Claire Leonard
Geomorphology Project
10/26/2005
Containment of a stream near Oakledge Park, Burlington, Vermont
Abstract:
An aerial photograph from 1937, when Oakledge Park in Burlington, Vermont, was a resort, shows a small, unnamed stream discharging into Lake Champlain at the northern edge of the property. A photograph from 1999 shows this stream to have almost completely vanished. Roughly 80 meters of the stream, running through a small floodplain between Flynn Avenue and the lake, remains undisturbed. This small alluvial channel measures between one and two meters in width in most places, with a few wider pools. For the most part, the channel is wider and relatively shallow (~10 cm deep). The channel is constrained largely by living tree roots and woody debris, and appears to change course frequently. The rest of the water from the watershed appears to be contained in three small ponds created as part of the landscaping for a nearby housing development. A small, marshy ditch draining into an underground pipe is the only other remaining evidence of this stream. The stream no longer appears in aerial photographs because it is almost completely contained in ponds or routed underground.
The photographs:
The 1937 aerial photograph shows what was the northern part of the property of
Oakledge Manor Resort. Flynn Avenue runs east-west across the center of this photograph, crossing train tracks and passing by a refinery to the north before ending almost at the shore of Lake Champlain. A smaller road runs to the left bottom corner of the photograph, where Oakledge Manor is located. The intersection of Flynn and the
Oakledge Manor road lies in a wedge of wooded land. The lake here forms a small cove, with an apparently sandy shore. The wedge of trees is located at the southwestern edge of the cove. Extending across Flynn Avenue, and then meandering off to the east is a line of darker vegetation than the surrounding fields. Though an actual stream channel is not

visible, the meandering shape of the vegetation and darker color compared to the surrounding fields indicates a waterway. The obvious stream channel truncates at the railroad track on one end, and appears to discharge into the lake where the trees are in the southern portion of the cove. On the other side of the train tracks are buildings. Some forested areas are visible, mostly in the lower portion of the photograph. Some apparently industrial structures are located near the stream where the waterway turns southward. The shape of the channel meanders to a degree that suggests it has not been drastically altered by humans, except perhaps at the railroad end. The darker vegetation around the stream appears to be smaller than the trees, indicating that it might be marsh.
While the area north of Flynn Avenue in the photograph, and to the east of the railroad tracks, appears to be used for industrial purposes, south of the street appears to be mostly agricultural fields. Some buildings are visible, including the main manor, what looks to be a barn, and a line of cottages, and several roads link these structures to Flynn
Avenue. Though the area has been cleared, the shape of the stream channel indicates that the topography of the area has not been drastically altered.
In a 1999 aerial photo, the wedge of trees north of Flynn Avenue near the lake is still present, but that is the only part of the stream course that appears relatively undisturbed. South of Flynn Avenue, it is impossible to tell that a stream/marsh once meandered there. The portion where the stream was near the railroad tracks is wooded, with a marshy-looking field lying between it and Flynn Avenue (a 1988 aerial photograph shows a square pond in this field). Immediately south of Flynn Avenue is a series of new roads—Forest Lake Dr. and Oakbeach Dr., lined by townhouses. Three ponds are visible in what would have been the stream’s watershed. Two of these lie on either side of a road into one of the subdivisions, Both are roughly rectangular, with the one west of the road being larger than the one east. A third pond occurs south of these, in the same housing development, and is oblong. To the west of the largest pond, bordered by Flynn Avenue and Oakbeach Dr., is an area that looks undeveloped. The northern part of it is wooded, but a wedge going from east to west and ending at the intersection of
Flynn and Oakbeach Dr. has smaller vegetation, and appears to have water in it—perhaps a marsh.

Question: the stream is visible in the 1937 photograph but not the modern one. How has the channel been altered in the intervening time, and where did the stream go?
Field Observations:
The stream discharges into the lake at a sandy beach. A culvert takes the stream under the bikepath, with pools forming on both the beach and the woods sides. Before going under the bikepath, the stream runs roughly 80 m through a triangular section of woods. The stream here is divided into a series of pools and riffles, with a knickpoint with a vertical drop of nearly a meter. In most places the stream measures between one and two meters in width, with a few larger pools or narrower riffles (including the large drop). The banks are not well-defined in the southern portion of the wedge—in places, trees grow directly in the stream, or immediately on the bank. Some riffles flow over topography identical to that of the surrounding woods, with no discernable bank. The bank seems better established along the lower portion of the stream, but remains only about 30 cm high. Roots and woody debris determine the locations of pools and riffles.
No bedrock is visible, and the meanderings of the stream appear to be determined by the vegetation. The entire triangular patch of woods appears to be a floodplain, with evident older channels where sediment is eroded away from tree roots. After an extended period of above average rainfall, several low points on the floodplain contain standing water. At the sampling site is a small bar with fine gravel on it. In stagnant pools in one of the old channels, a film of mineral oil—probably iron or manganese-based—is visible.
As the land is city parkland, digging a large-scale soil pit seemed like a poor idea, but a small soil pit was manageable. The surface of the bank, the O-layer, consists of very dark brown material, rich in organics and full of moss and worm holes. 2 cm down, the soil becomes lighter and sandy, indicating an A-Horizon. This material contains some clay and is cohesive, but is mostly a mix of fine-grained sand and silt. This continues for 2 cm before grading into a larger B-Horizon. This layer consists mostly of clay, with some sand and silt inclusion. The clay is reddish (oxidized) toward the top of the layer, but grades into grey. This goes down at least 15 cm. Some small pieces of poorly-sorted gravel are visible on the bed of the stream, but do not form a distinct layer

in the bank (unless it is farther down). The oxidized clay appears on the surface in some of the dry channels and low places in the floodplain, and may be the source of the oil.
At higher elevation in the woods, the banks become muddy and marshy. The undisturbed section of the stream begins in a culvert going under Flynn Avenue.
On the south side of Flynn Avenue, the stream remains underground in a culvert that vanishes into what appears to be a manmade bank upon which a house (from the
Southwind development) sits. Soon after the stream vanishes, Oakbeach Dr. extends off
Flynn Avenue toward the south. Several housing developments branch out from this street. At the intersection with Flynn is a small wooded area. A manmade ditch extending from this area up the street appears to have marsh and some running water at the bottom of it, which vanishes into a drain. The bottom of this channel, the marshy area, extends six or seven meters, narrowing to three and then two meters as the ditch goes up a small hill.
Further exploration reveals that the “Forest Lake” development, a grouping of townhouses, backs up onto this ditch. The road leading into the development divides two manmade ponds. The ponds are connected by a culvert, with the one on the west side of the road almost twice the size of the other. Their combined area is roughly 2700 m 2 . The banks of these ponds are grassy and fenced, obviously artificial. There are several meters of topography difference between the level of the larger pond and the ditch below, from which it is divided by an earthen dam. The ponds appear to be fairly shallow, roughly 1.5 meters deep. Tree stumps emerging from one of the ponds indicate that they have not been at this level for very long. Houses are built right up against the banks of these ponds. Farther up the road, at a higher elevation than the two other ponds, is a third, oblong pond with an area of roughly 1100 m 2 . One of the narrow ends of this pond also backs up against the earthen wall dividing it from the marshy ditch below. This pond appears unconnected to the other two.
The ditch follows the south-leading road for 200 meters before disappearing into another culvert. Woods behind the townhouses in the three developments appear to have some runoff channels in them, but none contain water. Farther east on Flynn Avenue lies

a large (and relatively new-looking) self-storage facility. In even the most recent aerial photograph, this land appears vacant and marshy, but that is no longer the case.
Field Data and calculations:
Location of sampling site: 4924080 N 0641245 E (in the wooded area near outlet at
Oakledge Park).
Measure Value
Width of stream 1.91 m
Depth of stream (deepest) .17 m
Depth of stream (avg)
A (width x depth)
.09 m
.17 m
2
WP (2 x depth + width) 2.15 m
Hydraulic radius R (A/WP) .08 m 2 /m
Velocity
Slope (from topo)
Discharge (Q = A x V)
.11 m/s
.08 m/m
.019 m
3
/s
Manning's n (calc) 0.058
The velocity measurement may be slightly high, and is based on surface velocity.
The high value for Manning’s n can be justified by the degree to which living tree roots and woody debris inhibit the progress of the stream, and also by the small size (the stream is small enough that any woody debris is a large factor in determining flow).
Distances measured with the GPS—the dimensions of the ponds and lengths of remaining stream—may be off by as much as 20 m.
While the area the stream covers does rise fairly steadily uphill from the lake, the topographic relief is not very high, and the slope of the hill does not appear to be naturally very steep. However, large banks have been built where the stream was developed to hold up houses or contain the water. Vegetation serves as the most important factor preventing hillslope erosion. The increase in soil cohesion provided by

roots of trees and smaller plants keeps the stream from incising deeply into the slope.
The channel is determined by tree roots, and places where the channel flows in high water are defined by exposed roots in shallow incisions into the soil. Where the slope has been artificially steepened as part of development, as on the south side of Flynn Avenue and the dams containing the ponds, grass has been planted to prevent hillslope erosion.
Though the artificial banks are quite steep, they do not appear to be especially susceptible to slope failure.
This site, along with the rest of the Champlain Valley and most of New England, was covered by the Laurentide Ice Sheet in the Wisconsinan ice age. When the ice retreated, 13,000 years ago, the ice formed a barrier to the north-draining watershed of
Lake Champlain. As a result, fresh water backed up in the Champlain Valley and elsewhere in Vermont, forming Glacial Lake Vermont. Glacial lake sediments tend to be varved clays, and it is possible that these underlie the later sediment at the Oakledge
Stream. Over time (9000 ya), as the ice retreated farther but the depressed crust had not yet rebounded, the Champlain Valley was connected to the St. Lawrence Seaway and became an estuarine body called the Champlain Sea. Sediments from this period at the site would probably include clays perhaps overlain by sand and silt. The modern Lake
Champlain, too, probably covered the site in the recent past, as the soil at the site consists of organics overlying sandy, beach-like sediment before grading into the lake/sea clays.
In the 1937 photograph, the stream appears to define a meandering area that was left fallow, probably due to its marshy conditions. The surrounding areas were used as fields and industrial sites. By 1962, the oil tanks north of the stream near the railroad tracks had been expanded to cover the much of the headwaters of the stream, and a single square pond was built on the industrial site to contain the water. The stream channel at that time entered the lake slightly farther south than the current outlet. The majority of the stream’s area had not been developed at this time. A 1974 photograph of the area shows larger riparian vegetation but not increased development. By 1988, Oakbeach Dr. and the Southwind housing development had been built, and the oil tanks between the old stream channel and the railroad had been removed. A pond with similar dimensions to the 1962 pond still existed, and drained into a small square pond just east of Lake Forest

Dr. Two other small ponds (or one larger one with a causeway, depending on interpretation) had been created. The southern part of this housing development appears to have been under construction, and the higher elevation oblong pond has been created.
At this time the stream appears to have been split. The main branch, the one that had run roughly east to west, had been contained in the three ponds before draining into a marsh bounded by artificial earthen banks. No drainage from the oblong pond appears evident in the aerial photo from this time. The meanderings of the stream north of Flynn Avenue are particularly evident at this time.
In 1999, the pond on the now-disused oil tank site has vanished. The two ponds on either side of Lake Forest Dr. has been enlarged. The marshy area at the intersection of Flynn and Oakbeach had been left alone, and a drain or culvert installed to carry the stream under Flynn Avenue and onto the little floodplain. There is no real evidence of the stream east of the ponds at this time, though the undeveloped land appears marshy.
The oblong pond to the south is drained along a ditch down Oakbeach Dr that meets up with the other small marsh.
Over time, the stream appears to meander all over the small triangular floodplain north of Flynn Avenue, as alternate channels from the stream now indicate. The stream no longer appears on the aerial photograph because it has been contained in the three ponds and a series of culverts and drains so that houses could be built on the surrounding land.
References cited:
Governor’s Institute of Vermont, 2003. Science and Technology: Oakledge .
Accessed 10/23/2005. Courtesy Paul Bierman. http://www.uvm.edu/giv/2003/summer03/summerwebfolder/summerweb/oakledge/webp ages/mainpage.html.
University of Vermont Landscape Change Project/Governor’s Institute of
Vermont. Oakledge Park History Site . Accessed 10/14/2005. http://www.uvm.edu/oakledge/.

Figure 1: Location of Oakledge Park in southern Burlington, Vermont. Star indicates the place where the current stream emerges from a culvert under Flynn Avenue.

Figure 2: Comparison of aerial photographs of the stream over time.

Figure 3: Comparison of stream channels, marshes, and ponds over time:

Figure 4: The stream as it is now. Undefined banks (above) and channel constrained by vegetation (below).