STUDY OF CHANNEL MIGRATION IN A MATURE MEANDERING RIVER - THE SANDY RIVER, WESTERN MAINE

The Sandy River, a tributary of the Kennebec River, is located in Western Maine. Renewed controversy has arisen over gravel removal from the river. Both the Department of Environmental Protection (DEP) and the Maine Geologic Survey (MGS) have initiated studies of the river as a system. The project reported here was primarily funded by the MGS with additional funding from the University of Maine at Farmington and aimed to further understand the dynamic nature of the Sandy River, with particular interest in bar aggradation and degradation. The long term objective of this research is to gain an understanding of the temporal and spatial evolution of the river at the designated sites. Rates of change (migration) can then be compared to historical migration rates determined through aerial photography, and can also be compared as a base line to future changes in the river morphology.

Data collection was conducted during the summer of 2002. Benchmarks were established and detailed initial surveys of five bars were conducted in a stretch of the Sandy River extending from Avon to Farmington Falls. The area of study ranges in Rosgen’s (1996) classification from C-3 to C-5, with gravel and cobbles dominating the northern reaches and sand the southern. Historical migration patterns were derived through interpretation of both aerial photographs, from 1951 - 2002, as well as with modern on-site Total Station surveying and GPS techniques. A detailed topographic map for each of the sites was produced using Foresight software. Aerial photographs were compared using ArcView’s Image Analysis software.

It was determined that the river has altered its course significantly in the majority of these areas. The results, from aerial photographs, are constrained to movement of the river over decades, rather than each year. Future surveys will allow for quantitative results over a much shorter time interval. Surveys from different years can be tied together through the global positions of permanent monuments placed near each bar. A firm understanding of channel migration will allow for informed decision making regarding human intervention on the river system.