Gravel Extraction in Alluvial Rivers

Gravel Extraction as a Historical Economic Industry and its Morphological Effects on the West Branch of the Little

River, Stowe, VermontErin Turner

Geography 246November 18, 2004

Mountain Rd

Cape Cod Rd

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• Link changes in channel morphology of the west branch of the Little River to gravel extraction by:– Observing two time periods (1962 and 2000).– Determining profile, sinuosity, area, and

width of the channel for each time period.– Determining presence and area of gravel

bars for each time period.– Obtaining historical information about gravel

extraction amounts.

Objective

• Digitized gravel bars-calculated areas.• Digitized and calculated stream lengths,

measured valley length - sinuosity.• Digitized data collection points (10) -

measured stream width for both years, measured how far each bank had migrated over time.

• Looked at historical records of gravel extraction (1980-1986).

Methods•Digital orthophotos (2000) and aerial photos (1962) - georeferenced.•Digitized the stream channels for both years-calculated areas.

ResultsDigitized stream channels for 1962 and 2000

ResultsDigitized gravel bars: 1962 and 2000

Results

•1962: larger area, shorter length, moderate meanders, less gravel bars, smaller area of gravel bars.

Digitized lengths, calculated areas of river and gravel bars, and calculated sinuosity

1962 2000 River Area (m2) 85,005 66,963 River Length (m) 4,469 4,773 Sinuosity (river length/valley length)

1.46 moderate meanders 1.55 pronounced meanders

Number of Gravel bars 16 20 Area of Gravel bars (m2) 24,704 55,431

Results

Digitized data points

XY

XY

XYXY

XYXY

XY XYXY XY

9876

5

4

3

2

1

0

ResultsRiver Widths: 1962 and 2000

0

10

20

30

40

50

60

70

80

Data points

Wid

th (

m)

1962 River Widths (m) 2000 River Widths (m)

Table 1: This table shows the difference in channel width between the years 1962 to 2000. Width is represented in meters and each cluster of data represents a data point collection location. Notice the channel is generally wider in 1962.

Measured widths and shift of the channels at the data point locations

Data Points 1962 River Widths (m)

2000 River Widths (m)

Shift of Left Bank (m)

Shift of Right Bank (m)

0 16.5 15.9 15.1 L 15.5 L 1 10.1 10.6 38.3 L 37.9 L 2 17.6 8.5 51.4 L 59.3 L 3 13.5 8.7 4.4 L 9.4 L 4 44.8 17.2 21.8 L 49.0 L 5 18.2 8.7 63.0 R 53.1 R 6 37.5 16.1 0 none 21.5 L 7 14.5 12.2 34.2 R 31.7 R 8 19.5 8.7 48.5 L 56.6 R 9 69.9 13.2 47.5 R 9.1 L

Conclusions•There was obvious channel change between 1962 and 2000.•Can not attribute change to gravel extraction alone because…..

•Vertical channel change was not measured.•Role of other contributing factors including deforestation, development, or other stream alterations not considered.•Limited time period analyzed.

Coming Soon…

•Gravel extraction amounts: 1980-1986.

•What does it all mean?•A paper synthesizing all of my findings and discussing results.

•Continued research into next semester…