Okanagan river flow and mainstem lake levels are regulated by dams and other structures known as the Okanagan Lake Regulation System (OLRS). Lake management is challenging due to natural variability between wet and dry seasons, balancing lake outflows with ecosystem health, and using inflow forecasts that have uncertainty and are vulnerable to extreme weather events. The impacts of climate change are also posing new challenges for lake management. The worst flood and highest lake levels were recorded in 2017 following an atypical freshet driven by late season snow accumulation, heavy rain, and rapid snow melt and the worst drought and lowest lake levels were recorded in 2021. The OLRS is near the end of its lifespan, and it is important an updated system reflects societal priorities, respects Indigenous rights and title, and considers future climate change scenarios. To determine how climate change will impact lake levels and the existing regulation system, information from the 2020 OBWB Floodplain Mapping Report conducted by Northwest Hydraulic Consultants Ltd. (NHC) was utilized. The Floodplain Mapping Report used ECCC’s CanLEADV1 50-climate ensemble dataset for RCP 8.5 to analyze future climatic changes in the Okanagan Basin. The ensemble dataset was downscaled and used to drive a hydrologic model of the Okanagan River Basin from 1950 to 2100. The hydrologic model was calibrated to either standard lake regulation for current operating rules or future regulation which accounted for how climate change would alter basin hydrology. Based on the model results, while historically the 2017 event seems rare and extreme it becomes more common in the future. Furthermore, when considering lake regulation, maintaining standard regulation in the future could result in more consistent and extremely high lake levels compared to a future regulation system which would keep the Okanagan Lake below 2017 levels most of the time.
In 2021, following extensive flooding in 2017 and 2018 and drought in 2021, the Okanagan Basin Water Board (OBWB) and Government of BC launched a review of the Okanagan Lake Regulation System (OLRS) to modernize lake level management and consider future climate change. In the Okanagan Valley, river flow and Okanagan Lake levels are controlled by the OLRS. The OLRS is reaching the end of its lifespan and is challenging to manage because of natural variability, balancing lake levels and flow with ecosystem health and societal needs, and climate change which is increasing the frequency of flood and drought events. The Plan of Study report aims to modernize the OLRS and lake level management to reflect and address the impacts of climate change in the Okanagan Basin as well as current societal values and knowledge. A prior OBWB floodplain mapping study examined future climate change in the Okanagan Basin and revealed that under current OLRS management plans, more frequent flood and high lake level events would occur compared to a future management regime that would consider climate change. Therefore, significant changes to the OLRS are needed to mitigate climate impacts. To understand the most effective way to modernize the OLRS and lake management, the Plan of Study proposes 18 scientific and engineering studies occurring over a 7-year span. As of May 2022, several studies have been completed with more being conducted as funding is secured. As the Plan of Study is executed, it will be necessary to monitor emerging gaps and new knowledge and re-evaluate completed studies. The 18th and final study will outline the plan for OLRS modernization which will then be implemented.