Sewerage and Drainage Climate Change Vulnerability and Adaptation Assessment

The Northern Rockies Regional Municipality is carrying out a climate adaptation feasibility study to assess the flooding risks for sanitary sewer and drainage infrastructure in Fort Nelson, British Columbia (pop. 4,831). Fort Nelson is in the sub-arctic climate zone, which has seen a steady trend of warming over the past 40 years. The feasibility study will seek to reduce the vulnerability of the drainage infrastructure to the following climate change impacts: increasing rainfall intensity and rainfall-on-snowmelt flooding events; operations and maintenance costs resulting from freeze-thaw conditions; and inflow and infiltration to the sanitary sewer system from rainfall and snowmelt. The focus of the study will be on optimizing capital investments and selecting appropriate design criteria for sizing drainage system improvements, while avoiding flood damage related to rain-on-snowmelt episodes, as well as clogging of drainage infrastructure with ice. The study will involve a combination of field work and desktop analysis to assess risk at a detailed level in a number of specific locations identified through previous investigations and planning work. A two-dimensional flood surface model with connectivity to the underground drainage system will be built using existing LiDAR data. This model will allow for direct assessment of the runoff behaviour related to potential damage to buildings and drainage infrastructure and will be configured for a range of hydrologic conditions. The field work proposed for the study will validate the baseline assumptions and will improve the modelling inputs. Infiltration testing, topographic surveys to validate the Lidar data and an inventory of the catch basin will be carried out. The field work and modeling will lead into capital planning and a lifecycle cost-benefit analysis of various service levels. This will inform the recommendations for service levels and adjustments to capital and operating plans.From a triple bottom line perspective, the study will have financial benefits including optimization of capital and operational spending on the drainage system, which will reduce lifecycle costs and impacts to taxpayers. The environmental benefits include reducing inflow and infiltration in the sewer system which reduce loading on the wastewater treatment plant. The social benefits include flood protection for homeowners and businesses, which will reduce the damage to private property and mitigate the increasing insurance costs due to flooding.