| Abstract/Description or Keywords |
The Arrow Lakes Reservoir (ALR) is a vital part of the hydroelectricity generation and flood control dam complex on the Columbia River. The reservoir was created when the Hugh L. Keenleyside Dam was commissioned in 1968 as part of the Columbia River Treaty that was ratified and came into effect in 1964. Fifty years later, both Canada and the United States are assessing the Treaty, Treaty dams and examining alternatives to adjust facility operations to reflect current and projected economic, social and environmental values. This report examines one possible operational alternative for the ALR. The concept in its base form involves changing the ALR from a storage reservoir - where spring runoff is stored and released slowly over the fall and winter months - into a run-of-river operation where flows are passed through the reservoir largely unimpeded during years where the forecasted risk of flood damage is low. The reservoir water elevation would remain at a constant and stable elevation as opposed to the pre-dam hydrograph which fluctuated with the spring freshet. During forecasted high water years, the reservoir would be used to store excess water to reduce flood risk and the reservoir water elevation would rise and fall over a defined period. This report explores on a conceptual level how various key social, environmental and economic interests may be affected if this stable elevation concept were enacted. The report does not examine or analyse implications of a stable elevation concept on values or infrastructure above (i.e. Kinbasket reservoir) or below (i.e. lower Columbia R.) the ALR. The report scopes the implications of implementing an ALR constant elevation operational regime by analyzing existing data and reports, and interviewing stakeholders. Two similar Scenarios were examined: Scenario 1 holds the ALR water elevation at a constant 1,425 ft. (434.3 m.) year round with a small drawdown in the spring and fall periods, and a flood event to full pool once in five years; Scenario 2 holds the ALR water elevation slightly lower at 1,420 ft. (432.8 m.) year round with a flood event to full pool once in seven years. Main issues specific to the ALR – such as fisheries, power generation, archaeological resources, etc. – are assessed. In order to derive the greatest benefit for the most issues from a constant elevation concept, the report authors hypothesize that the constant elevation concept must allow the development and maintenance of a permanent, diverse and vigorous vegetated riparian zone (including trees and shrubs). It is further hypothesized that the frequency and duration of vegetation inundation determines vegetation species composition and diversity and survival probability. Based upon analysis of pre-regulation vegetation species spatial and elevation patterns along the Arrow Lakes along with water elevations and flood frequency, it is unlikely that Scenario 1 would allow mature forest vegetation to establish in the current drawdown zone. Scenario 2, which further limits the current drawdown zone inundation frequency and duration, will more likely encourage forested riparian vegetation establishment and permanence, although mature forest development will likely take a number of decades. Other ALR values, such as fish access into tributaries, wildlife, dust abatement and other values would then benefit as a result from riparian vegetation establishment. 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. 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 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 is the most comprehensive report to date on the ALR constant elevation concept, the report only scoped the issues using existing data collected and reports written for other purposes. As such, the report outcomes are directional only and not refined enough to determine magnitude of change and are certainly open for debate. More research and data analysis that is specific to understanding the outcomes of a constant elevation are required before uncertainties can be significantly reduced, starting with a more detailed analysis of historical vegetation patterns and flood events, and vegetation inundation and duration tolerance experiments to determine native riparian vegetation survival requirements and successional rates in the drawdown zone. Understanding mature vegetation tolerances and limitations would inform operational parameters of other values such as flood control. The report analysis is restricted to the ALR and does not analyse upstream or downstream values that would be clearly affected if a constant elevation concept were enacted in the ALR. Recommended future analysis of an ALR constant elevation concept should evaluate affected resources and values in all sections of the Columbia River upstream of the international border. |
