Floodplain mapping of the Chilliwack River, BC

Floodplain mapping of the Chilliwack River, BC

From Vedder Crossing to Slesse Creek

Yihang (Eric) Shi, MLWS 2016

In order to provide effective information to help minimize flood damage in British Columbia, floodplain mapping is critical for the Federal and BC governments to develop policies and strategies for potential flooding events. BC communities that lack up-to-date floodplain maps risk billions of dollars in property damage and even the lives of their citizens when a flood hits. This study focused on the community of Chilliwack, BC and the Chilliwack River, which has historically been subject to recurrent and severe flooding.

Temperature and precipitation extremes have grown in recent years, leading to an increase in flood risks in the watershed, and the floodplain map is nearly 30 years old. Water levels typically rise during the spring and summer as a result of snowmelt, but the historic larger floods have occurred in the fall and winter, brought on by heavy rainfall or rain-on-snow events.

With more current climate data, it is expected that the modelled flood risk areas have changed since the last mapping period; this project’s aims were to update the map for this region using hydraulic analysis (HEC-RAS) and GIS applications (HEC-GeoRAS, ArcMap). This project provides useful information for landowners, governments, and local communities for the development of flood hazard strategies.