New York Water Science Center
Delhi has experienced severe flooding along the West Branch Delaware River; most notably during January, 1996, June, 2006, and October, 2010, and August, 2011. Emergency responders would benefit from a library of flood-inundation maps that are referenced to the stages recorded at the USGS streamgage upstream from Delhi. By referring to the appropriate map, emergency responders could discern the severity of flooding (depth of water and aerial extent), identify roads that are or will soon be flooded, and make plans for notification or evacuation of residents in harm’s way based on current and near-future flood levels.
Digital flood-inundation maps for a 5 mile reach of the West Branch Delaware River through the Village and part of the Town of Delhi, New York, were created by the U.S. Geological Survey (USGS) in cooperation with the Village of Delhi, the Delaware County Soil and Water Conservation District, and the Delaware County Planning Department. Flood profiles were computed for the stream reach by means of a one-dimensional step-backwater model that had been used to produce the flood insurance rate maps for the most recent flood insurance study for the Town and Village of Delhi. This hydraulic model was used to compute 10 water-surface profiles for flood stages at 1-foot intervals referenced to the USGS streamgage at West Branch Delaware River upstream from Delhi, N.Y. (station number 01421900). The flood stages ranged from 7 feet or near bankfull to 16 feet, which exceeds the stages that correspond to both the estimated 0.2-percent annual-exceedance-probability flood (500-year recurrence interval flood) and the maximum recorded peak flow. The simulated water-surface profiles were then combined with a geographic information system (GIS) digital elevation model, which was derived from Light Detection and Ranging (LiDAR) data to delineate the area flooded at each water level. A map that was produced using this method to delineate the inundated area for the flood that occurred on August 28, 2011 , agreed well with high water marks that had been located in the field using a global positioning system. The flood maps were overlaid on high-resolution, georeferenced, aerial imagery of the study area along with gridded versions of the flood maps from which the depth of water can be obtained.
First posted August 2, 2012
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