fort Collins, and likely across the country.

Seemingly if a landscape architect were involved in a multiple-use pathway project in an urban setting, then yes, the same concepts would be applied in some fashion. Other trail professionals would use their own trail planning process. They may refer to their Tools & Techniques with different terms, but seemingly a plan would be developed according to some type of physical and geographic criteria, a design would be created and then the project would be implemented and eventually maintained.

I always recommend that a written and graphical Site Analysis be developed as part of deliverable packages for management and / or compliance review. An inventory of site features, and their implication for the suitability for a trail corridor via a Site Analysis is one of the unique Tools & Techniques advocated in the Sketchbook process. So yes, the concepts portrayed in the Sketchbook would apply to urban settings.

Q. What are some other good resources for costing trail projects?

That is a perennially great question! To directly answer your question, I would have to say that I have not found any.
There is a chart in the Sketchbook on page 54, for estimated Recommended Daily Requirements Per Mile of Trail Estimating Tool for accomplishments for natural surface trails based upon my experience. I always expect that if folks are seeing better or different production rates; that they could, like all of the Sketchbook Tools & Techniques, customize them for their project at hand. I have anecdotally heard that trail construction can cost $15,000 – $250,000 per mile or higher. The vast majority of my trails have been built by volunteers or day labor or youth corps, hence the basis of my labor estimates. Many agencies have daily rates or crew rates available and could be plugged into equations easily. Daily rates for laborers would likely be approximately $20 / hour average for natural surface trail projects. Assessment, planning and design costs could be extrapolated from the table on page 54 of the Sketchbook.
I periodically get phone calls asking how to do construction estimates for multiple-use pathway projects, for which I direct folks to Google and RS Means.

Q. Do you have any recommendations for monitoring strategies for levels of use on trails, such as trail counters?

No, I do not have recommendations for monitoring strategies for levels of use on trails. I have felt challenged to articulate to the trails community the physical criteria related to environmental sustainability of natural surface mountain trails. And it is a big challenge, and felt that that is where I could best serve the trails community over the years. Monitoring would be the purview of park management, to whom I am a consultant, even in the NPS (I do function this way internally to NPS parks).

My Sketchbook co-author John Giordanengo is a proponent of monitoring during Ecological Restoration activities, please refer to the Sketchbook.

I include a summary of trail monitoring activity recommendations in general form on page 127 of the Sketchbook. What is shown there is an excerpt from NPS Natural Resource Management Reference Manual # 77, 2006. Theoretically, NPS trail managers are aware of the monitoring concept and are implementing some kind of monitoring strategy to help manage their backcountry trail programs. Any actions are up to their unit management.

Q. What triggers the need for re-routing a trail rather than maintaining it? In other words, when do you know that maintenance is simply not going to cut it and that you must give up and essentially “start over”?

This is one of the hardest questions I have ever had to answer myself. It is a giant responsibility to come to such a recommendation, and eventually, to make such a decision. Ultimately, it will be a decision documented in a compliance process, and likely made by your unit manager.

Please consider the Sketchbook hierarchy of Maintenance / Rehabilitation / Armor Strategies as shown on page 126. Per the philosophy of the Sketchbook, some Armor will always be required and a combination of Maintenance (even several times per year) and Rehabilitation are always presumed, not just simply Maintenance Strategies.

From page 136 of the Sketchbook: “Many times, the hardest decision agency managers have to decide is whether or not to continue to use existing corridors, maintain them, rehabilitate them, or abandon them [with ecological restoration of the old corridor] and start over with a new trail design according to sustainability criteria. Once a decision has been made, incremental and patient actions which are part of the overall design plan will result in the most beneficial project regarding natural and cultural resources protection, land management agency goals and stakeholder interests.”

We didn’t talk much in the Foundations webinar about conducting a Trail Sustainability Assessment. I mentioned the term, plus I mentioned it when referring to the Trail Project Cycle Tool. I also mentioned using the New Trail Design Notes Tools “backwards” through the Trail Planning and Trail Sustainability Assessment processes. By this I mean that it is prudent to understand problems and solve them through design, and if trail planners are to do this successfully, they must assess and plan appropriately for their design.

Pages 27 through 32 in the Sketchbook include my recommendations for Tools & Techniques for a Trail Sustainability Assessment process which I will discuss on webinars 2 and 3, and give examples from my experiences. In particular, I believe one must assess trails for sustainability according to appropriate trail sustainability criteria. These are suggested on page 29 of the Sketchbook. Determining if a trail leaves at the appropriate origin, connects appropriate control points (intermediary linkages), and arrives at appropriate destinations; while also traversing appropriate cross slopes at appropriate profile grades, are foundational to a Sustainability Assessment. Having the Sustainability Assessment in written, graphic, photographic, and tabular form will strengthen your presentation.

Page 31 of the Sketchbook says this:

“Prevailing cross slope and trail profile grade readings taken with a clinometer, while also recording additional sustainability notes, will assist the interdisciplinary trail team in assessing trail corridors or surfaces for planned activities. Readings are recommended for each 100-foot station.

"The higher the percentages of unsustainable soils, excessive cross slopes or steep trail profile grades, the more likely it is the corridor should be simply maintained, rehabilitated, armored or relocated to more sustainable sites. If over 50% of a corridor is unsustainable, it is likely that the entire corridor needs to be abandoned, restored, and then a new corridor relocated to better soils or prevailing cross slope locations. Armor improvements (sometimes just minor spot improvements) will almost always be required to keep a trail corridor and travel surface in sustainable condition.”

I wish I had a better answer, but I have made recommendations to abandon, ecologically restore, and then create new corridors for 25 miles of trail— several times.

I would recommend that your team make recommendations based upon each corridor’s uniqueness, on how to proceed, and not go by the 50% number above carte blanche. So, how is the corridor doing, relative to profile grades, prevailing cross slopes, origins, destinations and linkages, etc.? I could picture some scenarios where half of the corridor is unsustainable, you might make a decision to start over, and others where maybe because of resource concerns or topographic constraints, you might continually improve a corridor through Rehabilitation and even Armor solutions even if the corridor is largely unsustainable. I would recommend you convene an interdisciplinary team with trail sustainability experience. And please note, a continuously armored trail corridor or trail segment of a corridor, may be the most environmentally sustainable option.

I mentioned during the webinar, the June 2014 American Trails e-newsletter that referenced a proposal headed to Congress to fund maintenance backlog activities on our nation’s federal trail system to the tune of several hundred million dollars. I don’t know what the outcome of that initiative will be, but I do know that each of us has to double up and recommit ourselves to working hard and ensuring we are doing our absolute best to start now to reduce what will an increasing backlog if we don’t take the correct actions now. If not us, who?

Hence the subtitle of my Foundations webinar presentation: “One Trail at a Time, One Mile at a Time.” I think it would be noteworthy for a trail manager to endeavor to restore to sustainable condition a single 5-mile-long corridor, one mile per year say for 5 years, rather than continue to hamstring future managers, by say, creating 5 miles of unsustainable trail in a single year, just to make some kind of mileage accomplishment.

In a nutshell, I would recommend that you make your best recommendations to management, conduct a transparent compliance process, and follow that with hard work.

And, alas, if you look at the Sketchbook, 2007 edition, on page 19, I recommend starting with the Trail Sustainability Assessment (that was in 2007!). My trail friends have since recommended that an interdisciplinary team start with “Pitfalls to Avoid” as indicated on page 35 from the Foundations webinar presentation booklet, which makes some sense, work through Lessons Learned and conduct More Tools research, then proceed to a Trail Sustainability Assessment, then Plan, then Design. Yikes! They might be right. I might want to edit the Sketchbook. So there might be Lessons Learned and Pitfalls to Avoid that you might tabulate first, even before venturing afield, and include those in your Sustainability Assessment.

Q. What if you have a great viewpoint, but it is very steep and virtually impossible to design a curvilinear alignment to get to it and one switchback won’t get you there? My users want to get there, and we want to accommodate their interests. How would you approach this challenge?

I hear you loud and clear! This is very common challenge in Colorado, and the Eagle Cliff Case Study that I showed you in the webinar presentation demonstrates this reality.
Think of the concept of sustainable mountain trails this way: the overwhelming preference would be for a natural surface, curvilinear alignment (rolling contour, side-hill or 1/4 profile to prevailing cross slope conditions) with gentle to moderate profile grades on gentle to moderate prevailing cross slopes— with required spot (a.k.a.: armor) improvements. I strive to achieve a sustainable trail corridor which would be about 85% of its length as natural surface, and 15% would be armor improvements which may include walls, switchbacks, stone paving, imported gravel surfacing, extensive drainage improvements, crowned trail, bridges, etc. So for a mile of trail, there might be 500 to 750 linear feet of atypical trail constructed. < This is reality, and my targeted percentages might be low for some projects. Maybe a project goal would be to achieve only 50% natural surface and 50% of its length as some kind of armoring.

Now take this a step further, to your question. There is a term in Colorado which refers to the concept of “switchback trails” to Colorado’s high peaks (we call them “14ers,” as they are over 14,000 feet in elevation). Eventually— even if you can find a sustainable corridor starting at say 11,000 or 12,000 feet of elevation— you will face the reality of having to navigate rock outcrops, talus slopes, scree and mountain tops (which have resisted glaciers). Hence the term: switchback trails. Trail planners have had to do the best they can with the lower elevation routes, and then plan, design and implement extensive sections— of what is referred to in the Sketchbook— as Ascent Routes. See page 130 of the Sketchbook for Armor Design and page 140 for Colorado Fourteeners Initiative Ascent Route Samples. This also would apply to lower peaks that are challenging topographically.

See also page 121 of the Sketchbook for inspiration for Stone Craftsmanship examples Rocky Mountain National Park. Many times for the 14ers, this results in switchbacks to the top, many times over several hundred feet of vertical climb.

All of this pinpoints the need to thoroughly plan the lower segments of such a route to what would be the Ascent Route origin— a.k.a.: “switchback trail” route— to the desired destination. The next step would be to then consciously design (and get funding and work out the logistics for) the final higher-elevation segments, hopefully in their ultimately best location the first time. Truthfully, five or ten switchbacks don’t sound so bad to me. There are Trail Management Options shown on page 133 of the Sketchbook which you may employ. GIS and GPS technology can help you figure the rise and run you have to navigate, and their geographic relationships.

And I believe that properly planned, designed and implemented switchbacks will not be shortcut as many presume and as often as they presume. I believe trail users are, for the most part, ethical. Some signage or informational brochures are always helpful. I think you are up to the challenge, just by your sincerity in asking the question. Yes, your trail won’t be typical natural surface trail throughout its length, but the alignments you choose and the stone craftsmanship for the upper stretches will likely be an inspiration to your trail users.

Q. You recognized that funding is scarce. We have found that it is easier to find money to construct a new trail, but funding for relocating or maintaining trails seem to be hard to come by. Do you have any ideas for us?

I am going to answer this question similar to how I did on the webinar. I believe if you put all of your ducks in a row, and develop a comprehensive package which would communicate to funding authorities what you intend to do as well as why you intend to do what you plan to do and how— that you have given that effort your best shot. I believe that that comprehensive package would be based upon sustainability and in a “soup to nuts” format, i.e.: assessment, plan, design, maintenance— customized to your project.

I understand that funding new trails might be desirable to a funding authority versus maintenance. But if that would be done— not to sustainability criteria— what have you or they gained?

I recommend that you put together the Comprehensive Trail Sustainability package and stand firm in your commitment, and confidently ask just like any other request you might have in the real world, cookie sales, youth group trips, band trips out of state, or whatever. I think you will be successful.

Q. For a backcountry trail, what type of material might you use to make it more accessible— if you don’t want to pave it?

Paving in the “backcountry” would probably be problematic, I agree. I am aware of projects where remnant paving in the backcountry is being removed at great cost. And I presume you are talking about literally improving a trail for better access for users, but not making it recreation accessible according to the new Guidelines for Outdoor Recreation Facilities on Federal lands. Note that you may have to comply with those guidelines depending upon your specific circumstances.

To improve trails for better access, I commonly recommend a local crushed-gravel mixture, similar to a road base specification from a highway department. This might be something like a standard specification “3/4-inch minus” mix, say xx% passes a 3/4-inch sieve, yy% might pass a 1/2-inch sieve, zz% might pass a 3/8-inch sieve, etc. I always recommend incorporation of some fines, but not a large percentage.

It would be best if a landscape architect collaborated with a civil engineer and a gravel operator to produce and test several mixes and then pick the best and proceed. In the backcountry this recommendation could be a challenge. Maybe geotextile fabrics could be employed to reduce the cross section of your needed gravel and therefore the needed volume. Maybe you could source the materials, have them delivered to your trailhead and then transport them to your location. I don’t know if this feasible for you or not. I am aware of locations where gravels are even sourced in the backcountry and mixed and utilized. It is a small challenge but it has been surmounted in the past.

Q. We have a park with 50+ miles of multiple-use trails. They cross in many places. Would you recommend signing every single intersection with a number and posted trail map? Is there a reference book or article that explains the best process for signing/numbering such a complex trail system?

I have not seen a reference document that would specifically address this question. Suzanne Trapp authored a very good book entitled Signs, Trails and Wayside Exhibits. See the Sketchbook page 151 in the More Tools section. I act like a novice many times when visiting new areas, and I get confused many times. I think, yes, it is prudent to minimally sign trail intersections for way-finding success. I would recommend simplicity, and not necessarily a map as you allude to, at each intersection. Simple trail names, and directional arrows and maybe distances work in many places. There are products advertised in the American Trails Business Directory that are suitable for your solution.

Q. Tom Crimmins ("Management Guidelines for OHV Recreation") suggests the "50% rule" for OHV trail cross slope. "Trail grade should never exceed 50% of the cross slope of the area being crossed." Is this the same concept as the 1/4 [profile versus prevailing topographic] cross slope you suggest? Are OHV designs and hiking designs different in this area of design?

The 1937 NPS CCC-era training document, which I alluded to on the call, is now linked on the NPS Sustainable Trails website. The CCC-era training document starts with an admonition, and that is that document is not a set of standards, and that the technician in the field must make decisions on the ground.

I was trained this way in the old days by previous NPS trail planners, that “there are no rules.” I continue to espouse that philosophy— that there are no rules.

The Sketchbook is written as a motivational document, and it is a guideline only. That philosophy conveys responsibility to the interdisciplinary team to customize recommended Tools & Techniques to their project at hand based upon sound judgment. The Sketchbook and related documents are clearly focused on criteria that influence environmental sustainability of natural surface mountain trails, as recommended by the authors. A simple example is from the Foundations webinar presentation booklet on page 14: “The most sustainable corridor location from any given point would be left or right, 1/4 uphill or 1/4 downhill.” This is accompanied by a graphic. Please refer to this page of the presentation.

There is scientific literature on the web that confirms that trails that climb or descend at less than 1/4 of the prevailing topographic cross slope exhibit less erosion than trails that climb or descend at steeper grade relationships. See also the Minimizing Resource Impacts, 2012 document.

The Sketchbook advocates environmentally sustainable Tools & Techniques that— when customized— work in most situations most of the time for natural surface mountain trails. This is the prudent approach when publishing guidelines for others to contemplate.

I recommend that trail planners assemble their own library of resources and make their own assessment as to applicability of recommended sustainability criteria to their project at hand based upon their project’s requirements and the project’s stated environmental goals.

The Sketchbook, complete with its environmentally sustainable Tools & Techniques can certainly be a resource— and customized for the project at hand— in any trail planners’ More Tools library. The Sketchbook process can be successfully applied to all trail types.

Published June 2014

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