LATE PLEISTOCENE AND HOLOCENE STREAM TERRACES OF THE DELAWARE RIVER, NEAR EASTON, PA, MAPPED WITH LIDAR DATA

Stream terraces provide information about the former floodplain elevations and can be used to reconstruct former river profiles. During the Last Glacial Maximum (LGM) glacial ice covered the upper half of the Delaware River basin and a built a prominent outwash train that extends into the lower portion of the basin. During the Late Pleistocene, the LGM outwash train was incised by younger glacial meltwater streams flowing from ice-retreat positions upvalley from the terminal moraine and further deposition and incision occurred during the Holocene forming a series of terraces. The number and location of the stream terraces along with terrace lithology can provide insight into the causes of downcutting and help disentangle outwash terraces formed during deglaciation from those formed by episodes of incision during the Holocene. Terraces studies have successfully been used as climate proxies and environmental change indicators (Clement and Fuller, 2007) and to help show deglaciation and isostatic rebound in a watershed (Bridgeland, 2009).

Terraces in the Delaware River have been mapped in detail using traditional field techniques, north of the Delaware Water Gap (Witte, 2010), and between the Delaware Water Gap and Martins Creek, PA (Ridge, 1983). However, terraces in the middle portion of the system between Martins Creek, PA and Reiglesville, PA have not been carefully mapped and correlated to the terraces upstream. By using the newly available Light Detection and Ranging (Lidar) data from the New Jersey Highlands Council (2007), and Northampton County (PAMAP, 2008), high accuracy digital elevation models (DEMs) of the Delaware River and the riparian corridor have been created and manipulated in order to identify river terraces. DEM derivatives (slope maps, hillshades, and cross profiles) have been created to help delineate the extent of the terraces. Lidar data reveal a minimum of three terraces preserved in the Middle Delaware. These terraces will be tied to published work (Stone, et al, 2002; Witte, 2010; Ridge 1983) in the basin that correlates terrace formation further upstream to climate change and isostatic rebound associated with deglaciation to create a more comprehensive river terrace history for much of the Delaware River.