Lake Winnipeg Shoreline Restoration

Shoreline Restoration Using Bioengineered Storm Plain Reinforcement

Background:
Lake Winnipeg is part of the most undeveloped and pristine watersheds of southern Canada encompassing 24,400 km².  It is the sixth largest freshwater lake within the borders of southern Canada and the 12th largest on the Earth.

Even with it’s vast size it is relatively shallow with a mean depth of 12 m.  The east side of the lake has pristine boreal forests and rivers that are being promoted as a potential United Nations World Heritage Park. The lake is elongated in shape, and is 416 km from north to south, with remote sandy beaches, large limestone cliffs which provides a location for bat caves in some areas.

Manitoba Hydro uses the lake as one of the largest reservoirs in the world. This giant and remote lake has tremendous ecotourism potential, with nothing else quite like it in southern Canada and in Manitoba.

Lake Winnipeg is a unique geological and geographical area that is largely undeveloped, and quite a rare ecological gem in the world today.  Lake Winnipeg drains northward into the Nelson River at an average annual rate of 2066 m3/s, and forms part of the Hudson Bay watershed which is one of the largest in the world.  The lake's watershed measures about 984,200 km², and covers much of Alberta, Saskatchewan, Manitoba, northwestern Ontario Minnesota and North Dakota.

Problem:
Because Lake Winnipeg is extremely long (fetch) and the predominant north winds can result in extremely large waves along the southern shores - a phenomenon known as a setup or wind tide. Setups greater than 1 m above normal lake levels have been recorded along many of southern Lake Winnipeg's recreational beaches. The associated high waves with their up-rush effects have caused considerable storm damage and shoreline erosion. The highest setups occur in the fall, when the northerly winds are strongest. If the winds die down suddenly, the waters rush northward, then withdraw  back in a process called seiching. The extreme energy of  this wave action has resulted in tremendous damage to the shoreline including the removal of vegetation, extensive loss of soil, and even property damage.

Solution:
Two fundamental observations associated with shoreline erosion on Lake Winnipeg have been made.  First, erosion occurs mainly during storm events that raised the level of the lake and pushed the water towards the shore.  Second, areas left with natural vegetation and gentle slopes shows the best resistance to these erosive storms.  This led to the solution; design a bioengineered storm plain with a 3:1 or flatter slope and revegetate it with native plants and willows to mimic the natural areas on the lake that were least effected by erosion.  Additionally the vegetations erosion control performance would be improved  with man-made engineered products.
To accomplish this task, a bioengineered system incorporating a rock toe and soft armored techniques that included the EnvirolokTM System of specialized vegetated sandbags, and native plants which include grasses, sedges, willows and dogwoods.

Built on a rock foundation, the EnvirolokTM Systems sandbags are filled with a soil mixture that supports vegetation but has a soil particle size larger than the holes in the geotextile fabric. This allows the vegetation to grow through while retaining the soil from being removed. The bags are locked together using the EnvirolokTM System.

In the lower impact zone where there is extensive wave energy  (usually 717 feet to 719 feet elevation) a combination of man-made and natural materials were needed to protect the soil.

First, the shoreline is re-graded and filled to provide the contour for a storm plain.  This new grading is then protected with a non-woven permeable geotextile, which provides a secondary line of erosion defense for the system. The EnvirolokTM System sandbags are placed, and secured with the locking and tying components of the system.  The system is then covered with a thin venire of topsoil and seeded with native grasses and sedges, which is then covered with erosion control matting.

Willow and Dogwoods are then planted in between the sandbags and grow into the parent soil creating a natural re-bar effect for the system, with their deep rooting structures. When fully established, the plants will provide yet another layer of energy absorbing (waves absorbing) protection for the shoreline.

Once fully vegetated the man-made materials in the storm plain system will be invisible, thoroughly hidden by the vegetative cover.  As the system matures, the vegetations root depth deepens and the system becomes continually stronger. With the aesthetic end results being a natural looking shoreline.