The St. Margaret’s Bay (SMB) Hydro system is operated by Nova Scotia Power and is located 20 km west of Halifax. The SMB system compromises 15 dams on seven reservoirs and drains a watershed of 630 km2. Two main rivers flow through the SMB system: the Indian River and Northeast River, with the Little Indian Lake Diversion Structure in between the two.  Power generation within the SMB system is provided by two stations - Mill Lake and Tidewater. The Mill Lake generating station includes the Sandy Lake Plant and the Mill Lake Plant. The total installed capacity of these three plants is 10.4 MW.  In 2009 the dams were classified according to the then newly developed (2007) CDA Dam Safety Guidelines. In the following years, Nova Scotia Power completed several rehabilitation projects to bring the SMB structures into alignment with the Dam Safety Guidelines.  In 2023, Hatch with support from Applied Weather Associates was tasked by Nova Scotia Power to create an updated flood study and dam breach assessment for all the dams in the system and create flood maps for emergency preparedness.  The flood study included a review of the Probable Maximum Precipitation (PMP) for the St. Margaret’s Bay system following a major storm in Nova Scotia in 2023 which caused extensive flooding. As part of this scope, an analysis on the impacts of climate change on the PMP was also completed. The dam break analysis was carried out using a fully 2D HEC-RAS model representing an extensive computational update from the previous dam break study in 2009 using FLDWAV. This paper presents the modelling that was undertaken to update the consequence classification for the dams in the St. Margaret’s Bay system and create dam breach maps for emergency preparedness.