Karst management and road building (lesson 6)

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Learning objectives

This lesson discusses how the karst management principles you have been exploring can be integrated with road building. By working through this lesson you will be able to:

  • Recognize the major challenges and issues involved in building roads on karst terrain
  • Identify best management practices for locating roads, landings and quarries, based on the vulnerability of the karst
  • Identify best management practices for constructing roads, landings and quarries based on the vulnerability of the karst
  • Identify best management practices related to maintaining, deactivating and rehabilitating roads on karst terrain.

Introduction

There are four major sections to Lesson 6:

  1. Locating roads, landings and quarries
  2. Constructing roads, landings and quarries
  3. Maintaining roads
  4. Deactivating and rehabilitating roads

The recommended best management practices for each section are presented as brief summaries. You are encouraged to check the fuller descriptions in the Karst Management Handbook for British Columbia for more complete information.

Issues and challenges

What are some of the management issues associated with road building?

  • Preventing damage to surface and subsurface karst features
  • Minimizing soil erosion and sediment/debris transfer into underground drainage systems and subterranean karst habitats
  • Maintaining natural surface and subsurface drainage patterns
  • Maintaining surface and subsurface water quality and quantity
  • Avoiding caves with thin ceilings 
  • Inadvertently intercepting subsurface conduits or caves through road and quarry development
  • Preventing damage to surface karst features and cave decorations through blasting and/or vibrations from falling timber and hauling heavy loads
  • Disturbing cave-dwelling fauna (for example, bats) through blasting, construction, or hauling
  • Controlling public access to surface karst features and caves

What are some of the engineering challenges associated with road building?

  • Ground surface instability
  • Highly irregular bedrock topography beneath the overburden which can lead to unpredictable foundation depths
  • Road subsidence, collapse, or washout due to sinkhole development
  • Deep openings or shafts in the bedrock
  • Near-surface cavities and caves with thin ceilings 

Caves with thin ceilings are caves where the depth of the overlying bedrock is less than three times the width of the cave passage.

caves with thin ceilings (GIF, 19KB)

Locating roads, landings and quarries

What is the major challenge when planning the location of roads on karst terrain?

A major area of potential conflict with road locations is the fact that logging roads are often located along ridges and areas of higher elevation to achieve easier access to timber and maximum deflection for harvesting. These same locations are also where the greatest density of exposed epikarst is typically found. Ideally, roads should not be located on exposed, well-developed epikarst. However, in many cases, there may not be a viable alternative for locating the road. These two issues – the need to protect exposed epikarst and the need for efficient access to timber – require innovative management approaches. These are discussed in detail in the lesson on Constructing Roads, Landings and Quarries.

The following section summarizes the recommended best management practices for locating roads, landings and quarries. As these are only brief summaries, you should also check out more detailed information in the Karst Management Handbook for British Columbia.

Low and moderate vulnerability areas

The following best management practices are recommended:

  • Use existing roads, landings and quarries wherever possible.
  • Locate quarries on a site-specific basis while accounting for the nature of karst resources in the area.
  • Locate roads and landings to minimize deep cuts and fills.
  • Locate roads, landings and quarries to maintain natural surface drainage patterns as much as possible.
  • Avoid locating roads, landings, spoil sites and/or equipment turnaround/turnout sites near surface karst features, cave entrances, or exposed epikarst.
  • Avoid locating roads, landings and quarries within 100 metres of caves known to have fragile formations or known/suspected habitats of bats or other wildlife sensitive to disturbances.
  • Avoid facilitating public access to sensitive or hazardous karst areas.
  • Locate storage areas for fuel and other hazardous materials off karst terrain or at least on low vulnerability karst areas (except for daily fuel requirements).

High vulnerability areas

In addition to the recommendations for low and moderate vulnerability areas, the following best management practices are recommended on high vulnerability areas:

  • Limit the planning of new roads and landings to only those required for local timber access or for crossing short sections of high vulnerability karst.
  • Plan to use overlanding road construction techniques as much as possible on exposed epikarst.
  • Avoid locating mainline or long-term roads and landings on well-developed epikarst. Limit roads on these areas to temporary roads that can be readily rehabilitated
  • Avoid locating roads over caves known to have thin ceilings (see Figure 6-1)
  • Avoid locating roads over sinking streams, intermittent or ephemeral channels and dry valleys
  • Avoid locating bridge crossings at topographical low points
  • Avoid quarrying on high vulnerability karst if possible. (Use adjacent lower vulnerability karst areas or seek the advice of a qualified professional for appropriate site selection)

Constructing roads, landings and quarries

The following section summarizes the recommended best management practices for constructing roads, landings and quarries. As these are only brief summaries, you should also check out more detailed information in the Karst Management Handbook for British Columbia.

Low vulnerability areas

The following best management practices are recommended:

  • Conduct safety briefings for appropriate personnel
  • Flag karst features and/or values within the operating area
  • Notify the Forest Service district office if landslides or other disturbances occur which could affect karst features
  • Modify or cease operations if previously unidentified karst features or values are encountered during road, landing or quarry construction, and notify the Forest Service district office
  • Avoid construction activities during periods of heavy rainfall
  • Avoid importing ballast from non-karst terrain
  • Stabilize disturbed areas, such as quarries, to reduce erosion potential
  • When constructing temporary access structures, avoid karst features, maintain surface drainage patterns, and minimize runoff and erosion

Moderate vulnerability areas

In addition to the recommendations for low vulnerability areas, the following best management practices are recommended on moderate vulnerability areas:

  • Directionally fall and yard right-of-way trees away from roadside karst features
  • Pile surplus construction material away from surface karst features, exposed epikarst, and streams leading into features
  • Avoid drilling or blasting near karst features, or if this is not possible, use mitigative strategies such as delayed charges, blasting mats, etc
  • Use overlanding road construction methods near roadside karst features
  • Avoid fueling or servicing machinery near surface karst features and cave entrances
  • Keep the wheels or tracks of equipment at least 5 metres from the edge of roadside karst features. If not possible, keep wheels or tracks parallel to the edge of features.
  • Avoid removing gravel or fill from roadside depression features
  • Minimize clearing of roadside vegetation
  • Use sediment traps and vegetated infiltration areas to prevent road runoff entering exposed epikarst, surface karst features, cave entrances or sinking streams
  • Complete construction activities so that cut and fill slopes have time to revegetate before the wetter months of the year
  • Reduce road runoff by leaving roads on exposed carbonate bedrock unsealed. Use geotextile materials if sedimentation of groundwater is a potential hazard
  • Crown the surface of sealed roads to facilitate lateral diffuse drainage
  • Direct runoff from bridge decks away from stream channels and into vegetated cover along stream banks
  • Minimize potential sedimentation problems by using geotextile materials on bridge decks and around bridge ends
  • Avoid the use of chemically treated wood for bridges

High vulnerability areas

In addition to the recommendations for low and moderate vulnerability areas, the following best management practices are recommended on high vulnerability areas:

  • Exposed, well-developed epikarst should only be crossed by relatively short segments of temporary road that can be readily rehabilitated. Consider the following specialized road construction techniques:
  • Use overlanding road construction methods as much as possible
  • Avoid or minimize grubbing; flush cut stumps, and avoid pulling stumps
  • Minimize clearing widths, road widths and landing surface areas
  • Use the largest possible ballast material to build up roads, to span or infill epikarst cavities, and to minimize runoff from the road surface
  • Avoid using fine materials for road building
  • Roadside ditches are generally not necessary since runoff percolates directly into the bedrock
  • Obtain ballast material from nearby low or moderate vulnerability areas
  • Use geotextile materials to minimize sediment transfer into subsurface drainage systems
  • Consider the use of geogrids for spanning epikarst cavities
  • Consider using bridging mechanisms to raise or span roads over short sections of significant epikarst features
  • Where practical, use rock drilling/hammering instead of blasting on well-developed epikarst. Where blasting is used, seek the advice of a qualified professional
  • Post public warning signs and close areas while blasting near surface karst features or caves that may be used for recreation

Maintaining roads

The following section summarizes the recommended best management practices for maintaining roads. As these are only brief summaries, you should also check out more detailed information in the Karst Management Handbook for British Columbia.

Best management practices for all vulnerability categories

The following best management practices are recommended:

  • Maintain silt/sediment traps and drains to function properly, and dispose of accumulated debris away from karst features and watercourses leading to features
  • Minimize accumulations of graded materials along roadsides where sediment could enter features or watercourses leading to features
  • Avoid the use of chemical dust suppressants, de-icing agents and salt
  • Locate storage areas for fuel and other hazardous materials off karst terrain or at least on low vulnerability karst areas (except for daily fuel requirements)
  • Avoid fueling or servicing machinery near surface karst features and cave entrances

Deactivating and rehabilitating road

The following section summarizes the recommended best management practices for deactivating and rehabilitating roads. As these are only brief summaries, you should also check out more detailed information in the Karst Management Handbook for British Columbia.

Best management practices for all vulnerability categories

The following best management practices are recommended:

  • Consult the local Forest Service district office to discuss access management with regard to deactivating roads
  • Remove or frequently breach windrows on the outer edge of temporarily deactivated roads
  • Use strategies to prevent impacting karst features during temporary deactivation (for example, water bars, cross-ditches, inslopes or outslopes)
  • Use strategies to prevent sedimentation when permanently deactivating roads (for example, armouring drainage ditches)
  • Do not use quarries as storage sites for logging debris/wood waste, refuse, petroleum products, etc
  • Deactivate quarries upon completion of operations
  • Take measures to make deactivated quarries inaccessible to the public (for example, berms, waterbars)
  • Restore natural surface drainage patterns as much as possible to maintain the quantity and quality of subsurface flows
  • Avoid road rehabilitation during sustained or heavy rainfall
  • Avoid road deactivation or rehabilitation when disturbances to roadbeds may be detrimental to karst values in the area
  • Keep the wheels or tracks of equipment at least 5 metres from the edge of roadside karst features. If not possible, keep wheels or tracks parallel to the edge of features
  • Avoid introducing soil or bedding materials into karst features
  • Complete rehabilitation operations with sufficient time to allow for adequate revegetation before the wetter months of the year

Answer either True or False to check your understanding.

  1. The major area of potential conflict with building roads on karst is the lack of ballast material
  2. When locating quarries on high vulnerability karst, seek the advice of a qualified professional
  3. Removing gravel from roadside depression features is an acceptable practice
  4. The use of chemical dust suppressants, de-icing agents and salt is not recommended for roads on karst terrain
  5. Deactivated quarries can make good storage sites for logging debris, petroleum drums, etc
  1. False
  2. True
  3. False
  4. True
  5. False