Riparian reforestation and channel change: How long does it take?

Repeated measurements of two small streams in northeastern Vermont document change in channel width and suggest variable rates of widening because of passive reforestation over four decades. Historic data on channel width are available for several tributaries to Sleepers River in Danville, VT, USA from the 1960s. In 2004 and 2008, we re-measured channel dimensions in two of these tributaries, in two reaches of upper Pope Brook and along seven reaches of an unnamed tributary (W12). Four reaches had reforested since 1966; two reaches remained nonforested. The other three reaches have been forested since at least the 1940s. Comparisons between 1966 and 2004 showed that reforested reaches widened significantly, and comparisons between 2004 and 2008 showed continued widening, but at a greater rate. Between 1966 and 2004, reforested reaches widened at an average rate of 4.1 cm/year, while the rate more than doubled for the last four years (8.7 cm/year). Additionally, turbulence data collected during five peak flows in the spring of 2005 showed significantly greater turbulent kinetic energy (TKE) in the reforested reach than in either the forested or nonforested reach. Our data add supporting information to the conceptual model of stream W12 that describes a process of incision, widening, and recovery of a stream reach transitioning from nonforested to forested riparian vegetation.