Historic Ellicott City, Maryland Flooding: Safe and Sound Mitigation Plan

ABSTRACT ONLY - On July 30, 2016 a destructive and historic flash flood hit Ellicott City, Maryland. More than six inches of rain fell in approximately two hours, completely overwhelming the natural streams and drainage structures and sending 6 to 8 feet of water down Main Street in some locations. Roughly 22 months later, on May 27, 2018 another flash flood of similar intensity and duration hit the same area with similar results. Since then significant effort has been put into studying what happened, planning for the future of a resilient Ellicott City, and starting the rebuilding process. These efforts have been both short term as well as long term master planning in nature. In April 2019 the Howard County Executive introduced his Safe and Sound Plan for flood mitigation efforts, which included a combination of five large dry flood mitigation ponds within the Tiber Watershed plus two large water conveyance projects, including a 5,900 linear foot rock tunnel under Ellicott City. Two of the dry flood mitigation ponds are under construction and two more are in design. Howard County is working closely with the Maryland Department of the Environment Dam Safety Division relative to the design, hazard classification determination, and permitting for these ponds. The hazard class determination factors in the size of the ponds and their proximity to downstream infrastructure and existing development. When implemented, the projects proposed by the Safe and Sound Plan will minimize the flooding risk to the public as well as to critical infrastructure due to future large rain events.