Author(s): Jean Morin; Marianne Bachand
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Abstract: Rainy Lake and Namakan Reservoir are large water bodies, covering more than 1500 km2, on which water-levels have been managed since 1949. The present rule-curve (2000RC) is being reviewed in order to consider its effect on the environment. In collaboration with several partners, we have developed a quantitative tool that uses a combination of 1D and 2D habitat models for evaluating the effect of water level fluctuations on the biota. It is called IERM: Integrated Ecosystem Response Model. Within the IERM, habitat models are driven by long term water-levels series representing measured levels, simulated natural levels and levels based on two rule-curves (2000RC and 1970RC) for the 1950-2012 periods. The modelling is based on a regular grid (10 m) on which several key variables are defined: water-levels, topography, hydroperiods (different time-scale), bottom slope and wind wave simulations for all possible conditions at a quarter-monthly time-step. We produced several 1D models that evaluates the effect of waterlevel changes on wild rice, common loon and muskrat. Based on literature, we identified the most sensitive period of their life cycle and analyzed the effects of water-level changes during these periods. With several collaborators, we also developed spatially explicit (2D models) that quantifies suitable areas for some taxa: wild rice, cattails, marshes, submerged and emergent plants as well as northern pike and walleye reproduction grounds. For these models, we used a combination of logistic regressions and several time-related processes (drowning, drying, vegetation succession etc). Using all this information, we have identified some fundamental properties of the system natural fluctuations and also the best characteristics of a water-level management that allowed the design of a new rule curve that allows to maximize environmental benefits for a given year. Similarly, multiyear water levels have also to be addressed; some species like the invasive cattails are favored when water levels are stable from year to year. After several years they become dominant in protected shallow water bays where wild rice is found. Multiyear variations of the mean water levels are essential to reduce cattail abundance. All this knowledge have been analyzed and challenged by local communities that have concerns for boating, damages and flooding of properties and a large interest in local fisheries sustainability. Local population and stakeholders have selected and recommended an acceptable new set of rule-curves for water levels management from several proposals.
Year: 2018