The Delaware Floodplain
Introduction
Situated on the Delmarva Peninsula between the Delaware and Chesapeake bays, Delaware is the lowest state in the USA with a mean elevation of just 60 feet above sea level.  Vulnerable to flooding from rising sea levels and ocean-fueled tropical storm systems, coastal Delaware is one of only three states on a peninsula surrounded on three sides by water.  Delaware floods originate along the hilly, rocky Piedmont streams in northern New Castle County and from tidal influences along the bay and Atlantic Ocean.
 
100-year Floodplain
Over 331 square miles or 17% of Delaware’s land mass are within a mapped 100-year floodplain.  The distribution of floodplains in all three Delaware counties is similar ranging from 16% to 18% of the land.
 
                                      100-yr Floodplain (sq mi)     % of County
New Castle County                         67                              16%
Kent County                                  94                              16%
Sussex County                             170                             18%
 
Road Miles in Floodplain
Approximately 621 road miles are in the 100-yr floodplain in Delaware.  New Castle, Kent, and Sussex counties have 128, 75, and 418 road miles in the 100-yr floodplain, respectively.  Watersheds with the largest mileage of floodplain roads include the Christina River in New Castle County (44 mi), Murderkill in Kent County (16 mi), and Indian River Bay (106 mi).
 
Structures in Floodplain
Over 18,000 structures are in the 100-yr floodplain in Delaware with 2,431 structures in New Castle County, 1,853 structures in Kent County, and 13,760 structures in Sussex County.  Watersheds with the most structures in the 100-yr floodplain include the Christina River in New Castle County (1,007 structures), St. Jones River in Kent County (567 structures), and Indian River Bay (3,856 structures).
 
Flood Discharge
Watersheds with the most extreme floods (highest 100-yr flow per sq mi) include Shellpot Creek in New Castle County (1,161 cfs per sq mi), Duck Creek (Smyrna River) in Kent County (327 cfs per sq mi), and Indian River (52 cfs per sq mi).  Some of the largest floods in Delaware have occurred on July 8, 1989 (July 4th storm), September 16, 1999 (Hurricane Floyd), and September 15, 2003 (Tropical Storm Henri).
 
Floodplain Interactive Web Map
This map shows the FEMA 100- and 500-year floodplains floodplains in Delaware, along with relevant base data, such as roads, streams, political boundaries, aerial photography, Water Resource Protection Areas (WRPAs), etc.  Delaware citizens and governments can access the mapping to determine flood insurance, flood warning, and flood response needs.
 
Get the report