THE ENVIRONMENTAL LEGACY OF CHANNELIZATION ON AQUATIC HABITATS OF A GRAVEL-BED WANDERING RIVER

As one of the last remaining cold-water fisheries in Massachusetts, efforts are underway to restore the natural functioning of the gravel-bed, wandering Hoosic River. Channelisation of kilometres of stream peaked into the mid-20th century, resulting in narrowed stretches of channel absent of any alluvial cover. The environmental impacts of this extensive engineering have not been thoroughly evaluated, but are motivating several plans for enhancing ecological flows and channel connectivity. In order to better assess the environmental legacy of channelisation and to inform restoration strategies being developed, we document the historical changes to the river’s planform and aquatic habitats and assess the conditions needed to support stable bed-material supplies. Using maps and historical aerial imagery, we highlight the historical importance of mid-channel bars and point bars to the previously unaltered stream. We quantify the rate of loss of these in-channel features as a result of channelisation and supplement the historical analysis with modern surveys of the channel. We conclude that the sinuous, meandering planform that is the focus of many of the restoration plans may be inappropriate for the Hoosic River, as its flashy discharge and unsteady bed-material supply has tended to force the formation of large mid-channel bar habitat that creates temporally stable bifurcations.