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Trail design and construction

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This excerpt from "Pathways to Trail Building" is a concise introduction to the essential skills that lead to good trail design and appropriate trail layout.

arrow Tennessee received the Outstanding State Recreational Trails Advisory Committee award for 2010 from the Coalition for Recreational Trails.

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Basic elements of trail design and trail layout

From

The goal of trail building is to create a long-term relationship between humans and nature. This is only possible through a clear understanding of the needs of each trail related agency laced with a healthy dose of day-to-day reality. Planning and responsibility are the keys to success. Learning how to build a trail is an ongoing, never ending process with each section of trail to be constructed a new challenge. The trail designer/constructor learns over time the nuances of the forest, rocks and streams and how important it is to build a sustainable trail that is easy to maintain and becomes a natural part of the landscape. Sustainable trails minimize environmental impacts, are easy to travel and reduce future trail operation and maintenance costs..

photo of people digging trail

Trail building in Beaman Park, Nashville, TN (photo by Del Truitt )


Trail Design

Trail design is one of the most important factors to insure that the route offers optimum scenic, geologic, historic, cultural and biological sites to provide a variety of diverse habitats for the trail user to experience. Trail design is the critical connection to make the trail sustainable, to reduce impacts to the natural environment, and to minimize future trail maintenance.

Sustainability

The National Park Service definition of a sustainable trail is:
• Supports current and future use with minimal impact to the area’s natural systems.
• Produces negligible soil loss or movement while allowing vegetation to inhabit the area.
• Recognizes that pruning or removal of certain plants may be necessary for proper trail construction and maintenance.
• Does not adversely affect the area’s wildlife.
• Accommodates existing use while allowing only appropriate future use.
• Requires little rerouting and minimal trail maintenance.
-- From the National Park Service, Rocky Mountain Region, January 1991

The trail planner should consider the following features for inclusion.

1. Ridge lines: Ridgelines offer prime opportunities to avoid the high cost of trail construction with steep grades on side slopes. Ridgelines also can provide panoramic views of the surrounding countryside.

2. Bluffs and Cliffs: These steep sided gorge edges offer trail routes with few construction problems except for where large streams cut through the bluff edge. High cliffs, deep ravines and rock outcrops covered with lichens and mosses offer attractive vistas along the trail route. Main trail routes should stay away from the edge of the cliffs with an occasional short side trail to an overlook location. Overlooks should be at one–half mile to one-mile intervals if a good view is available without having to cut any trees.

3. Stream Bottoms: Streams offer both opportunities and challenges. The additional moisture in riparian environments creates conditions suitable for many plants and wildlife species not found in the surrounding upland areas. These high moisture conditions can make the trail tread muddy and will generally require the placement of stepping-stones or raising the trail tread with boardwalk structures. Trails in stream bottoms should avoid thick vegetation areas such as canebrakes, saw briar and grapevine thickets.

Areas of wet or poorly drained soils also should be avoided. Advantage should be taken of any natural “benches” or terraces running along the bottoms of a gorge that may be adjacent to a stream.

4. Points of Interest: A well-designed trail should include as many points of interest as practical and feasible along the length of the trail. Some points of interest may include:

• Geologic features such a bluffs of sandstone or limestone
• Hydrological features such as ponds or lakes
• Cascades or waterfalls
• Historic and cultural features
• Large or interesting trees

If potential overuse of these sites is an issue, routing the main trail away from the feature and providing access with a spur trail will reduce the amount of impact to these points of interest.

Areas to Avoid: Some problem areas to avoid include:

• Active farmland
• Old home sites with wells or cisterns
• Construction problem areas that include very rocky or steep slopes
• Wetlands or swampy areas
• Areas of exotic invasive vegetation such as privet or multiflora rose thickets
• Stay at least 25’ from the edge of a stream to prevent impacting the resource
• Property boundaries – stay 100 feet away from adjacent landowners if possible

 

Trail Layout

This section deals with the equipment needed and procedures for selecting, marking and identifying the trail route in the field. Trail sustainability is the primary goal of trail layout with ease of construction as a secondary goal. If constructed properly, trail tread stability can be maintained indefinitely, even over steep slopes and rocky areas.

1. Materials and instruments:

a. Plastic surveyors tape - Different colors (orange, red, blue and white) are useful for trail marking purposes. Use the blue to mark the main trail, red to mark control points such as road/trail junctions or stream crossings and orange for points of interest such as overlooks, waterfalls or unique natural features. Carry a black permanent marker to write notes on the tape if needed. This type of tape can be found in some hardware stores and can be ordered from companies like Forestry Suppliers, Ben Meadows, etc. Check the picture on the front cover to note the white flag between the 2nd and 3rd trail workers.

A recommended method of marking the trail route with flagging tape is to wrap the tape around the tree twice and tie the knot on the side of the tree the trail will pass. Leave a tail (piece of flagging tape 12-18” long) to help identify the knot. Whatever method to mark the trail is chosen, be consistent, so there are no questions where the trail route is located and tread construction is to take place.

b. A compass is still a useful tool to guide the trail planner for topo map orientation and to find control points and determine which ridges or stream valleys to follow.

c. A clinometer with a percent scale is used to determine the percent grade ascending (positive) or descending (negative) as the trail route is marked.

d. A 25-foot tape measure is used to determine trail corridor width and to calculate tread width on graded trails.

 

2. Field Reconnaissance:

Maps and other equipment are only tools to assist in the on site visit to a potential trail location. Exploring the area through which the trail is to be routed is very important and needs to be done several times before selecting the preliminary route. Important items to concentrate on when exploring the area include the following:

a. Points of interest – Interesting features may be identified on the map and located by on-site inspection. Draw in the additional interesting features that are not on the map.

b. Stream Crossings - Stream and road crossing(s) need to be researched thoroughly due to the potential dangers and importance of these points on the trail route. Streams are subject to water fluctuations sometimes as much as 5-10 feet or more and a bridge may be necessary to cross a creek. Extensive scouting to find the best location for the bridge site is very important and the lowest part of the bridge should be 5-10 feet above the highest flood level. The managing agency must approve any bridge design that would be built on the trail.

c. Road Crossings - Careful location of is very important. Visibility on road crossings with heavy traffic should be a minimum of 500 feet in both directions. Check with the managing agencies or the state Department of Transportation when considering a road crossing.

d. Level areas - Since long straight trails are not aesthetically pleasing, design slight right and left curves into the trails to avoid a highway effect. Sight distance should be 50-100 feet ahead of the trail user.

e. Steep hillsides - Steep areas present situations where careful trail location and design is essential. When possible, avoid locating trail routes on steep slopes. However, where soils are deep and side slopes are not excessive (greater than 25%), few problems are likely to occur on well-designed and constructed trails.


3. Techniques of Trail Layout:

Conditions from level to steep will affect the way a trail route is determined. Side slopes of 0 - 5 % do not require side hill construction. Side slopes over 5% need side hill construction know as “trail grading” (see section 3.b.). General techniques for trail layout are as follows:

a. Level Terrain (non-graded trail sections):

• Avoid long straight sections of trail. Long meandering right and left curves and changes in direction will help alleviate trail monotony.
• Avoid obstacles such as trees greater than 3 inches in diameter, areas with numerous dead trees, wet or low lying areas and areas infested with exotic species such as privet, bush honeysuckle, kudzu, multiflora rose, etc.
• Route the trail near interesting or unusually large trees, patches of wildflowers, rock formations and water sources such as springs and small creeks.
• When approaching cliffs or bluffs, do not directly route the trail along the edge of the bluff. Instead, route the trail 50-100 feet back away from the edge, and extend a short spur trail to a scenic overlook area. Overlook areas should be naturally open to minimize the need for cutting of trees or pruning branches to get a view. Signs at the trail junction should warn the trail user of the high bluffs and a warning sign should be located at the overlook.
• Do not route the trail along old roadbeds or jeep trails except where they are impassable to motor vehicles.
• Instead of following the ridge crest, the trail should meander from one side to the other to add variety to the user experience and take advantage of potential scenic overlooks.

b. Layout of trail on ascending or descending grade:

• When locating sections of trail on a side slope, first define the percent of rise or fall, example 5%. 10% grades are used for short sections (20-50 linear feet) to avoid large trees or rock outcrops. As much as possible, locate the trail route on the uphill side of trees growing on slopes to prevent damage to the root systems. You must have a 2-person crew to perform this layout. First person (#1) is the instrument operator (using clinometer) and the second person (#2) is the range pole holder. Standing on level ground, the range pole is marked with flagging tape at the eye level of the instrument operator. Once at the trail location, #1 stands on the trail route and #2 moves forward along the trail route approximately 25-30 feet from #1. #2 moves up or down the slope in order to obtain the required grade incline and marks that spot. #1 moves forward to that location and the process is repeated. Grade reversals (water dips) should take place along the trail route every 100 linear feet to route water off the trail. Every 600-800 linear feet of ascent or descent, a level section of 100-200 linear feet is needed to provide a rest from the climb or descent.

• Side hill construction of trail tread is required if the slope of the hill the trail transverses is more than 5%. The way to measure the side slope of a hill or ridge is to lay a tool on the ground and then take the clinometer and place it on the handle of the tool. The percent slope will determine the depth of cut to construct the trail tread “all in cut”. All in cut refers to the process of not using any fill material for the width of the trail tread. See Figure 4 on page 26.

c. General guidelines for graded trail layout on side slopes.

• The optimum trail gradient on slopes is 5 – 10% (5 to 10 feet change in elevation per 100 feet in horizontal distance). Grades steeper than 10 % have much higher erosion potential, should only be used for short distances and may require special construction techniques such as steps made of stone.

• The length of space available to construct a trail section on grade is important. A gentler grade can be maintained on a broad mountainside compared to one in a narrow hollow.

• If the length of a graded section of trail is 1,000 feet or more, keep the slope gradient of the trail as low as possible and use reverse grade dips as a way to move water off the trail at regular intervals.

• All efforts should be made to avoid switchbacks. However, where space is limited or obstacles are present, construct switchbacks in areas of sufficient soil depth to maintain the trail to bypass boulders or rock outcrops.

• Ideally, switchbacks are located in dense brush or through other obstacles to prevent trail users from shortcutting the switchback. Avoid short switchback sections of less than 500 feet. Grades can be increased up 20% for short distances entering and exiting the switchback to increase the elevation change and broaden the distance between the upper and lower trails.

Once the preliminary route has been marked, 1 or 2 additional trips should be made to finalize the route. Only when the route has final approval from the managing agency should trail construction begin.

arrow Download the complete 40 page illustrated Pathways to Trail Building handbook (pdf 4.9 mb)

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