The Legacy of Historic Mill Dams at Three Sites in Amherst County

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The Legacy of Historic Mill Dams at Three Sites in Amherst County
The Legacy of Historic Mill Dams at Three Sites in Amherst County, Virginia
Sarah Lindemann
Department of Environmental Studies
Sweet Briar College
Sweet Briar, Virginia 24595
1
In recent years there has been a growing interest in research pertaining to dam removal
and the impacts that dams have on rivers. While dams are historically known for providing
benefits to people, in many cases they are now outdated and no longer serve a useful purpose
(American Rivers et al. 1999). Dams and the reservoirs they create can impact water temperature
and other aspects of water quality and the way sediment moves through a stream system.
In 2008, a paper published in the journal Science introduced a different way of thinking
about stream channel morphology relating to the presence of dams. Based on fieldwork in
eastern Pennsylvania, Walter and Merritts (2008) stated that stream processes throughout much
of the eastern U.S. have been affected by the historical damming of streams for use as mill ponds
and by the erosion that occurred after mill dams were breached. They concluded that before the
implementation of mill dams and ponds, streams in the mid-Atlantic area were “small
anabranching channels within extensive vegetated wetlands” (299). Most stream systems in the
region today consist of a single channel that lacks any type of wetland area. In addition to
altering stream morphology, former mill ponds have the potential to affect current water quality
and turbidity levels. Other research has supported the research of Walter and Merritts (2008)
indicating that old mill pond sediments are easily eroded and can affect stream banks and water
quality (Pizzuto and O’Neal 2009, Schenk and Hupp 2009).
This study investigates the legacy of historic mill dams and ponds in Amherst County,
Virginia. The research described in Walter and Merritts (2008) was conducted in southeastern
Pennsylvania, yet they claimed their findings applied to the entire mid-Atlantic region.
Nineteenth-century central Virginia experienced a different land use history than Pennsylvania,
however. Plantation style agriculture was the norm, with less industrialization. As a first step
2
toward a fuller understanding of the impact of historic mill dams in this area,we identified three
historic mill pond sites, measured stratigraphic cross-sections of pond and stream bank sediment,
and examined riffle particle size distribution upstream and downstream of former mill dams in
order to understand the local sedimentation and erosion history.
MILL HISTORY IN VIRGINIA
In the mid-nineteenth century, common country mills in the United States numbered in
the tens of thousands because they were the primary source of mechanized power for milling
grain, sawing lumber, and other industrial activities (Hunter 1979). Virginia ranked third among
the states in 1900 in total number of mills, but 90% of them were grist mills that ground grain for
local use, whereas less than one-third of mills nationally were grist mills (Peterson 1935). Grist
mills were local mills that operated for the purpose of local trade. Mill operators typically
received a portion of the grain as opposed to cash. Merchant mills were larger and regionally
operated on a cash basis, buying up excess grain and selling it as flour.
Most of the mill dams were built on low-order streams that were more manageable
(Merritts et al. 2006). A slower, smaller flow of water was easier to maintain and dam than a
larger unruly river that was more likely to experience heavy flooding. The purpose of a mill dam
was to back up water in a pond and store it for use in turning the mill wheel. The larger the pond,
the more water was stored as potential power for the wheel. A mill race (a shallow ditch)
typically brought the water from the pond to the wheel, and the amount of flow was controlled
by a gate at the head of the race. Mill dams were typically constructed of materials available in
3
the area, such as timber, stone, and soil, and so were frequently washed away in floods (Hunter
1979). This is why few historic dams are still present today.
STUDY SITES AND METHODS
The three study sites are located in Amherst County, Virginia, in the foothills of the Blue
Ridge Mountains (Figure 1). The underlying bedrock in this area consists of metamorphic rocks
of Precambrian and Early Paleozoic age (Rader and Evans 1993). The soil types in this area are
mainly ultisols and inceptisols (USDA-NRCS 2006). Historic land use in this area was primarily
plantations growing tobacco, wheat, corn, and other crops. Today the area is largely forest and
pasture land.
Figure 1. Location of study site
Fletcher Mill was located on Harris Creek near the headwaters where the stream is
second-order (Figure 2A). The mill building and dam are no longer present, but a local resident
indicated that the dam used to be located where High Peak road now crosses the stream (Tom
Burford, personal communication, 2011). A small pond was still present in the 1930s, and the
4
mill likely began operating in the 1840s when it was built by Elijah Fletcher. The sinuosity of
the 500-meter reach upstream from the dam site is 0.86 and 500-meter reach downstream is 0.92.
Land around the site is currently used for cattle pasture and hay fields. Three stratigraphic crosssections upstream of the dam location site were measured at Fletcher Mill; and five pebble
counts were performed, three upstream and two downstream.
Cash Mill was also located on Harris Creek downstream of Fletcher Mill (Figure 2B).
The mill building foundation and the original mill wheel are still visible. The mill was built in
1826 and remained in operation until 1933 when the dam was breached (Lundegard 2001). The
sinuosity of the 500-meter reach upstream from the dam site is 0.60 and 500-meter reach
downstream is 0.92. The reach measured is a fourth-order stream. Land use around the site is
currently rural residential and forest. The remains of the most recent dam are visible. One
stratigraphic cross-section was measured upstream of the dam and another downstream. Stream
bed sediment has a sandy texture and was sampled, dried, and sieved to determine particle size
distribution.
The third site is Galts Mill (Figure 2C), located on Beck Creek, a third-order stream near
its confluence with the James River. The mill building is still present and was constructed in
1813 but has not been used since 1953 (Lundegard 2001). The sinuosity of the 500-meter reach
upstream from the dam site is 0.84. One stratigraphic cross-section was measured at this site
upstream from the remains of a concrete dam, pieces of which were strewn about just
downstream. Evidence of an earlier stone dam is visible about six feet upstream from the
concrete dam pieces. Due to steep topography and soil cover, no other measurable sections were
found.
5
A
B
C
6
Figure 2. A) Fletcher Mill site on the headwaters of Harris Creek. B) Cash Millon Harris
Creek further downstream. C) Galts Mill on Beck Creek near the James River.
Stratigraphic cross-sections of exposed stream banks were measured and examined for
particle size, color, sedimentary structures, and layering. Photographs were taken at each site to
document the section. Samples of selected sediment layers were taken back to the lab and
analyzed for particle size using ASTM method D422 (American Society for Testing and
Materials, 2003). Pebble counts were performed at Fletcher Mill and Galts Mill using the
Wolman 1954 method to measure sediment particle size distribution on riffles upstream and
downstream of the historical dam locations.
RESULTS AND DISCUSSION
Stratigraphic Cross-Sections
The gravel at the base of Fletcher Mill cross-section #1 resembles the gravel-bedded
bottom of the current stream, thus representing a former stream bed later buried by mill pond
sediment (Figures 3,4). Mill pond sediment is represented by the layer of clay at the base of
cross-section #3 and the loam layers near the base of cross-sections #2 and #1. The fine particles
that make up clay and loam are consistent with a slow water, mill pond, depositional
environment. Layers of gravel and sand overlying the mill pond sediment in cross-sections #2
and #3 indicate a return of stream flow conditions, perhaps due to a dam breach. The lack of this
gravel layer in cross-section #1 may simply indicate that the stream channel did not pass through
this location. Above the gravel and loam layers at each cross-section the texture changes to
sandy loam or silt loam, indicative of floodplain conditions, unimpeded by a mill dam. Variation
in texture among the different layers may indicate different flood events over time.
7
6.0 ft
sandy loam
loam
silt loam
silty clay loam
clay
soil
6.0 ft
5.5
5.4
6.0 ft
Floodplain
5.5
4.0
3.4
Floodplain
3.0
4.0
3.9
3.8
3.8
2.4
2.1
Stream
gravel
3.1
2.9
Stream
gravel
1.6
1.1
1.0
Mill
pond
Mill
pond
water level
0 ft
#3
1.2
0 ft
#2
Figure 3. Fletcher Mill stratigraphic cross-sections. Dark gray
sections represent gravel, and light gray sections represent sand.
8
Stream
gravel
0 ft
#1
#3
9
Figure 4. Photos of cross-sections taken at Fletcher mill
#2
#1
The Galts Mill cross section (Figures 5, 6) shows a similar pattern to the Fletcher Mill
cross-sections. The bottom layer of gravel with a sandy clay matrix resembles the current stream
bed, indicating a pre-mill-dam stream. The overlying layers of sandy loam and loam represent
the19th-century mill pond. The presence of a second layer of gravel is indicative of stream flow
and a likely dam breach. Loam overlying the second gravel layer indicates that the mill dam was
re-built and a second mill pond was formed.
7.0 ft
possible dam
6.5
mill pond #2
5.4
stream gravel
4.4
mill pond #1
sandy loam
loam
silt loam
silty clay loam
clay
2.0
1.2
pre-mill stream
0 ft
10
Figure 5. Galts Mill cross-section. Dark gray represents gravel.
Figure 6. Galts Mill cross-section photograph.
11
The cross-section located upstream of the visible dam remnant at Cash Mill includes
many distinct layers (Figure 7A) different in character from much of the sediment observed at
Fletchers Mill and Galts mill. Harris Creek at this site is sand-bedded and this is reflected in the
character of the cross-section sediment. The base of the cross-section is a brown loam similar to
mill pond sediment at the other locations. Atop this layer are a series of sandy loam layers in the
with climbing ripples that closely resemble the current stream bed (Figure 8C). The thick sandy
loam between 3.2 and 4.2 feet implies that the 19th-century dam may have failed and been
rebuilt later, overlying alternating layers of sandy loam and silt loam indicating that depositional
conditions varied over time, perhaps reflecting flood events and delta growth. A similar package
of sandy loam overlain by loam in the upper part of the cross-section may indicate a repetition of
the dam breach and rebuilding at the 20th-century location (Figure 7A). Cross-section #2
resembles the first cross-section in many ways but appears to have been partially homogenized,
lacking stratigraphic detail. The thick layer of silty clay loam at the base of cross-section #2
implies that a dam was present further downstream that trapped fine sediment at that location
(Figure 2B). We did not go far enough downstream to locate the other dam site.
12
11 ft
10.5
9.5
20th-C mill pond
8.5
8.0 ft
8.1
7.6
6.9
19th-C mill pond w/
flood events and
growing delta
6.7
6.2
6.0
5.6
5.6
4.9
19th-C mill pond w/
flood events and
growing delta
4.9
4.5
3.9
4.2
19th-C dam rebuilt
3.2
19th-C dam failure
3.1
2.9
2.2
0.8 - 0.9
0 ft
13
0 ft
Figure 7 (A, B). Cash Millcross-sections. Light grey represents sand.
sandy loam
loam
silt loam
silty clay loam
clay
soil
(A)
(C)
Figure 8.
(A) Cross-section #1
(B) Cross-section #2
(C) Climbing ripples at cross-section #1
14
(B)
Bed Sediment Particle Size
Harris Creek at Cash Mill is sand-bedded with a median particle size just over 0.2 mm,
categorized as fine sand. Riffle pebble counts taken at Fletcher Mill display a unimodal
distribution in the greater than sand sized fraction upstream and a bimodal distribution
downstream (Figure 9A). The mean values downstream are much larger than those upstream, but
the medians do not show the same pattern (Figure 10A). Galts Mill data show a similar particle
size distribution to Fletcher Mill (Figure 9), with upstream counts having a unimodal distribution
while the downstream count displays a bimodal distribution. The downstream median particle
size is higher than those upstream, but the mean has an intermediate value. In both cases, the
peak in size upstream occurs where the trough between modes occurs downstream. Prior
research has shown that dams tend to segregate sediment by size, with larger particles present
downstream of the dam and smaller particles trapped upstream (Williams and Wolman 1984). It
appears that this coarsening of sediment downstream of dams is still observable decades after the
dams have been removed. Further investigation of this phenomenon may have implications for
modern dam removal projects.
15
%
%
25
8-16
8-16
16-32
16-32
64-128
128-256
32-64
64-128
128-256
particle size (mm)
32-64
256-512
256-512
512-1024 1024-2048 2048-4096
512-1024 1024-2048 2048-4096
Upstream 2
Upstream 1
0
5
Figure 9 (A, B) Percentage of sediment particle sizes at Fletcher mill (A) and Galts Mill (B)
particle size (mm)
Downstream 2
Downstream 1
4-8
4-8
Upstream 3
2-4
2-4
10
<2
<2
Downstream 1
Upstream 2
Upstream 1
15
20
25
30
35
0
5
10
15
20
16
(!"
)*+,-./%012/%3445%
'!"
&!"
)*+,-."
)*-."
%!"
$!"
#!"
!"
!"#$%
!"#&%
!"#'%
!"($%
!"(&%
Figure 10 (A). Mean and median particle sizes for Fletcher mill
(!"
()*+,-.%/01.%2334%
'!"
&!"
)*+,-."
)*-."
%!"
$!"
#!"
!"
!"#$%
17
!"#&%
!"'$%
Figure 10 (B). Mean and median particle sizes for Galts Mill
CONCLUSIONS
Careful interpretation of stratigraphic cross-sections can yield a significant amount of
information about the history of mills and streams in different locations. The information
gathered about particle sizes from the pebble counts performed shows that although the dams at
the sites visited were breached decades ago, they have continued to make an impact on current
stream conditions. The sheer amount of sediment backed up by these mill dams is another mark
of their lasting impact. Between 6 to 11 feet of sediment were surveyed at each site, all a result of
deposition caused by mill dams. The agricultural practices of the 19th-century contributed
massive amounts of sediment to streams that became backed up behind mill dams. As the dams
were breached and time passed, these streams have incised anywhere from around 8 to 10 feet
from their highest levels during the 20th century, carrying all of this sediment with them. One
of the questions that still remains regarding Walter and Merritts (2008) study is whether or not
mill dams are largely responsible for the backing up of sediment all over the mid-Atlantic region.
Dams certainly played a role in this, but we are hesitant to say that they were the sole cause of
sediment filled floodplains.
Further research in this area could lead to a greater knowledge base regarding mill dams
and ponds in Virginia and elsewhere. Using GIS to map historic mill locations with the aid of
census records would help locate other historic mills and gather information about their
surrounding areas. This would also allow for more visiting and analysis of mill locations over a
broader area. The use of LIDAR and time sequences of aerial photos to quantify stream bank
18
erosion rates would also prove informative, as been shown in southeastern Pennsylvania and the
Shenandoah Valley of Virginia.
REFERENCES
American Rivers, Friends of the Earth, and Trout Unlimited (1999) Dam Removal Success
Stories.
American Society of Testing and Materials. (2003) Annual book of ASTM standards. ASTM
International, West Conshohocken, PA.
Hunter, L. C. (1979) Waterpower: A History of Industrial Power in the United States, 1780 1930. Charlottesville, VA: University Press.
Lundegard, M. (2001) Mills and mill sites of Amherst, Campbell, and Lynchburg counties,
Virginia. Friends of Colvin Run Mill.
Merritts D.M., Walter R., Rahnis, M., Heister, K., Fraley, L., Miller, A., Oberholtzer, W. (2006)
Buried Holocene streams and legacy sediment: Late Pleistocene to historical changes in stream
form and process and implications for stream restoration, Mid-Atlantic Piedmont region.
Geological Society of America Annual Meeting Field Trip guidebook.
Peterson, A.G. (1935) Flour and grist milling in Virginia: a brief history. The Virginia Magazine
of History and Biography, vol. 43, p. 97-108.
Pizzuto, J. and O’Neal, M. (2009) Increased mid-twentieth century riverbank erosion rates
related to the demise of mill dams, South River, Virginia. Geology, vol. 37, p. 19-22.
Rader, E.K. and Evans, N.H. (1993) Geologic Map of Virginia—Expanded Explanation. Virginia
Division of Mineral Resources, Charlottesville, VA.
Schenk, E. R. and Hupp, C. R. (2009) Legacy effects of colonial millponds on floodplain
sedimentation, bank erosion, and channel morphology, mid-atlantic, USA. Journal of the
American Water Resources Association, vol. 45, 597-606.
Walter, R. C. and Merritts, D. J. (2008) Natural streams and the legacy of water-powered mills.
Science, vol. 319, p. 299-304.
Williams, G. P. and Wolman, M. G. (1984) Downstream effects of dams on alluvial rivers. U.S.
Geological Survey Professional Paper 1286.
Wolman, M. G. (1954) A method of sampling coarse river bed material. Transactions of
American Geophysical Union 35, p. 951-956. 19
19
APPENDIX
Hydrometer percentages for sample sediment layers:
Soil Texture
% sand:
% silt:
% clay (<3.9um):
FMU-3A (brown
clay, pond sed.?)
clay
18%
42%
40%
CMU-1A (sandy
clay w/
laminations)
loam
28%
46%
26%
GMU-1D (loam)
loam
32%
46%
22%
FMU-2A (gray
clay)
loam
43%
39%
18%
FM-1B (clayey
silt, pond
sediment?)
loam
45%
41%
14%
GMU-1B (sandy
clay, finer sand)
loam
50%
30%
20%
GMU-1C (sandy
clay w/gravel
clasts)
loam
52%
29%
19%
CMD-2
Streambed
sand
92%
4%
4%
GMU-1A (sandy
clay)
sandy loam
54%
27%
19%
FM-1C (reddish
brown sandy
loam)
sandy loam
54%
33%
13%
CMD-2C
sandy loam
55%
28%
17%
FMU-3C
(floodplain sed.)
sandy loam
57%
34%
9%
CMU-1B (sand w/
climbing ripples)
sandy loam
60%
28%
12%
FM-1E
(floodplain sed.)
sandy loam
62%
29%
10%
20
FMU-2C
(floodplain sed.)
sandy loam
65%
23%
12%
CMU-1D (sand
sandy loam
76%
13%
11%
FMU-3B (clayey
sand)
sandy loam
52%
38%
10%
CMU-1E (light
colored clay)
silt loam
16%
59%
25%
CMU-1C (clay)
silt loam
20%
53%
27%
FMU-3D (clayey
sand, smooth)
silt loam
20%
59%
21%
FM-1D (reddish
brown silty clay)
silt loam
31%
53%
16%
CMD-2A
silty clay loam
19%
47%
34%
21
Sieving data:
Particle Size
Percent
Particle Size
Particle Size
(mm)
FM-1A
FMU-2B
CMD-2B
CMU-1
silt
0.003
2.53
1.71
3.19
0.50
very fine sand
0.0625
2.73
2.12
4.48
1.16
fine sand
0.125
9.61
17.45
13.36
12.13
medium sand
0.25
19.02
36.31
21.59
48.95
coarse sand
0.5
17.46
18.68
25.51
29.74
very coarse sand
1
12.80
9.16
23.30
6.98
granule
2
9.77
4.79
7.38
0.52
pebble
4
26.07
9.78
1.19
0.03
100.00
100.00
100
100
total percent
22
23
<2
2-4
4-8
8-16
16-32
32-64
64-128
128-256
256-512
512-1024
1024-2048
2048-4096
very fine
gravel
fine gravel
medium
gravel
coarse
gravel
very
coarse
gravel
small
cobble
large
cobble
small
boulder
medium
boulder
large
boulder
very large
boulder
Size Range
sand
Size Class
0.0
0.0
0.0
0.0
0.9
1.9
10.3
22.4
21.5
17.8
4.7
20.6
FMU 1
0.0
0.0
0.0
0.0
0.9
7.4
23.1
27.8
0.0
0.0
0.0
0.0
0.0
8.8
27.2
33.3
9.6
11.4
13.0
16.7
0.9
8.8
FMU3
3.7
7.4
FMU2
0.0
0.0
0.0
4.0
16.0
16.0
12.0
16.0
14.0
9.0
0.0
13.0
FMD1
0.0
0.0
0.0
1.7
18.3
10.8
7.5
11.7
18.3
0.0
0.0
0.0
11.2
9.2
7.1
7.1
21.4
22.4
8.2
2.0
1.7
15.0
11.2
GMU1
15.0
FMD2
0.0
0.0
0.0
3.7
9.2
8.3
20.2
22.9
22.9
8.3
0.0
4.6
GMU2
0.0
0.0
0.0
0.0
13.3
15.2
21.0
8.6
9.5
16.2
11.4
4.8
GMD1
Pebble Count Data:
24

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