INCREMENTAL VOLUMETRIC CALCULATION USING LIDAR AND GIS - A METHODOLOGY FOR PREDICTING FLOOD TRIGGER LEVELS

Ice jams occur annually along the Mohawk River in upstate New York, especially when the progress of the ice is impeded by obstructions to the channel and flood plain. It is critical to know the trigger level of floods caused by ice jam to minimize future flooding hazards. Volumetric calculation of Z-polygons were calculated at increments of 0.1 m elevation from the minimum to maximum levels within the DEMs allowing simulation of water volumes at different flood levels. Flood simulation using Air-LiDAR DEMs allows accurate determination of flood trigger levels for river segments between channel obstructions. The study area comprises three sections (A, B, and C) of the lower Mohawk River starting at the Rail Bridge above the New York State Canal System Lock 9 (E9 Lock), including the B&M Rail Bridge at the Schenectady International (SI) Plant, and ending at the Interstate 890 Bridge. The main area B, between Lock 9 and the SI Plant, is notorious for ice jams, including one that resulted in a major flood on January 25th, 2010. To understand when flooding occurs, flood trigger levels need to be determined. Flood trigger levels of river elevation were found for the sections preceding area A and following area C of the 2010 flood area (area B) to determine the stage elevations at which up stream water builds up due to ice jam and flooding occurs. Beginning from area A, Rail Bridge to Lock 9, the flood trigger level is 72.3 ± 0.1m. This river section, 2.27 km in length, indicates a shallow gradient, suggestive of a U-shaped riverbed, and the water level increased smoothly decreasing the chance of ice jams. In 2010, the flood trigger level for area B is at 70.7 m. At area C, below the B&M Railroad to Interstate 890 Bridge, the flood trigger level is 69.3 ± 0.1m. River sections B and C display a steeper gradient, suggestive of a V-shaped riverbed due to knickpoint erosion deepening the river basin. Flood simulation graphs for areas B and C show channel constraints and could be prone to ice-jams, while area A appears as less possible for future ice jams.