This technical memorandum details the development and results of a 2-dimensional (2D) hydraulic model for a ~4.2-mile reach of Quassaick Creek in Newburgh, NY. The primary objective of the study was to simulate existing conditions and 10% conceptual design scenarios to evaluate flood risks and the hydraulic effects of dam removals, channel restoration, and flood mitigation strategies. Key 10% design model scenarios included:

1. Dam Removals: Targeting the Muchattoes Lake, Walsh Road, and Holden Dams to restore natural channel geometry. This involved recontouring both the channel and impoundment areas to reestablish natural flow pathways.
2. Flood Mitigation Infrastructure: Installing a floodwall to protect vulnerable areas, particularly the Mullin Apartments complex, from flooding during large storm events.
3. Rainy-Day Dam Breach Analysis: Modeling a hypothetical breach of the Muchattoes Lake Dam coinciding with the peak of a 100-year storm event to assess potential downstream impacts. The hypothetical removal of these dams and implementation of flood mitigation measures were designed to achieve multiple objectives: restoring natural hydrologic and sediment regimes, improving habitat connectivity for migratory aquatic species, mitigating flood risks for upstream and downstream communities, and addressing environmental justice concerns in flood-prone areas. The dam breach analysis was carried out to assess flood hazards associated with a catastrophic dam failure under existing conditions.