Dam footprint impact summary BC Hydro dams in the Columbia Basin

Author: G. Utzig, D. Schmidt

The project is composed of five broad elements: 1) mapping of basic aquatic and terrestrial ecosystems within the dam footprints; 2) assessing changes in primary productivity; 3) assessing changes to aquatic and terrestrial habitats; 4) assessing impacts on individual fish and wildlife species; and 5) the identification of compensation options. This report is a summary of thirteen previous reports that document individual components of the five elements.

Pre-dam aquatic, wetland/floodplain and terrestrial ecosystems were mapped from pre-dam information sources, including aerial photographs, topographic maps and land class mapping. The ecosystem mapping demonstrated that each reservoir was unique with regard to the types, amounts and proportions of ecosystems impacted. The Arrow and Kinbasket Reservoirs occupy the largest footprints at 51,270 and 42,650 ha respectively. The Revelstoke (11,450 ha), Duncan (7,300 ha) and Koocanusa (6,685 ha) reservoirs are also fairly extensive. The Whatshan (1,770 ha) and Pend d’Oreille (430 ha) are somewhat smaller, and Kootenay Canal, Aberfeldie, Elko, Cranberry, and Spillimacheen reservoirs are less than 50 ha each (because of lack of data, footprint impacts of Aberfeldie, Elko and Cranberry are not discussed in the report). The pre-dam ecosystem composition of the Arrow and Whatshan Reservoirs were dominated by pre-existing lakes, while the Kinbasket, Revelstoke, Koocanusa, Pend d’Oreille, and Spillimacheen were dominated by forested ecosystems and large river systems, and the Kootenay Canal by forested ecosystems. The Duncan footprint included a complex mix of lakes, forests and wetlands. All footprints included varying lengths of river and/or stream ecosystems.

Overall pre-dam gross primary productivity within the dam footprints was estimated at approximately 870,000 tons of C/yr, with approximately 95% of that from forested ecosystems. Post-dam reservoirs have an estimated gross primary productivity of about 29,600 tons of C/yr, resulting in a net loss of over 840,000 tons of C/yr. Variation in primary productivity changes between reservoirs was principally dependent on footprint area and the proportion of forested ecosystems.

Lentic (lake/reservoir) habitat has been significantly increased in area, from 41,450 ha to 110,800 ha. However, the diversity and type of lentic habitats has been altered, with 12 lakes being replaced by 12 reservoirs. Changes in littoral habitats vary from reservoir to reservoir. Littoral habitats within storage reservoirs are subjected to larger variations in water levels than natural lakes, while most of the run of the river reservoirs and regulated Kootenay Lake, have water level stability similar to or more than that of comparable natural lakes in the region, including some lakes that were inundated. A risk assessment, based on losses as a proportion of similar terrestrial habitats available in the Columbia Basin, demonstrated that across the various dam units, lossinduced risks were: very high for very wet forests (4780 ha, 19%), wetlands (7700 ha, 26%) and gravel bars (3660 ha, 53%); high for wet forests (28,760 ha, 10%), black cottonwoods (5530 ha, 21%) and shallow water/ponds (1070 ha, 31%); and medium high for intermediate forests (15,660 ha, 2%). Losses of lake and river shoreline habitats were rated high for Kinbasket (980 km) and Arrow (680 km) reservoirs, while Revelstoke (350 km), Duncan (200 km) and Koocanusa (310 km) were rated medium high. Within the drawdown zones of some reservoirs there have been new ecosystems established, especially in the Revelstoke Reach of the Arrow Reservoir. Even though some of these simplified communities produce large quantities of vegetation, their value for higher trophic levels is limited.

Impacts were assessed in detail for 5 fish species, and to a lesser extent for 19 other species. The major impacts reported include loss of riverine habitat affecting some stage of the life history (e.g., kokanee, rainbow trout, bull trout, sculpins, dace, minnows, suckers), nutrient losses (e.g., kokanee, piscivorous rainbow trout, bull trout, sculpins, chubs), changes in flow regimes (e.g., white sturgeon), changes in water quality/turbidity (e.g., white sturgeon, rainbow trout, kokanee, mountain whitefish, sculpins), habitat/population fragmentation (e.g., white sturgeon, bull trout, rainbow trout), and entrainment (e.g., kokanee). In contrast, species that were able to take advantage of the extensive increases in lentic habitat, may have benefited from reservoir establishment in some situations (e.g., kokanee, burbot, lake chub, bull trout).

Wildlife impacts were evaluated for 289 vertebrate species using habitat loss information and species-habitat associations. Sixty-four Priority 1 species including: 3 amphibians, 1 reptile, 45 birds and 15 mammals had high habitat impacts, and agency emphasis for conservation and/or management. Forty-six Priority 2 species including 38 birds and 8 mammals had high habitat impacts, but were low agency conservation or management priority. Species with the highest habitat impacts were wetland and riparian specialists such as amphibians, waterbirds, waders, songbirds, bats and aerial insectivores. Overall species impacts mirrored substantial habitat losses, particularly in Kinbasket, Arrow and Duncan dam units.

The dams had significant impacts on ecological functions and processes. These include altered annual hydrologic regimes and floodplain processes, as well as disrupted biological processes such as natural disturbance regimes, trophic dynamics and nutrient cycling. The dams and reservoirs have impacted functions for individual species and populations, including seasonal migrations, genetic exchange, predator/prey relationships, reproduction and dispersal. These impacts can extend into non-impacted watershed units, especially those downstream of dams and reservoirs (e.g., Kootenay Lake, lower Columbia River).

Pre-dam aquatic, wetland/floodplain and terrestrial ecosystems were mapped from pre-dam information sources, including aerial photographs, topographic maps and land class mapping. The ecosystem mapping demonstrated that each reservoir was unique with regard to the types, amounts and proportions of ecosystems impacted. The Arrow and Kinbasket Reservoirs occupy the largest footprints at 51,270 and 42,650 ha respectively. The Revelstoke (11,450 ha), Duncan (7,300 ha) and Koocanusa (6,685 ha) reservoirs are also fairly extensive. The Whatshan (1,770 ha) and Pend d’Oreille (430 ha) are somewhat smaller, and Kootenay Canal, Aberfeldie, Elko, Cranberry, and Spillimacheen reservoirs are less than 50 ha each (because of lack of data, footprint impacts of Aberfeldie, Elko and Cranberry are not discussed in the report). The pre-dam ecosystem composition of the Arrow and Whatshan Reservoirs were dominated by pre-existing lakes, while the Kinbasket, Revelstoke, Koocanusa, Pend d’Oreille, and Spillimacheen were dominated by forested ecosystems and large river systems, and the Kootenay Canal by forested ecosystems. The Duncan footprint included a complex mix of lakes, forests and wetlands. All footprints included varying lengths of river and/or stream ecosystems.

Overall pre-dam gross primary productivity within the dam footprints was estimated at approximately 870,000 tons of C/yr, with approximately 95% of that from forested ecosystems. Post-dam reservoirs have an estimated gross primary productivity of about 29,600 tons of C/yr, resulting in a net loss of over 840,000 tons of C/yr. Variation in primary productivity changes between reservoirs was principally dependent on footprint area and the proportion of forested ecosystems.

Lentic (lake/reservoir) habitat has been significantly increased in area, from 41,450 ha to 110,800 ha. However, the diversity and type of lentic habitats has been altered, with 12 lakes being replaced by 12 reservoirs. Changes in littoral habitats vary from reservoir to reservoir. Littoral habitats within storage reservoirs are subjected to larger variations in water levels than natural lakes, while most of the run of the river reservoirs and regulated Kootenay Lake, have water level stability similar to or more than that of comparable natural lakes in the region, including some lakes that were inundated. A risk assessment, based on losses as a proportion of similar terrestrial habitats available in the Columbia Basin, demonstrated that across the various dam units, lossinduced risks were: very high for very wet forests (4780 ha, 19%), wetlands (7700 ha, 26%) and gravel bars (3660 ha, 53%); high for wet forests (28,760 ha, 10%), black cottonwoods (5530 ha, 21%) and shallow water/ponds (1070 ha, 31%); and medium high for intermediate forests (15,660 ha, 2%). Losses of lake and river shoreline habitats were rated high for Kinbasket (980 km) and Arrow (680 km) reservoirs, while Revelstoke (350 km), Duncan (200 km) and Koocanusa (310 km) were rated medium high. Within the drawdown zones of some reservoirs there have been new ecosystems established, especially in the Revelstoke Reach of the Arrow Reservoir. Even though some of these simplified communities produce large quantities of vegetation, their value for higher trophic levels is limited.

Impacts were assessed in detail for 5 fish species, and to a lesser extent for 19 other species. The major impacts reported include loss of riverine habitat affecting some stage of the life history (e.g., kokanee, rainbow trout, bull trout, sculpins, dace, minnows, suckers), nutrient losses (e.g., kokanee, piscivorous rainbow trout, bull trout, sculpins, chubs), changes in flow regimes (e.g., white sturgeon), changes in water quality/turbidity (e.g., white sturgeon, rainbow trout, kokanee, mountain whitefish, sculpins), habitat/population fragmentation (e.g., white sturgeon, bull trout, rainbow trout), and entrainment (e.g., kokanee). In contrast, species that were able to take advantage of the extensive increases in lentic habitat, may have benefited from reservoir establishment in some situations (e.g., kokanee, burbot, lake chub, bull trout).

Wildlife impacts were evaluated for 289 vertebrate species using habitat loss information and species-habitat associations. Sixty-four Priority 1 species including: 3 amphibians, 1 reptile, 45 birds and 15 mammals had high habitat impacts, and agency emphasis for conservation and/or management. Forty-six Priority 2 species including 38 birds and 8 mammals had high habitat impacts, but were low agency conservation or management priority. Species with the highest habitat impacts were wetland and riparian specialists such as amphibians, waterbirds, waders, songbirds, bats and aerial insectivores. Overall species impacts mirrored substantial habitat losses, particularly in Kinbasket, Arrow and Duncan dam units.

The dams had significant impacts on ecological functions and processes. These include altered annual hydrologic regimes and floodplain processes, as well as disrupted biological processes such as natural disturbance regimes, trophic dynamics and nutrient cycling. The dams and reservoirs have impacted functions for individual species and populations, including seasonal migrations, genetic exchange, predator/prey relationships, reproduction and dispersal. These impacts can extend into non-impacted watershed units, especially those downstream of dams and reservoirs (e.g., Kootenay Lake, lower Columbia River).