A case study: The impact of the 1962 northeaster on Delaware’s Atlantic coastline

McCarty, Elizabeth
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University of Delaware
The 1962 Northeaster, called by many “The Storm of the Century,” was one of Delaware‟s most devastating coastal storms. It lasted over more than five consecutive, semi-diurnal, perigean spring tidal cycles (Zhang et al., 2002). Maximum winds reached 112.7 km/hr (70 miles/hr), waves were an average of 6-9 m (20-30 ft), and the storm surge reached 2.9 m (10 ft) (Carey & Dalrymple, 2003). Overwash from beaches brought greater than 1.2 m (4 ft) of sand onto the streets, homes, and buildings of communities along the Delaware coastline (Podufaly, 1962). This thesis presents a case study of the impact of the 1962 Northeaster on Delaware‟s Atlantic Coast shoreline. The destructive nature of the storm is quantified using historical aerial photographs, shoreline change data, and Light Detection and Ranging (LiDAR) digital elevation maps. The potential impact of a future storm of this magnitude occurring along Delaware‟s modern shoreline is briefly discussed. Within a Geographic Information System (GIS) framework, georeferenced historic aerial photographs were analyzed for changes in shoreline position, aerial extent of overwash, and number and areas of extensive building damage caused by the storm. For these analyses, the Delaware Atlantic Coastshoreline between Cape Henlopen to the Delaware-Maryland was divided into twelve zones, each approximately 3.7 km (2.3 mi) in length. To quantify erosion due to the storm, the landward displacement of the Delaware shoreline between 1960 (pre-storm) and 1962 (post-storm) was measured at 500 m (1,640 ft) intervals along its length and the maximum amount of landward displacement within each of the zones was determined. The maximum amount of erosion as a result of the storm was 150 m (490 ft) in the zone located within the Delaware Seashore State Park, just north of the Indian River Inlet. Significant amounts (100-130 m (330-430 ft)) of shoreline erosion occurred in the northern portion of Delaware Seashore State Park and near South Bethany and Fenwick Island. The zones with the greatest amounts of maximum erosion as a result of the 1962 Northeaster coincide with the areas of significant longer-term erosion identified by Honeycutt (2003). Areas of overwash due to the storm were digitized on the 1962 post-storm aerial photographs. The total extent of overwash in the study area was 8.34 km2 (3.2 mi2) with the most visibly pronounced areas along the bay barrier portion of the shoreline south of Dewey Beach, Delaware. Maximum and minimum lateral (landward) displacement of overwash sand was measured for each zone. The maximum amount of lateral displacement, ~650 m (2150 ft), was found to be located just south of Bush Island in Delaware Seashore State Park. The least amount of lateral overwash, ~45 m (150 ft), occurred near Rehoboth Beach.Buildings present in the 1960, 1962, and 2002 aerial photographs were digitized as GIS point shapefiles. The 1962 post-storm aerial photographs indicated that the destruction of buildings was highly correlative to the areas of overwash from the storm. As shown by the 2002 aerial photographs, a great deal of residential development took place along the Delaware Atlantic shoreline. For example, in the area of Bethany Beach the increase in structures was as high as 812%. In order to assess the potential effects of another storm of this magnitude on the modern coastline, elevation maps based on LiDAR were used to show areas most at risk due to a 2.9 m (10 ft) storm surge, equivalent to that determined for the 1962 storm. As with the 1962 Northeaster, these high risk areas include the vast majority of the coastline. The effect of 6-9 m (20-30 ft) wave heights, similar to that observed during the 1962 storm, on top of the storm surge was also considered. For example in the areas of greatest development near Bethany Beach, where major overwash and flooding occurred during the 1962 storm, it would be predicted that large-scale erosion of the dune barrier systems with subsequent overwash could occur followed by flooding with levels of inundation approaching 12 m (36 ft). Although modern building codes are much improved from 1962, one could still expect that a future coastal storm of the magnitude of the 1962 Northeaster would have significant impact on Delaware‟s coastal communities.