Improving Lake Level Management in the Okanagan

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.

Understanding and Assessing Impacts

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.

Identifying Actions

The Floodplain Mapping Report made several initial operational recommendations for the OLRS system to manage future high flows. However, due to the complexity of the regulation system and how climate change is altering the Okanagan Basin hydrology, significant changes are needed. To understand the appropriate changes, the Plan of Study was compiled and reported in June 2021 by Associated Engineers Consultants Inc. The study was commissioned by the Okanagan Basin Water Board (OBWB) and Government of British Columbia and jointly funded by them. The Plan of Study proposes 18 scientific and engineering studies that will occur over a 7-year span to provide the required guidance to modernize the OLRS. The objective of the Plan of Study is to understand how to modernize lake management and the OLRS to reflect climate change and current societal values and knowledge, both scientific and Indigenous knowledge from the Syilx people. The Plan was developed after reviewing historical and current scientific and engineering studies about the Okanagan Basin and OLRS and discussing with an advisory group comprised of federal, provincial, Indigenous, and local governments. Many studies build on information from a previous study or previous work done in the Okanagan Basin, however the studies do not necessarily need to be completed in order. Additionally, the report does not include cost estimates and therefore a work plan, schedule, and budget will need to be developed for each study.

Implementation

As of May 2022, Study 7: refine mainstem lake bathymetry has been completed. Study 1: create linked Okanagan-Similkameen hydrologic model and Study 11: Okanagan mainstem flood risk assessment are in progress and almost completed. Study 2: Improve OLRS operating plan document will be underway in the summer of 2022. The OBWB is also applying for funding to continue progress on the Plan of Study.

Outcomes and Monitoring Progress

The results from Study 7 have produced a new data set for bathymetry, which is being used by Okanagan communities for flood mitigation planning. While there is no official monitoring mechanism, the Plan of Study acknowledges that as studies are completed, new gaps and/or knowledge will emerge. This might require re-evaluation of previous studies to reflect current knowledge. Challenges with the Plan of Study include securing adequate funding to conduct all 18 studies and handling current lake level management while the study is being completed.

Next Steps

Next steps include continuing to complete the remaining studies according to the 7-year plan and re-evaluating completed studies as new gaps or knowledge arise. Additionally, from the Floodplain mapping report it was recommended that the analysis needs to be reviewed and updated in 10-15 years.

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