Sediment Dynamics in the Lower Connecticut River, a Tidal River

CT2011_1What: Study of Sediment Dynamics in the Lower Connecticut River, a Tidal River

When: June 12 to July 9

Where: Wesleyan University, Middletown, CT

Who: Suzanne OConnell (Wesleyan University) and Peter Patton (Wesleyan University)

Project Overview and Goals

River and estuarine transport of sediment is important to many aspects of modern life including, biological habitat, channel navigation, river esthetics and pollution distribution. The lower Connecticut River and estuary offer many opportunities to increase our understanding of sediment transport and deposition and provide answers to these questions.

We’ll be investigating the human impact on the Connecticut estuary were fine grained sediment, often contaminated because of Connecticut and Massachusetts’ industrial legacy, the distribution of the invasive Asian clam, Corbicula fluminea and the native, endangered gastropod, Elimia virginica. We’ll also be investigating basic sedimentary processes that form and maintain bedforms in a tidal environment and how this deposition impacts biota and contaminated sediment.

Geologic Background

CT2011_3The CT River extends from the Canadian border in Quebec, 650 km to Long Island Sound (LIS). It is the longest river in New England and the main source of fresh water (70%) to LIS, one of the nations most productive and utilized water bodies. Almost 400 towns and cities, with a population of approximately 2.3 million lie in its 29,000 km2 (7.2 million acre) watershed. In the northern reaches, were it forms the border between Vermont and New Hampshire, forests dominate the landscape. Most of the CT and MA watershed are urban (Springfield, MA and Hartford, CT) or suburban. Roughly the Nature Conservancy preserves 35,000 acres of the watershed from development, local land trusts and as part of the Silvio Conte National Fish and Wildlife refuge.

The lower Connecticut Rive and estuary was recognized by the International Ramsar Convention as a “wetland of international importance,” one of only 21 such designated wetlands in the U. S. In 1997 it was designated an American Heritage River. Through this waterway flows sediment and pollutants. In response to major floods in 1936 and 1938, sections of the river banks in Connecticut were stabilized and the river location and bathymetry has remained relatively unchanged (Horne and Patton, 1989; Patton and Horne, 1992). A navigational channel is maintained through dredging between Long Island Sound and Hartford.

During the summer of 2010, based on a 2002 bathymetric survey, we proposed to examine the bedforms in the lower CT River and focused on the Glastonbury meanders. These were present during peak flow in the 2002 survey. Maximum velocities in 2002 were 71,000 cfs (2010 m3/s), although at the time of the survey discharge was less than 30,000 cfs. In April 2010 the area was again surveyed in preparation for the summer project. Few bedforms were present. Maximum discharge in 2010 was 100,000 cfs (2832 m3/s) and at the time of the survey, was about 32,000 cfs (900 m3/s). The bedforms were present in the Keck June 2010 survey when discharge had decreased to about 8,000 cfs (220 m3/s). Grab samples in this area recovered mostly sand and gravel. For the average velocities we measured, sand waves would be expected in the April survey and variety of bedforms in the June survey.

In the northernmost bedfield, in the straightest reach, the trough contains pebbles and cobbles overlying glacial clay. This area had bedforms during both 2010 surveys, and it is likely that the sand waves are moving over an armored surface and there is no net deposition. In areas within the meanders, contrary to expectations, the finer sediment was located in the troughs along with coarse organic material such as water soaked logs. Underwater vegetation (Elodea canadensis) was rooted and thriving in some of the troughs.

Potential Student Research Projects

  1. Under what conditions are bedforms created in a tidal river? Integrate side-scan sonar, ADCP velocity and discharge profiles, and sediment analyses (especially grain size) from the lower CT River bedforms to model sediment dynamics.
  2. Does the size of the channel opening between a pond and the Connecticut River impact the sediment accumulation rate? Analyze cores or a transect of cores from Saybrook Pond which has a wide connection with the CT River and North Cove, which has a narrower connection, but both are soundward of Hamburg Cove, which is currently being studied.
  3. Are sedimentation rates in tidal ponds connected directly to Long Island Sound east of the mouth of the Connecticut River also unusually high, as are sedimentation rates in ponds in the lower Connecticut River? This would involve analyzing cores or a transect of cores from Point Pond, Old Lyme, CT.
  4. Where and to what extent has the geomorphology of the Connecticut River and its connected water bodies changed in the past 70 years? Since 1934 Connecticut has conducted aerial photographic surveys of the state. This data set is available free of charge and could be imported into a GIS database to calculate geomorphic changes in changes in tidal ponds and along the CT River.
  5. Preferential location of Corbicula fluminea, a small Asian clam (<5 cm) that has been reported in the CT River since 1990, where it was observed south of Middletown near the CT Yankee Nuclear Power Plant. During 2010, the clams were found in samples throughout the meander region between Hartford and Middletown. They have also been reported in Hartford, CT. For this project we would collect grab samples from Middletown to Long Island Sound and identify the type of substrate, salinity tolerance and abundance of these invasive clams.

Recommended Courses/Prerequisites

Sedimentology, hydrology, geochemistry and GIS are recommended but not required. Scuba experience is a plus.


Students will be housed in wood-frame houses near the Wesleyan campus or in Wesleyan dorms. Kitchen facilities are available and a weekly food stipend will be provided. Days will be spent on the CT River or in laboratories at Wesleyan. Weekends will be free to explore local environments such as the White Mountains of N.H., Boston, MA, the Atlantic coast (Cape Cod, Maine), New York City and the Berkshires of western Massachusetts.