Impact of BC Hydro Dams on Terrestrial and Wetland Habitat in the Canadian Portion of the Columbia Basin: Assessing the Significance of Ecosystem Change

Author: D. MacKillop, J. Krebs, I. Manley, A. Waterhouse

Summary of terrestrial and wetland ecosystem loss within and among reservoir units Ecosystem losses were compared to current ecosystem distribution, and evaluated to determine the overall significance of impacts to each ecosystem. Data were primarily based on ecosystem mapping projects. For the areas lost due to the dams and their associated reservoirs, ecosystem mapping used historic air photos and maps (Ketcheson et al. 2005). Predictive Ecosystem Mapping (PEM), supplemented with Terrestrial Ecosystem Mapping (TEM), Terrain Resource Inventory Mapping (TRIM), Baseline Thematic Mapping (BTM), and black cottonwood forest inventory data, was used to assess current ecosystem distributions.

Overall Ecosystem Losses

In total, more than 121,650 ha were flooded for the construction of BC Hydro’s dams in the Columbia Basin. Less than half of that area (44%) was comprised of pre-dam lakes, rivers, and streams (53,130 ha, described in Thorley 2008). The remaining ~68, 474, ha was comprised of forests (51,443 ha), including 4,780 ha of Forested Wetlands; Wetlands, Gravel Bars, and Shallow Water (12,435 ha); Agriculture and Urban (3,717 ha); and Rock/Talus, Avalanche Features, and Grasslands (879 ha).

The largest terrestrial and wetland areas affected were in the Kinbasket and Arrow Dam Units, followed by the Revelstoke, Koocanusa, and Duncan Dam Units (Table 11). The area of terrestrial and wetland losses was approximately 2.5 times higher in the Kinbasket than in the Arrow, the next largest reservoir. Considerably smaller areas were flooded for the Whatshan, Kootenay Canal, Seven Mile, Elko, Aberfeldie, Cranberry, and Spillimacheen Dam Units.

When analysed by BEC variant, the greatest number of hectares lost were in the ICHwk1, ICHmw1, ICHmw2, ICHmm, ICHmw3, and ICHvk1. All but the ICHmw2 are prominent in the Kinbasket Dam Unit, although the ICHmw2 formed a large portion of the Arrow and Duncan Dam Units. In the East Kootenay Trench, the PPdh2 and IDFdm2 were the most affected BEC variants where they comprised the majority of the area flooded for the Koocanusa Reservoir.

The highest Habitat Loss Risk Ratings were attributed to Gravel Bars, Wetlands (e.g., fens), Wet Forests (e.g., Cedar – Devil’s Club forests), black cottonwood Forests 7 , Shallow Open Waters, and Forested Wetlands (Cedar – skunk cabbage and/or Spruce – horsetail forests) (Figure 6 and 7). This pattern is consistent both basin-wide and across affected dam units, although higher impacts resulted when only the affected dam units were considered (Figure 7). In Basin wide analyses Shrub Steppe, Urban, Dry Forests, Rock/Talus, and Avalanche Features experienced very low to low Habitat Loss Risk Ratings while Wet Forests (dry climate) were rated moderate (Figure 6).

Across the entire basin, Wet Forests had the largest area flooded with almost 27,500 ha lost (Table 12). Most of this area, which includes many floodplains, black cottonwood stands, and cedar -spruce -devil’s club forests, were in the Kinbasket, Arrow, and Revelstoke Dam Units although losses were also large in the Duncan and Koocanusa Dam Units (Table 12). The next largest areas lost were Intermediate (mesic) Forests, and Wetlands. Wetlands and black cottonwood Forests are of particular concern since their current distribution across the Basin is considered to be relatively low and at risk (Jamieson et al. 2001). The area of Wetland losses was particularly high in the Kinbasket and Duncan Dam Units, while black cottonwood Forest losses were large in the Arrow (>1700 ha), Kinbasket (~1650 ha), and Duncan (>1400 ha) Dam Units. Flooding of Intermediate Forests was considerable in the Koocanusa, Arrow, and Revelstoke Dam Units. Other notable area losses include Gravel Bars, Agriculture, and Forested Wetlands in the Arrow Dam Unit (Table 12; Figure 6-7).

Overall Ecosystem Losses

In total, more than 121,650 ha were flooded for the construction of BC Hydro’s dams in the Columbia Basin. Less than half of that area (44%) was comprised of pre-dam lakes, rivers, and streams (53,130 ha, described in Thorley 2008). The remaining ~68, 474, ha was comprised of forests (51,443 ha), including 4,780 ha of Forested Wetlands; Wetlands, Gravel Bars, and Shallow Water (12,435 ha); Agriculture and Urban (3,717 ha); and Rock/Talus, Avalanche Features, and Grasslands (879 ha).

The largest terrestrial and wetland areas affected were in the Kinbasket and Arrow Dam Units, followed by the Revelstoke, Koocanusa, and Duncan Dam Units (Table 11). The area of terrestrial and wetland losses was approximately 2.5 times higher in the Kinbasket than in the Arrow, the next largest reservoir. Considerably smaller areas were flooded for the Whatshan, Kootenay Canal, Seven Mile, Elko, Aberfeldie, Cranberry, and Spillimacheen Dam Units.

When analysed by BEC variant, the greatest number of hectares lost were in the ICHwk1, ICHmw1, ICHmw2, ICHmm, ICHmw3, and ICHvk1. All but the ICHmw2 are prominent in the Kinbasket Dam Unit, although the ICHmw2 formed a large portion of the Arrow and Duncan Dam Units. In the East Kootenay Trench, the PPdh2 and IDFdm2 were the most affected BEC variants where they comprised the majority of the area flooded for the Koocanusa Reservoir.

The highest Habitat Loss Risk Ratings were attributed to Gravel Bars, Wetlands (e.g., fens), Wet Forests (e.g., Cedar – Devil’s Club forests), black cottonwood Forests 7 , Shallow Open Waters, and Forested Wetlands (Cedar – skunk cabbage and/or Spruce – horsetail forests) (Figure 6 and 7). This pattern is consistent both basin-wide and across affected dam units, although higher impacts resulted when only the affected dam units were considered (Figure 7). In Basin wide analyses Shrub Steppe, Urban, Dry Forests, Rock/Talus, and Avalanche Features experienced very low to low Habitat Loss Risk Ratings while Wet Forests (dry climate) were rated moderate (Figure 6).

Across the entire basin, Wet Forests had the largest area flooded with almost 27,500 ha lost (Table 12). Most of this area, which includes many floodplains, black cottonwood stands, and cedar -spruce -devil’s club forests, were in the Kinbasket, Arrow, and Revelstoke Dam Units although losses were also large in the Duncan and Koocanusa Dam Units (Table 12). The next largest areas lost were Intermediate (mesic) Forests, and Wetlands. Wetlands and black cottonwood Forests are of particular concern since their current distribution across the Basin is considered to be relatively low and at risk (Jamieson et al. 2001). The area of Wetland losses was particularly high in the Kinbasket and Duncan Dam Units, while black cottonwood Forest losses were large in the Arrow (>1700 ha), Kinbasket (~1650 ha), and Duncan (>1400 ha) Dam Units. Flooding of Intermediate Forests was considerable in the Koocanusa, Arrow, and Revelstoke Dam Units. Other notable area losses include Gravel Bars, Agriculture, and Forested Wetlands in the Arrow Dam Unit (Table 12; Figure 6-7).