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7. SHORELINE STABILIZATION

CONTEXT

Shoreline stabilization refers to a variety of works designed to prevent or reduce erosion. These works include the preferred methods of bio-engineering or rip-rap, or a variety of vertical shore walls which are usually composed of armour stone, masonry rock, concrete, steel, wood, plastic, or gabion baskets.

While vertical shore walls have short-term benefits, the retention of existing emergent aquatic vegetation and planting of additional trees and shrubs on the shoreline bank (bio-engineering) is the preferred and most effective method of arresting and preventing further erosion in an environmentally responsible manner. Rip-rap, which is the placement of clean angular stone or rock rubble on a slope, may be used in combination with, or where bio-engineering methods alone would not be effective. Properly sized rip-rap placed along a waterfront over a geo-textile filter fabric is quite effective in dissipating wave action, and preventing soil particles from washing out while allowing land-based moisture to naturally percolate back into the water body.

The most damaging impacts of vertical shore walls as opposed to other methods of shoreline stabilization are:

  • Transformation and hardening of the shore;

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  • Encroachment onto the bed of the Canal or Waterway;
  • Alteration of the overall heritage character of the Canal or Waterway;
  • Disturbance/destruction of cultural resources;
  • Alteration, disruption or destruction (loss) of fish habitat;
  • Altered wave energy and current patterns;
  • Sediment transport, turbulence and scouring of the bottom;
  • Disruption of the life cycle of aquatic organisms, such as blocking access by amphibians and reptiles back and forth between water and land;
  • Short or long-term loss of native waterfront vegetation that plays an important role in preventing erosion and sheet runoff into the waterbody;
  • Poorly constructed walls are far more prone to damage due to frost-heaving, erosion when inundated by water or pounded by waves, and destruction by ice movement.

Parks Canada routinely approves environmentally sensitive shoreline stabilization measures.

POLICIES

  1. The retention of native shoreline vegetation, bio-engineering and rip-rap are, in order, the preferred methods for shoreline stabilization.
  2. Rip-rap is normally approved for shoreline stabilization subject to the following:
    • The material used is clean imported angular stone or rock between 10 and 45 cm (4 - 18 in) in size;
    • A geotextile filter fabric is to be installed under and behind the rock;
    • A 3:1 (horizontal : vertical) slope ratio is recommended and may not be steeper than 2:1 unless justifiably proposed in an accredited geo-technical report;
    • Excavation to create the slope shall be upland; excavation or dredging of the bed is not normally permitted;
    • Natural stone must be imported and not removed from the lake or river bed for shoreline stabilization.
  3. Encroachment of rip-rap shoreline stabilization onto the lake or river bed of up to 1 m (3 ft.) for shrubs and 1.5 m (5 ft.) for trees may be permitted if it can be demonstrated that:
  4. The encroachment is required to protect significant trees, shrubs and other natural vegetation threatened by erosion;
  5. The encroachment onto the bed will not harmfully affect fish or fish spawning sites;
  6. The shore stabilization work would result in the removal of significant natural shoreline vegetation;
  7. In exceptional circumstances an encroachment beyond 1.5 m (5 ft.) may be allowed if is supported by a geotechnical study.
  8. Other methods of shore stabilization may be considered if:
    • Bio-engineering or rip-rap have been considered and found to be unacceptable due to site conditions;
    • The work will be constructed upland of the high water mark and no encroachment onto the bed of the waterbody will occur;
    • The work will not alter the existing shoreline contours;
    • The work will not result in the removal of natural shoreline vegetation;
    • The work will not have a significant impact on the heritage character of the national historic site;
    • The shore wall will not result in the harmful alteration, disruption or destruction of fish habitat or other wildlife habitat;
    • The backfill will be clean imported material;
    • Filter cloth will be installed behind the work to prevent the migration of fines into the water;
    • Clean imported rip-rap or rock rubble, of a size approved by the Canal or Waterway and free of silts and organic debris, will be placed along the toe of the work to prevent scour and create aquatic habitat;
    • The construction of these works has been approved by the appropriate agency with jurisdiction over waterfront development.

    To rectify unique or unusually unstable slope issues, a geotechnical report will be required which may supercede the above slope stabilization policies


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