Preliminary Flood Hazard Assessment for Ignace and South Bruce Study Areas

Abstract

Recently the Nuclear Waste Management Organization (NWMO) carried out a preliminary flood hazard assessment for the Wabigoon Lake Ojibway Nation (WLON)-Ignace and Saugeen Ojibway Nation (SON)-South Bruce areas. The assessment was based on current existing natural conditions, without the assumption of any future development or landscape grading. In this study, probable maximum flood levels due to extreme precipitation events (including both direct rainfall on-site and rainfall on upstream catchments) were derived for these two study areas with two commonly used computer programs, HEC-HMS (hydrological model) and HEC-RAS (hydraulic model). This study considers multiple probable maximum precipitation (PMP) scenarios for three periods with three climate change risk projections. Results of the watershed-scale simulations suggest that, under extreme precipitation conditions, the flood risk for the WLON-Ignace area is small, with surface ponding due to rainfall being the primary risk. For the SON-South Bruce area, flood risk exists from both surface ponding and flooding along the Teeswater River. By adequately designing the future site stormwater management measures and taking into consideration the floodplain boundaries with respect to the site layout configuration, surface flooding impacts can be mitigated.