Irene’s Anomalous Deposition

•  Depositional layer identified by Be-7 in cores collected following Irene

•  Fine Grained, >95% clay, matched only by Glacial Varve sediments

•  Near Zero Mercury (Hg) levels •  Low Organic material •  High Potassium (K) levels •  High Bulk Density

Above: Shallow core showing the flood deposit layer, extracted 56 days after Irene

Irene layer ~1.5-2 cm

Sediment Discharge from Tropical Storm Irene into Long Island Sound

Ground Penetrating Radar

GPR Transect shown below

Keeney Cove Bathymetry

Historic River channel

Current channel

KC1 Coring site

GPR Seismic analysis of Keeney Cove shows, through changes in lithology, the depth and profile of the Historic Connecticut River Bed as well as the transition to incised glacial varve sediments.

Depth Profiles for KC1 Coring Site

Abstract: The results presented for this sedimentary reconstruction from Keeney Cove, an abandoned cut off meander formed during the spring flood of 1683 or 1692, are from a 550 cm core. The stratigraphic profile begins with varved sediments from Glacial lake Hitchcock overlain by an unconformity designating previous river channel incision into these glacial deposits. Following the sandy river sediment is a gradual change to low energy lake deposits, showing the gradual closing of the upriver inlet into the lake. Inorganic and notably dense deposits frequently interbed the upper mud facies which, coincide with past flood events on the Connecticut. The resultant sedimentation from Irene is apparent within cores collected immediately following the event, with detectable Be-7 found within the sediments.

Typical flood events are characteristic of high grain size deposits, however Irene is uniquely fine grained, >95% clay, matched only by underlying glacial varve sediments. Further distinctive characteristics of Irene are determined through XRF analyses for elemental abundance. Particularly, peak Potassium concentrations that are only matched by the stratigraphically lower glacial sediments. Hg concentrations within the Irene deposit are close to zero, highly contrasting the underlying concentrations of ~270 ppb. The Hg concentrations of other flood deposits will be presented to assess drops in heavy metal concentrations over time. Presented results will include a core transect to determine a spatial analysis of deposition within Keeney Cove. Specific causes for the distinctive sedimentary fingerprint for the Irene flooding will be discussed.

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Geomorphic Evolution of Keeney Cove Quote from website:

“Historian John Warner Barber’s sketch illustrated how radically the Connecticut River has changed its course

over time. The solid line documents the river’s route just below Hartford in the 17th century, while the dashed line delineates the Connecticut’s path in 1836. The

sharp turn in the earlier course formed what became Wethersfield Cove.”

Glacial Lake Hitchcock 15 kya, ‘X’ marks present day Keeney Cove http://hpi.wethersfieldct.com/index.cgi/1146?section=history

 

Current path of the Connecticut River and Keeney Cove (red)

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Hydrologic Time-series, Hartford CT

How Unique was the Depositional Fingerprint of Tropical Storm Irene? A sedimentary reconstruction of Connecticut River flooding from Keeney Cove.

Andrew Fallon1, Jonathan Woodruff1, Brian Yellen1, Laura Kratz1, Anna Martini2, John Gilbert1 1. Department of Geosciences, University of Massachusetts, Amherst, MA, United States. 2. Department of Geology, Amherst College, Amherst, MA, United States

Telephone pole with high water marks for historic floods, next to the Old Lyme Ferry, New London CT

Why Was Irene so Unique? •  Concentrated rainfall •  Dam influence •  Change in land sensitivity •  Preservation •  Local morphologic change

Precipitation Aug27-28, 2011

Site comparison of X-radiographs & Hg Levels Depth Profiles for KC1 Coring Site

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