Senior engineer, Senior Associate Dewberry, Maryland, United States
Abstract Submission: Ice jams are prevalent in the Northern parts of the Unites States. Rivers can develop ice covers during winter; ice-jams can cause significant flooding. Although winter discharges may be lower than the those during the summertime, ice accumulation at constrictions to reduce or totally block conveyance downstream (ice-jam). Ice-jam flooding occurs rapidly resulting in water levels significantly higher than the open-water season (summer flows). Therefore, to estimate the highest likely flood hazards for these streams, ice impacted flow conditions should be analyzed in addition to the open-water season flows. This presentation summarizes the hydrologic and hydraulic analysis methodologies applied to analyze the ice impacted floodplains. If reliable ice-affected stage record is available at a gage, statistical methods can be applied to generate stage-frequency. An indirect approach to estimate ice-impact will also be applied using a hydraulic model that considers the hydraulic and physical properties of river ice. This model uses the ice impacted flow frequency estimates. This presentation summarizes the methodologies recommended by Federal Emergency Management Agency (FEMA) to analyze river ice; floodway development will also be discussed. USACE’s HEC-RAS software is recommended by FEMA to analyze ice-impacted floodplains; HEC-RAS analysis is not extended for the 2D solution. Levees adds another level of complexity to analyze the ice-impacted flood hazards in accordance with FEMA’s guidelines for levee-ed floodplains. The presentation discusses techniques that can be applied to levee-ed floodplains as well as on how 1D-ice-jam analysis results can be reflected in a 2D scheme.
Learning Objectives/Expected Outcome (Optional) : Share the current state of modeling ice-impacted floodplains and its use in generating flood hazard parameters required to generate FEMA's Flood Insurance Study. Limitation imposed by not having ice modeling in USACE HEC-RAS 2D solution. How floodways are made for ice impacted streams.
