To mitigate flooding from Pratt Creek in downtown Coaticook, a detention basin enclosed by an earthfill dike was constructed with more than 700 m long and 6.5 m high. Coaticook had been repeatedly affected by flooding in its downtown area, notably during the exceptional flood events of 2014 and 2015, which had a significant impact on the local community. Following the assessment of several alternatives, the selected solution includes a reinforced-concrete culvert equipped with an energy dissipation wall, designed to safely convey both normal flows and flood discharges with return periods up to 1-in-100 years. In addition, an emergency gabion spillway was incorporated at the crest of the dike to accommodate larger floods, ranging from 1:100 to 1:1,000 years, while addressing environmental constraints. The construction of the dike and associated control structures was completed within a few months, under a phased schedule tailored to meet environmental requirements and to provide flood protection to the city before the 20222023 winter season. The detention basin was officially inaugurated in September 2023.