Presenter/s: Stewart Rood
Symposium Session: 2023 - 10 Charismatic Megaflora: Cottonwoods Restoration
Topics covered: canada, cottonwoods, flow augmentation, and riparian
The transboundary Columbia River system is one of North America’s most extensively dammed watersheds. The 1961 Columbia River Treaty between Canada and the United States was intended to further regulate the river system, through the construction of three large dams in British Columbia: Mica, Keenleyside, and Duncan (producing Kinbasket, Arrow and Duncan Reservoirs, respectively); and Libby Dam in Montana (Koocanusa Reservoir).
The original Treaty objectives were flood control and hydropower generation, and with the current Treaty modernization, a third objective is proposed, ecosystem function. For this objective, riparian woodlands provide the richest regional wildlife habitats, along with favored cultural, social, and economic resources. Cottonwoods, riparian poplar trees, provide the foundation for the floodplain forests, and this presentation will consider aspects of cottonwood adaptation and ecophysiology that provide a foundation for the prescription of dam operations for riparian enhancement. The presentation will then consider: (1) the implementation of functional flow regimes for ecosystem enhancement downstream from Libby Dam and Duncan Dam, and (2) prospects to manage reservoir regimes to promote riparian vegetation in the ecologically barren drawdown zones, thus ‘regreening the reservoirs’.
The reservoir vegetation enhancement strategy relies on understanding the inundation tolerances of the native and introduced riparian trees, shrubs, and herbaceous plants. Subsequent modeling to project outcomes from prospective operational scenarios also requires mapping of the topography and physical conditions for the upper drawdown zones, to assess influences including bank slopes, sediment types, stream inflows, and seed sources. Analyses of the feasibility for operational changes should then consider balancing relative to the three objectives of flood control, hydropower, and ecosystem function; as well as some contrasting influences on the reservoirs upstream and the rivers downstream from the Treaty dams.