Arrow Lakes Reservoir Mid-Elevation Scenarios: Scoping Evaluation

Author: A. Thomson, G. Utzig, B. Green, N. Kapell

This report expands on previous stabilized Arrow reservoir studies, particularly the BC Hydro study, and discusses the main issues associated with two distinct constant elevation scenarios in more detail while making recommendations as to further study. This report only examines potential effects of stabilized, mid-elevation Arrow reservoir with the Arrow reservoir area between the Revelstoke and Hugh L. Keenleyside Dams. Significant potential upstream (Kinbasket reservoir) and downstream (transboundary reach) effects of these scenarios were determined to be out of scope for this project.

In order to reach overall conclusions about both Scenarios when compared to the current ALR operational regime, the values impacted by the Scenarios are summarized in Table 8 below as having a Positive or Beneficial Impact, Neutral Impact, Mixed or Uncertain Impact , or Negative Impact. The values were assessed using similar directional methodology in the BC Hydro’s Technical Studies reports (BC Hydro 2013b).
Most of the assessed value results are either positive or mixed/uncertain when compared to the current ALR operational regime. There are also some neutral and negative aspects of the Scenarios. In both scenarios, the successful establishment of riparian vegetation is seen to heavily influence several values in a positive direction, such as erosion, wildlife (ungulates and birds), dust generation, archaeological sites, and fish access into tributaries. Scenario 2 encourages a more robust and permanent mature riparian vegetation community when compared to Scenario 1. Vegetated reservoir banks and shorelines are less prone to wind and wave erosion, and dust generation above the constant elevation would be reduced, more so with Scenario 2. Terrestrial wildlife habitats would increase, notably ungulate winter range because of improved riparian vegetation. Archaeological sites above the base elevation would be better protected from wind and wave erosion and conceal artifacts from pothunters due to establishment of riparian vegetation, more so for Scenario 2. However, since vegetation would not establish within a few feet of the constant elevation, archaeological sites within this zone would be severely degraded or completely lost absent mitigation measures. Tributary stream banks are expected to stabilize with mature vegetation establishment under Scenario 2, which would aid fish access to spawning sites.
Some other values not directly associated with riparian vegetation establishment also move in a positive direction. Commercial navigation is improved equally under both Scenarios, and annual power generation at Arrow Lakes Generating Station is expected to be slightly higher under Scenario 2 than annual power generated under the current operational regime. Agricultural opportunities are expected to increase under both Scenarios, more so for Scenario 2. Bird nest flooding, a concern in the Revelstoke Reach, will decrease for nests above the base constant elevation in non-flood years in both Scenarios. Scenario 2 offers better nest flooding protection over Scenario 1. Herptiles, shorebirds and waterbirds should have better access to wetlands and ponds above the base constant elevation for both Scenarios in non-flood years.
Although there are positive attributes to the scenarios, and in particular Scenario 2, analysis of some values found mixed or uncertain outcomes when compared to the existing ALR operational regime. For both scenarios, most fish related values are uncertain (could be either positive or negative) or mixed, in particular pelagic primary and secondary productivity, kokanee biomass, aquatic productivity values in the Revelstoke Reach, and fish spawning and migration habitat conditions in the lower reaches of tributaries for Scenario 1. At the scoping level it is very difficult to evaluate the combined effects of multiple potential changes. Additional research that includes ALR ecosystem modelling, seasonal analysis of fish population life history requirements in the Revelstoke Reach for current operations and two Scenarios, and a comprehensive assessment of risks to current fish stocks and aquatic ecosystems associated with the two Scenarios is required.
Other values that are mixed include shoreline owners’ use of waterfront properties. Both Scenarios offer more certainty and consistency over access to the water since it is not fluctuating as under current conditions. However the water’s edge would be farther during summer months and closer during winter months than under current conditions. Under both Scenarios, the frequency and magnitude of mass wasting events are also mixed.
Burbot spawning and incubation success will unlikely to be affected by the both Scenarios, and ALGS annual power generation is roughly equal to current annual generation under Scenario 2.
The Scenarios also pose challenges to some values. Flood storage capacity would be reduced almost equally in both Scenarios when compared to current operations, and invasive vegetation species may become established without aggressive revegetation. Shoreline property owners and marina operators would prefer a higher constant elevation than evaluated in this report.
Although this report examines two constant elevation Scenarios that are similar in elevation, it is possible that additional incremental benefits and value tradeoffs may occur from an alternative constant elevations. In general, increasing the constant water elevation level above 1,425 ft. (434.3 m.) would benefit power production, marina operations, and shoreline property owners, but at the expense of less permanent large riverine and wetland habitat in the Revelstoke Reach, flood storage capacity, potential agricultural development, and low gradient stream fish habitat. If the constant elevation were lower than 1,420 ft. (432.8 m.), benefits would increase for wetlands, agricultural development potential, flood storage capacity and low gradient stream fish habitat. However these increases would be at the expense of commercial log transport through the Narrows, power production and waterfront land owners’ access to the water. It remains unclear the implications of alternate constant water elevations on pelagic fish resources.
In addition to assessing alternative constant elevation Scenarios, other alternatives could also be considered. For example to increase flood storage in the key flood years (1 in 5 years or 1 in 7 years in these Scenarios), there could be an option to drawdown the reservoir 5 or 10 ft. (1.5 – 3 m.) in March or April to increase storage. Alternatively, or in addition, there could be more variation in the “constant” elevation on an annual basis, with a drawdown of 5-10 ft. (1.5 – 3 m.) every year in March or April and/or short-term flooding of 5-10 ft. (1.5 – 3 m.) at freshet to provide for a more natural hydrograph and an increase in annual storage and power production. In Scenario 2 this would still allow for all the vegetation, wildlife and agricultural benefits above 1,430 ft. (435.9m.) The consideration of these types of scenario modifications will require further in-depth analysis; for example, a March -April drawdown operation could be harmful for kokanee whereas a short-term storage operation could be beneficial.

In order to reach overall conclusions about both Scenarios when compared to the current ALR operational regime, the values impacted by the Scenarios are summarized in Table 8 below as having a Positive or Beneficial Impact, Neutral Impact, Mixed or Uncertain Impact , or Negative Impact. The values were assessed using similar directional methodology in the BC Hydro’s Technical Studies reports (BC Hydro 2013b).
Most of the assessed value results are either positive or mixed/uncertain when compared to the current ALR operational regime. There are also some neutral and negative aspects of the Scenarios. In both scenarios, the successful establishment of riparian vegetation is seen to heavily influence several values in a positive direction, such as erosion, wildlife (ungulates and birds), dust generation, archaeological sites, and fish access into tributaries. Scenario 2 encourages a more robust and permanent mature riparian vegetation community when compared to Scenario 1. Vegetated reservoir banks and shorelines are less prone to wind and wave erosion, and dust generation above the constant elevation would be reduced, more so with Scenario 2. Terrestrial wildlife habitats would increase, notably ungulate winter range because of improved riparian vegetation. Archaeological sites above the base elevation would be better protected from wind and wave erosion and conceal artifacts from pothunters due to establishment of riparian vegetation, more so for Scenario 2. However, since vegetation would not establish within a few feet of the constant elevation, archaeological sites within this zone would be severely degraded or completely lost absent mitigation measures. Tributary stream banks are expected to stabilize with mature vegetation establishment under Scenario 2, which would aid fish access to spawning sites.
Some other values not directly associated with riparian vegetation establishment also move in a positive direction. Commercial navigation is improved equally under both Scenarios, and annual power generation at Arrow Lakes Generating Station is expected to be slightly higher under Scenario 2 than annual power generated under the current operational regime. Agricultural opportunities are expected to increase under both Scenarios, more so for Scenario 2. Bird nest flooding, a concern in the Revelstoke Reach, will decrease for nests above the base constant elevation in non-flood years in both Scenarios. Scenario 2 offers better nest flooding protection over Scenario 1. Herptiles, shorebirds and waterbirds should have better access to wetlands and ponds above the base constant elevation for both Scenarios in non-flood years.
Although there are positive attributes to the scenarios, and in particular Scenario 2, analysis of some values found mixed or uncertain outcomes when compared to the existing ALR operational regime. For both scenarios, most fish related values are uncertain (could be either positive or negative) or mixed, in particular pelagic primary and secondary productivity, kokanee biomass, aquatic productivity values in the Revelstoke Reach, and fish spawning and migration habitat conditions in the lower reaches of tributaries for Scenario 1. At the scoping level it is very difficult to evaluate the combined effects of multiple potential changes. Additional research that includes ALR ecosystem modelling, seasonal analysis of fish population life history requirements in the Revelstoke Reach for current operations and two Scenarios, and a comprehensive assessment of risks to current fish stocks and aquatic ecosystems associated with the two Scenarios is required.
Other values that are mixed include shoreline owners’ use of waterfront properties. Both Scenarios offer more certainty and consistency over access to the water since it is not fluctuating as under current conditions. However the water’s edge would be farther during summer months and closer during winter months than under current conditions. Under both Scenarios, the frequency and magnitude of mass wasting events are also mixed.
Burbot spawning and incubation success will unlikely to be affected by the both Scenarios, and ALGS annual power generation is roughly equal to current annual generation under Scenario 2.
The Scenarios also pose challenges to some values. Flood storage capacity would be reduced almost equally in both Scenarios when compared to current operations, and invasive vegetation species may become established without aggressive revegetation. Shoreline property owners and marina operators would prefer a higher constant elevation than evaluated in this report.
Although this report examines two constant elevation Scenarios that are similar in elevation, it is possible that additional incremental benefits and value tradeoffs may occur from an alternative constant elevations. In general, increasing the constant water elevation level above 1,425 ft. (434.3 m.) would benefit power production, marina operations, and shoreline property owners, but at the expense of less permanent large riverine and wetland habitat in the Revelstoke Reach, flood storage capacity, potential agricultural development, and low gradient stream fish habitat. If the constant elevation were lower than 1,420 ft. (432.8 m.), benefits would increase for wetlands, agricultural development potential, flood storage capacity and low gradient stream fish habitat. However these increases would be at the expense of commercial log transport through the Narrows, power production and waterfront land owners’ access to the water. It remains unclear the implications of alternate constant water elevations on pelagic fish resources.
In addition to assessing alternative constant elevation Scenarios, other alternatives could also be considered. For example to increase flood storage in the key flood years (1 in 5 years or 1 in 7 years in these Scenarios), there could be an option to drawdown the reservoir 5 or 10 ft. (1.5 – 3 m.) in March or April to increase storage. Alternatively, or in addition, there could be more variation in the “constant” elevation on an annual basis, with a drawdown of 5-10 ft. (1.5 – 3 m.) every year in March or April and/or short-term flooding of 5-10 ft. (1.5 – 3 m.) at freshet to provide for a more natural hydrograph and an increase in annual storage and power production. In Scenario 2 this would still allow for all the vegetation, wildlife and agricultural benefits above 1,430 ft. (435.9m.) The consideration of these types of scenario modifications will require further in-depth analysis; for example, a March -April drawdown operation could be harmful for kokanee whereas a short-term storage operation could be beneficial.