Historic channel change on Esopus Creek, upstream of the Ashokan Reservoir, Catskills, New York

An understanding of historic channel change is fundamental to informing good stream management decisions. This study correlated the history of recent channel change on Esopus Creek in the Catskill Mountains of New York to patterns in the hydrologic record in order to understand the role of hydrologic controls on the stream's changing morphology. This study identified dynamic stream segments that have the potential to impact infrastructure and water quality in this watershed, which supplies a significant portion of New York City's drinking water. Changes in channel width, sinuosity, channel index and meander migration were obtained from quantitative analysis of aerial imagery from 1959, 1980 and 2001, along with historic topographic maps and field reconnaissance. Discharge patterns correlated with observed morphologic changes, while the role of other controlling variables such as basin and valley geography, climate, changing land use and historic channelization was explored.While there were no significant net changes in active channel width for the overall study period, overall channel width decreased between 1959 and 1980 and increased between 1980 and 2001. Reach-scale changes in channel width followed the same trend, with most reaches narrowing between 1959 and 1980 and widening between 1980 and 2001. The frequency and timing of large flow events were more significant in producing morphologic changes than the magnitude of a single event. The flood of record in 1980, which followed a 22-year hiatus in large flows, appears to have performed limited channel-width changes, while smaller magnitude but more frequent flows had much greater effects. Furthermore, time periods during which moderate flows, approximating bankfull conditions, occurred more frequently were correlated to periods of channel widening, whereas periods of less frequent moderate flows were correlated to periods of channel narrowing.Overall channel sinuosity did not change significantly over the period of study, although some reaches did change because of meander migration, channel cutoffs and/or avulsion. An increase in channel index for many reaches and for the stream as a whole suggests a trend toward a more strongly anabranching planform.Results of this study suggest that we may expect increased channel widening, through increased bank erosion and side channel activation, as frequent high flows have continued to impact Esopus Creek and are expected to do so in the future. The increased erosion and suspended sediment that accompanies bank erosion into lacustrine sediments will have potentially significant impacts on infrastructure and the New York City water supply.