Fluvial Terraces and Post-Glacial River Incision Along the Farmington and Housatonic Rivers in Southern New England

River terraces are landforms that result from hydraulic responses associated with Quaternary climate and base-level changes, as well as tectonic and geomorphic processes. They can be used to interpret paleo–river levels along longitudinal profiles and assist in revealing the processes of river incision and knickpoint migration. This study uses fill and cut-fill river terraces as markers of river incision to address lithology controls on the transient response of watersheds to baselevel and climatic changes along the Farmington and Housatonic Rivers in Massachusetts and Connecticut. This study utilized Geographic Information System (GIS) to extract longitudinal river profiles and compile datasets for stream terrace elevations. Fieldwork at select sites assisted in understanding the stratigraphy of terrace deposits. Conservative estimates are used to establish paleo-river levels (initial location of the river immediately post-glaciation) and study the spatial distribution of stream terraces for multiple reaches along these rivers in relation to observed bedrock knickpoints. From this, three different knickpoint migration and/or emergence scenarios were constructed through the use of these longitudinal profiles, terrace heights, knickpoints locations and known glacial history. These conceptual models assist in explaining complex slope and incision patterns observed along these rivers. Results from this study show that the Farmington and Housatonic Rivers are in transient adjustment influenced primarily by bedrock legacy rather than base level controls since over the past 18 ka. Their highest, former river levels are aggradation surfaces of glaciofluvial, braided floodplains. Not only can we now better understand the previous shape and elevation of these rivers, but also the significance in bedrock legacy to patterns of incision. This research is fundamental to understanding post-glacial landscape evolution in southern New England, and the methods used here can be easily transferred for use in other deglaciated regions around the world