HISTORIC LEGACY SEDIMENT WITHIN THE CATCHMENT OF SUSQUETONSCUT BROOK, LEBANON, CONNECTICUT

The rural colonial-era town of Lebanon, Connecticut provides an ideal opportunity to examine how the expansion and contraction of the historic farm economy impacted soil, stream and wetland systems. Though the focus of landform change is usually on fieldstone walls, small wetlands were also strongly impacted. More specifically, sediment eroded from upland slopes was retained within low-order catchments, likely creating more wetlands through sediment occlusion and riparian aggradation than were lost through deliberate ditching and excavation.

The relevant advantages of Lebanon as a case study in fluvial sediment transport are: (1) Historic changes in the farm economy follow a pulse-decay model, with human population rising rapidly after 1692, peaking at >3960 in 1774, and declining until the end of America’s Great Depression. (2) Land disturbance can be easily constrained within the small, well-defined catchment of Susquetonscut Brook (14 km²), a locally rugged, till-covered landscape with loamy soils, factors that magnified changes in flood hydrology and sediment delivery. (3) A broad range of inland wetland types was originally present, providing many strategic opportunities for stratigraphic and morphological study. (4) Catchment processes there (human and non-human) are representative of those elsewhere in rural southern New England inland from the coast.

Our study is based on: historical archival research; a systematic reconnaissance of stream reaches for human manipulation; a classification of 61 discrete wetlands; a stratigraphic-morphological analysis of 18 representative wetland sites from the larger population; and field-calibrated numerical simulations of flood runoff for pre-settlement and peak-settlement scenarios. We demonstrate that: wetlands were dramatically impacted by a spike of sediment influx leading to paleosol burial and riparian aggradation; the responses of wetlands were individualistic, and governed by their hydrologic settings, and; the pulse of trapped legacy sediment is only slowly being released to larger streams.

Note: This paper updates and re-focuses work published in 1998 (Geological Society of America Reviews in Engineering Geology, Volume XII (C.W. Welby and M.E. Gowan, eds.), p. 23-42) by Robert M. Thorson, Andrew G. Harris, Sandra L. Harris, Robert Gradie III, and Michael W. Lefor (deceased).