Teck Cominco Riverbank Restoration Project

Vegetated riprap installation riverbank,

spring 2006

Machine assisted brush layers installation riverbank, spring 2006

The soil bioengineering structures consist of brush layers planted using a mixture of Black Cottonwood and Willow species. Straw wattles were also installed across the slope between every second brush layer. These are designed to disperse surface water and act as sediment traps, reducing the risk of surface flow leading to rill erosion. The hillside units were also planted with native shrubs and conifer trees and hydro-seeded with native grasses. Due to the dry conditions on this site during the summer, an irrigation system was installed over all areas.

In 2007, trials using pulp-mill biosolids as a soil amendment were carried out in the more contaminated areas of Unit 3. Due to favourable results obtained here, this material was used extensively in Unit 1 (2008) during brush layer installation in areas where the soil had higher levels of contamination. A total of 300 cubic meters of this material was applied to this unit.

A total of approximately 148,000 live cuttings, 11,900 shrubs and tree seedlings were planted in Units 1 to 4 between 2006 and 2008 over an area of 3.29 ha.

Brush layer planting with Spyder Hoe in Unit 3, spring 2007

Brush layer planting in Unit 1, spring 2008

Straw wattles installed to control surface erosion

Repair and Maintenance:

Due to surface rill erosion in some areas, resulting mainly from irrigation water flowing over soil with poor grass cover (due to soil toxicity), repair / maintenance treatments were needed on the hillside units in the spring and fall of 2008. These consisted primarily of placing coir matting over critical areas and the installation of additional straw wattles, some of which included burlap splash aprons (these aprons improve the effectiveness of wattles in steep areas).

Monitoring Results:

Riverbank Sections:  As of August 2008, survival and growth of the soil bioengineering structures installed in the riverbank sections has been good to excellent overall. In some areas, however, survival was reduced due to prolonged river flooding. When the brush layers were submerged by water during flooding, survival was still good if the top of growing shoots remained above the water. Additional monitoring took place until the Fall of 2014. 

Riverbank Section 1A South, August 2008

Hillside Units 2 to 4:  Survival and growth of brush layers planted in Units 2, 3 and 4 was highly variable when assessed in August 2008 (these brush layers had two seasons of growth at this time). The average survival rate of planted cuttings, based on data collected in 11 permanent sampling plots, was 42 %. This value is considered only a rough estimate, as the S. D. (24 %) and range (7 % to 86 %) were high. Some areas with very good survival and growth were present, along with areas with very poor survival and growth. High mortality in some areas is thought due to one or more of the following: high soil metal concentrations, very hot and dry conditions during the summer of 2007 combined with poor irrigation coverage, heavy grass competition, and high soil salinity levels.

Hillside Unit 4, August 2008

Hillside Unit 1 North, August 2008

Compost Tea Application:

The importance of a healthy soil (and foliar) microbial community to proper ecosystem functioning is well recognized. Compost tea is a technology developed to help replenish and restore this community on lands where it is degraded – plant growth is typically improved with tea applications containing the correct mix of beneficial organisms for the vegetation being grown (Ingham, 2005). Compost Tea production is a “cold brewing” process, allowing growth of organisms extracted from the compost. Various organic foods / organic fertilizers are added during the brewing process to provide food & nutrient substrates for the microbial organisms to grow. The degree to which fungal growth, versus bacterial growth, is sustained during the brewing process will depend on the quality of the initial compost used and the type of food / nutrients added. It is important that the process remain aerobic during the brewing process and up until the tea is applied – if the tea becomes anaerobic, beneficial organisms (aerobic fungi, protozoa and nematodes) may be lost, replaced by anaerobic bacteria and yeasts (Ingham, 2005).

Given the contaminated nature of the soil and lack of vegetation in the Riverbank Restoration Project area prior to the present reclamation treatments, restoration of the microbial community here is considered a vital component of the project. To help achieve this, three compost tea applications are scheduled for each year until 2011. As of fall 2008, five compost tea applications have been done (two in 2007 and three in 2008). The compost tea is applied through injection into the irrigation system.