Transcript Anthropogenic Impact and Geomorphic Recovery on Upper Mill Brook, West Bolton, VT Abstract This project identifies, maps, and interprets the various sediment.

Anthropogenic Impact and Geomorphic Recovery on Upper Mill Brook, West Bolton, VT
Abstract
This project identifies, maps, and interprets the various sediment packages that resulted from the construction of E. N. Colton’s saw and shingle mills on Mill Brook in West Bolton, Vermont. A
timber crib dam was constructed on the Brook between 1849 and 1852, and remained until sometime between 1905 and 1914. The UTM coordinates of 29 survey points were used to map the
relative locations and lateral extents of five major sedimentary features, including the wedge of silt which filled the millpond. Various sedimentary features were identified with a bucket auger in 10
locations and in 5 soil pits, and include glacial till and clays, landslides, alluvial terraces, pond sediments, alluvial fans, and roadworks. Erosion and slope failure increased as forests were harvested
for timber. The sediment flux of the stream dramatically increased, filling the millpond with silt. We calculated the former millpond to contain 11,321.48 m3 of silt. We used historic land use records to
estimate the life span of the dam at a maximum of 65 years. We compared samples of historic pond sediment and modern stream alluvium to calculate a percent compaction value for the pond
sediment wedge. We then used uncompressed volumes of sediment accumulated over known time intervals, both modern and historic, to calculate a modern sediment flux of 0.14 m3/yr and a
historic flux of 524.9 m3/yr. When the dam breached, after the collapse of the lumber industry and abandonment of the mills, the stream incised through the pond sediments and reverted to a highenergy erosional environment. Our field work and observations suggest that Mill Brook has occupied five different channels during the past 100 years. Topography, woody debris dams, landslides,
and periodic flooding events have heavily influenced channel location: especially in 1990 when a large flood altered Mill Brook to its current streambed. Our data and field observations show that the
landscape responded directly to historic human land use activities, the most egregious of which was clearcutting. The great difference in sedimentation rates shows that hillslopes have been
stabilized by the re-growth of forests, and that very little sediment is currently available for transport by the stream. We can infer that the landscape is capable of adjusting to anthropogenic impacts
through rapid geomorphic change.
Land use history from comparison of historic and modern property maps;
stratigraphy and channel migration from field analysis of sediments.
View upstream (east)
from ATV trail at point Q,
showing 4m gorge
carved on July 4th,
1990. Old IP road grade
shown with dotted lines.
Large rotational failure at
‘A’. Pallet bridge in
foreground.
Upper Mill Brook Valley seen from
West Bolton Cemetery, adjacent
to site of Baptist Church. A
panoramic photograph of the
area, taken c. 1900 from the
church steps, documents
deforestation. It is now in the
possession of the VT Army
National Guard and is classified
information.
Large rotational failure at point R
due to groundwater piping
through unconsolidated
glaciolacustrine sediments.
Located south side of present
stream channel. Sawn stumps are
present in a relic soil horizon
beneath the slide.
Cemetery
Church
E.N. Colton
shingle mill, at
survey point O,
c. 2005
Timber crib
dam, at survey
point A, c. 2005
Soil pit U: soil horizons developed
from pond sediment, stream
gravel, and landslide debris
Schematic
interpretation of
geomorphic
response to
human-induced
landscape change
Corey Coutu
Robert Zimmermann
UVM Geology, 2005
The stratigraphy of the area
preserves a record of the
responses of the Mill Brook
area to anthropogenic
influences throughout
history. Diagrams are NOT
to scale…they show relative
sizes and positions of
features, which have been
simplified and stylized. All
are map views looking east,
upstream.