HISTORICAL ANALYSIS OF MILL DAMS ALONG RIVERS IN NORTHEASTERN CONNECTICUT

The northeastern US has a long history of damming rivers to support a variety of mill industries that produced grain, wood, and even silk. This study examines six watersheds within the upper Thames River watershed in northeastern Connecticut to better understand the history mill dams through time in this region. The data analysis in this study consisted of: 1) georeferencing historic maps and mapping the location of mill sites in 1811, 1850-1870, and early 20th century; 2) examination of mill dam sites in air photos from 1934-2019; 3) investigation of mill dam sites in LiDAR DEM hillshade and slope maps; and 4) comparison of historic mill dam sites with datasets highlighting the location of dams built in the mid-late 20th century. The important results include: locations and number of dams through time; details from the LiDAR analysis such as presence/absence of a clear dam structure, length, height of dam if present, and evidence of trenching or a raceway; existence of a reservoir/pond in maps or air photos; and when the reservoir pond last existed or if it still exists today. Preliminary results suggest an increase in ponding despite a reduction of mill dams, likely due to 20th century dam construction. Ponds existing to present day at historic mill dam sites tend to be rare, as these sites either never had a large reservoir according to historical analysis or if so, the dam was breached intentionally or by floods. This suggests that although historic mill dams were common, there may not be large amounts of legacy sediment stored along these river corridors.