DOCUMENTING 20TH CENTURY CHANGES IN RIVER MORPHOLOGY USING AERIAL PHOTOGRAPHS AND FIELD SURVEYS: NARRAGUAGUS AND SHEEPSCOT RIVERS, MAINE

Over the past few centuries the population of Atlantic salmon has decreased in New England. This decrease is attributed largely to over-fishing and alteration of natural fluvial habitat by logging and other land-use changes. The Narraguagus River is located in downeast Maine, and the Sheepscot River is located in midcoastal Maine. These systems are of interest because they are two of eight rivers left in Maine with remnant wild Atlantic salmon populations, identified under the federal Endangered Species Act as a distinct population segment. These rivers are now being investigated by land managers and watershed non-profit groups for possible habitat restoration. We evaluate the effects of land-use changes on channel morphology and habitat through field and aerial-photograph analysis in order to investigate the trajectory of channel response in the region. We focus on measurements of channel width and sinuosity because these (1) can change over short timescales, (2) influence water flow and sediment transport processes, and (3) therefore bear directly on fish habitat quality and restoration. First, we evaluate our remote-sensing methods through quantitative comparisons of channel bankfull width measured at 100-m intervals along 3-5 km reaches of the Sheepscot and Narraguaguas Rivers with similar measurements made from recent orthorectified and georeferenced aerial photographs using geographic information systems. Next, we document changes in channel width and sinuosity since approximately 1940 using a time series of aerial photographs. Finally, we compare morphologic changes with changes in land-use patterns.