The Town of Princeton continues to recover from the November 2021 atmospheric river event and rebuilding from its impacts. The flood caused significant damage, including the destruction of key utility river crossings (water, sanitary, and gas), contamination of water supply wells, erosion of dikes and access roads, and compromising the primary sanitary lift station serving the entire community._x000D_ _x000D_ In response, the town has undertaken various recovery actions such as drilling new pipe crossings, repairing dike sections, and establishing new supply wells, all while considering the uncertainty associated with climate change. Historically, Princeton's rivers have been dominated by snowmelt events. However, current climate change predictions suggest that freshets will occur earlier and decrease in magnitude, while extreme rainfall events will increase both in magnitude and frequency, dictating the flood regime. Estimates indicate that the magnitude of extreme rainfall events could increase flood flows by 80% to 100% with a tremendous amount of uncertainty._x000D_ _x000D_ Consequently, the community is engaged in a comprehensive reimagining of Princeton’s future. This includes evaluating options to restore natural river areas and enhance conveyance capacity, taking an adaptive management approach, adopting floodplain retreat strategies, setting back dikes, and embracing a “planning to get wet” approach to future community planning and infrastructure development._x000D_
The lower Fraser River floodplain in BC has a complex diking system, comprised of 58 dikes, which protects more than 340,000 people living on the floodplain. When it comes to preparing mapping, for planning and emergency response and to support regulation of land use and development, assumptions tied to future upgrading of dikes and the performance of dikes during a large flood event can be critical. _x000D_ _x000D_ Northwest Hydraulic Consultants (NHC) recently completed regional hydraulic modelling and mapping for a 100 km reach of the lower Fraser River. We will discuss the dike performance assumptions selected for the project and the reasoning behind the approach. We will go over the modelling and mapping implications and limitations of the selected approach. Finally, we will share information about the results and potential uses of the new flood maps; as well as challenges, opportunities and lessons learned._x000D_
British Columbia’s hydrologic and climatic landscape is both diverse and complex, encompassing everything from small coastal watersheds to large, snowmelt dominated basins. This diversity presents unique challenges to floodplain mapping projects when it comes to incorporating climate change into the project. _x000D_ _x000D_ In this talk, NHC will share lessons learned from our experience incorporating climate change assessments into open water, ice jam and lake/coastal floodplain mapping projects. We will discuss the idea that the approach to incorporating climate change into a floodplain mapping study is dependent not only on the specific characteristics and climate projections for the watershed of interest but also on various project-specific factors, and that a single approach can rarely be applied to multiple studies. _x000D_ _x000D_ Drawing on our range of experience, we will demonstrate how a tailored approach to climate change is essential for successful implementation in floodplain mapping. Additionally, we will explore common challenges, such as the availability of data and tools, navigating the regulatory environment, and project planning and budget, and how these play into determining the approach and methodology of climate change analysis for floodplain mapping studies. Finally, we will discuss ways that we can move forward from some of these challenges and constraints to provide better mapping products in the future. _x000D_
Floodplain maps are important tools to help First Nations and local governments make informed decisions related to land use, emergency preparedness and flood response. Detailed floodplain maps are currently in progress for the Nicola and Coldwater Rivers in Central British Columbia (BC) as part of the Provincially and Federally funded Flood Hazard Identification and Mapping Program (FHIMP). These rivers flow through the City of Merritt and several Nlaka’pamux and Syilx First Nations communities, including Nooaitch, Cook’s Ferry, Shackan, Upper and Lower Nicola, and Coldwater Indian Bands. Many of these communities were significantly impacted by the November 2021 atmospheric river (AR) flood event. Incorporating the traditional knowledge and experiences of communities that lived through recent extreme events is an important part of the study. As well, sharing of resources across the Nicola Valley watershed, often through data sharing agreements, on items such as bathymetric surveys, hydrologic and climate change analyses, hydraulic modelling, lidar and orthoimagery acquisition and quantitative analyses of geomorphic change significantly improved the study outcomes. Collaboration with other practitioners and decision makers in the watersheds helped in the development of high-quality, standardized and consistent floodplain maps and advanced a shared source of flood-related knowledge in the watersheds.
