Graphical representation of flood inundation for NWS flood categories are based on steady state hydraulic modeling of water surface elevations for incremented discharges. Map shows approximate inundation areas for given water surface elevations and should not be used for navigation or permitting or other legal purposes, but strictly as a planning reference tool.
The purpose of a flood forecast inundation map is to communicate flood risk based on best available information at the time of map development. This flood forecast inundation map has been compiled using the best information available and is believed to be accurate; however, its preparation required many assumptions. Actual conditions during a flood event may vary from those modeled in the map, including erosion and sedimentation. The limits of flooding shown should only be used as a guideline for emergency planning and response actions. Actual areas inundated will depend on specific flooding conditions.
The risk of flooding behind flood risk management (FRM) structures (such as levees, floodwalls, closures, etc.) depends on many factors that cannot be entirely predicted in advance. These factors include whether the FRM structure overtops, length of time the structure overtops, and whether the overtopping leads to breach formation.
The mapping is based on ground elevation data from: FEMA Chemung Watershed 2011; PASDA North 2008; County Chemung Watershed 2005; and County Chemung Watershed 2002
Flood Risk Management Structures (red lines) – Shows levee and floodwall systems that reduce the flood risk. The area behind the FRM structures is not shown as being flooded until the structure is over-topped.
Flood Risk Management Risk Area (yellow shaded area) - Shows the area with flood risk reduced by the flood risk management structures
Modeled Flood Extent- 1972 Tropical Storm Agnes (white shaded area/depth grid layer) - Shows a modelled flood inundation based on the peak TS Agnes river flow. This does not show the actual area flooded during TS Agnes. (See project report for more details.)
Note: Dams upstream in the Tioga River Watershed provide some flood mitigation. Inundation maps would not be representative in the case of a dam breach.
Note: Depths shown are only accurate for the land/overbank areas and not within the stream channel itself.
Note: Map layers represent the inundation of the lowest elevation of intersecting road surfaces. Elevated roadways may remain free of inundation.
If you have questions related to the flood risk management/levee projects within NYS contact the NYSDEC Bureau of Flood Protection and Dam Safety at (518) 402-8185.
The National Levee Database can be accessed here.
The project report can be found here.