7.9 Select and Build Trail Structures 

7.9.1 Drainage 

Surface and subsurface water along the trail poses problems for construction and maintenance. Assess the nature and severity of potential drainage problems prior to finalizing the trail alignment and construction method. Use several proven techniques to control surface water drainage. Consider alternative design solutions for drainage structures. For example, reduce maintenance by using drainage dips instead of culverts. 

Crowns and Cross-slopes 

  • Trail surface crowns shed water in two directions. Crowns are suitable over level ground or where trail ditching is constructed on both sides of the trail.
  • Cross-slopes shed water to the outside of a slope. Prevent the formation of rutting on the trail by using crowns or cross-slopes.
Drainage Dips 

Drainage dips are incorporated into the trail tread during initial stages of construction by reversing the prevailing grade for a distance of 4-5 m or more. Drainage dips divert run-off from the trail tread. Drainage dips are effective, inexpensive, and do not detract from the natural setting. (See Detail #8

  • intercept water on slopes and shed it to the outside of the trail. Construct cross-drains with log rounds, squared rough-cut timbers, or local rocks. (See Detail #14)
  • Excavate a trench at an angle across the trail tread to place logs or rocks. Crossdrains should reinforce the correct angle and slope to allow the self-flushing of fine sediments. Place coarse granular fill or cobble rocks on the uphill side of the drain. Extend the porous material beyond the edge of the trail tread. Backfill around the drain structure as required. Ensure the drain structure is flush with the trail surface. Compact the backfill.
  • Avoid the use of log cross-drains on bicycle trails, since they may have a slick surface and cause cyclists to slip.
Table 8: Frequency of Cross Drains in Metres
Material Type Grade in %
2 4 6 8 10 12 15
loam 100m 50m 30m 25m 15m - -
sandy clay 150m 100m 75m 50m 30m 15m -
clay - 150m 100m 75m 50m 30m 25m
gravel or round rock - - 250m 150m 100m 75m 50m
shale or angular rock - - 275m 200m 125m 100m 75m
Figure 7: Typical Drainage Depression

7.9.2 Bridges, Culverts and Boardwalks 

  • Use bridges to cross rivers, streams, wetlands or areas of shallow water that are unsafe to cross, or where uncontrolled crossing would result in unacceptable environmental impacts. Consider stream flow characteristics, bank and stream bed erosion potential, fish habitat, peak run-off periods, snow loads and ice conditions. Provide adequate boat clearance on navigable watercourses. Select a suitable bridge design based on the expected type of use, span, available local materials and location.
  • Use plastic or metal culverts on small drainage ways, where drainage dips or other structures will not be adequate. Select a suitable size to accommodate seasonal high water levels, and set at a level that will not interfere with drainage. Place rocks around the ends of the culvert to stabilize the fill material and hide the ends of the pipes. Alternatively, cut the pipe ends back at a 45 degree angle to reduce the visual impact of the culvert. Place 10 cm of granular surfacing over the pipes.
  • Consider rock culverts constructed with local materials. Hand place rocks in an excavated trench to form a rock-bordered channel.
Simple Bridges 
  • Place stepping stones across minor drainage swales and streams. Avoid stepping stones if flood conditions would make the crossings impassable.
  • Construct bridges during the late summer or fall when the stream banks are dry and -stable. Record the spring high water mark and build the bridge at least .5 in above that mark where feasible.
  • Use one or two-log bridges where the crossing is relatively free of hazards, and the amount of use is low. On two-log bridges place the trunk stems in opposite directions for maximum strength.
  • Select trees that are straight and most uniform in diameter and with the least amount of branches. Peel the logs.
  • If the log is more than 12" in diameter at its thinner end, use one stringer. Otherwise, use two stringers side by side. Cut the corresponding notches in such a way that their sides, rather than the bottoms are touching. This will ensure a snug fit and will prevent rocking of the stringers sideways.
  • Top the logs by making cross-cuts with the chain saw, two inches apart, then cutting off the sections with an axe or a mattock. Use diagonal cross-cuts 1/4" deep over the flat surface of the topped log to prevent slipping.
  • Use rocks or soil fill to stabilize bridge ends.
  • Limit the bridge span according to the size of the log. Ensure the log spans over the water course and extends at least I metre over each bank. Secure the log ends with rock rip-rap or timber cribbing. Flatten the top surface of the logs for easier and safer walking. Construct a hand-rail on bridges over hazardous crossings.
  • Try to install the bridge abutments at the same level to prevent a slop across the bridge. Log bridges are slippery when wet.
Timber Bridges with Decking 
  • Construct log or timber bridges with decking for Type I foot trails, horse and bicycle trails. Place plank decking with 10-20 mm spacing for drainage and air circulation. Use timber wheel stops on low level crossings and hand-rails where the bridge is more than 1.2 m above the water.
  • Consider using raised galvanized metal brackets to hold stringers in place and help prevent wood rot.
  • Try to use one stringer span to cross creeks. Centre piers may cause debris to get caught in mid-stream, and the bridge may be swept away. If long enough stringers are not available locally, consider using a cable suspension bridge or other method. If flooding and debris are not a problem, support every bridge section longer than 4 m by a crib or gabion. Design bridges to support large mammals such as moose.
Figure 8: Single Log Bridge with Handrail
Table 9: Log Bridge Span Table
Span Minimum Log Diameter
2 - 6 m 250mm
6 - 8 m 325 min
 
  • Use custom designed bridges for spans over 5 in, or over hazardous waters. Consider suspension bridges for long spans to reduce construction and maintenance costs.
  • In wetland areas, allow for adequate drainage channels and variable water levels. Place the bridge above the maximum water level.
Cordwood Crossings 
  • Place peeled logs directly on the ground in approximately 2.5 to 3 in sections and secure with stakes at either end. Leave spaces of at least 35 cm between sections to allow for drainage channels.
  • Use log stringers or boulder edging with granular fill to contain trail treads in soft areas. This is called a turnpike: the parallel placement of peeled logs (min. of 20 cm) with a fifteen centimetre lift of rock placed in between for the tread surface. Depending on the type of trail use, place the logs either two or two and a half metres apart. Secure log stringers with wood stakes and set boulders well below the surface. Use this type of tread armor where ditches are required on both sides of the trail. Turnpike structures are less expensive than puncheons or corduroys.
Stringer and Decking Boardwalks 
  • Avoid open water bodies, except to provide interpretive or wildlife viewing opportunities.
  • In low use areas, or where soil conditions permit, place timber or log decking directly on sills. In higher use areas, or in wetter areas, construct a log or rock sill on the ground level. Secure stringers to the sill and fasten decking perpendicular to the stringers.
  • If log decking is used, split the logs and lay them down in an alternating fashion, first with the rounded side down, then up.
  • Use floatation devices in place of sills to cross areas of standing water. Consider airfilled drums or encased styrofoam blocks. Anchor floatation devices to the bottom of the water body.
  • Alternatively, drive posts into the bottom of the water body, and secure the bridge to posts with rings that allow the bridge to float up or down depending on water levels. If water levels do not fluctuate, fasten the bridge stringers to the posts.
  • Use flexible plank decking on walks over sand. This form of bridging helps to control erosion. Drill a lateral hole through each end of the planks and then string the planks together with twisted galvanized cable.
7.9.3. Steps, Ladders and Walls 
  • Construct steps on short, steep trail sections to ensure user safety and help prevent soil erosion.
  • Provide landings between short flights of 14 steps or less. Avoid long flights of stairs. Install handrails on at least one side of the steps where flights are steep or long.
  • Avoid stair flights with less than three steps since they may not be noticed by pedestrians.
  • Use acceptable riser height to tread depth proportions in step construction. Use a formula where the riser height times the tread depth equals 450 cm. For example, a rise of 10 cm requires a 45 cm tread depth, whereas a 15 cm rise requires a 30 cm tread depth. Ensure tread depths are at least 30 cm or more.
  • Design the steps to suit the terrain conditions, slope and intended type of trail use.
Log or Timber Risers 
  • Select logs or rough sawn timbers to build risers placed at grade. Excavate the route for the risers. Fasten the risers to the ground with iron rebars or connect the risers with timber supports or metal brackets. Backfill and compact the tread surface.
  • To build curved steps on a slope, follow the contour of the land to minimize site disturbance. Draw a lime line to show the desired curve. Use railway ties (15 cm x 20 cm) or other rough sawn timbers for the steps. Vary the spacing according to the slope.
Figure 9 Rise to Run Ratio for Steps

Steps on Stringers 

  • Use steps on stringers in high use areas or where rock, sand or roots make it difficult to set steps into the ground.
  • Use rough sawn, timbers and galvanized nails and bolts for all step construction.
  • Consider boulder steps if local rock is available. Set boulders into the slope. Fill the tread area with smaller rocks and granular material.
Ladders 
  • Use ladders on trails designed for more agile hikers where grades exceed a 1: 1 slope. Construct the ladder from on-site materials or build a timber slat and cable ladder.
  • Use a flexible cable and wood slat ladder on sand. This form of step helps to control erosion. Drill a lateral hole through each end of the wood slats or planks and then string the planks together with twisted galvanized cable.
Barriers 
  • Use trail edge barriers at hazardous sites such as cliffs. Consider barriers to protect ecologically sensitive areas from user traffic or to prevent vehicle access to nonmotorized trails. Construct barriers with logs, timbers, stones or boulders, depending on the availability of materials.
  • Use stiles and dodgeways to form barriers that block motorcycle access to foot trails.
Retaining Walls 
  • Use log or dry wall rock retaining walls where the leveling of necessary tread width will excessively steepen the downhill slope of the trail. Timber structures vary in complexity from a local single height log anchored with local stakes to walls composed of pressure treated logs and stakes, anchored with deadmen, up to four logs high. (See Details #26).