Waterbury Dam Disturbance Mike Fitzgerald Devin Rowland Abstract The Waterbury Dam was completed in October 1938 as a method of flood control in the Winooski Valley. The construction began in April1935 by the Vermont Civilian Conservation Corps. The dam is an earth built dam with a stone slope for protection totaling 562 meters long by 57 meters high. In June 1953 a hydroelectric plant, the Little River Hydro Station, was installed at the base of the dam. The construction of the dam caused a pool of water to build in the valley behind it. On average the pool covers am area of 3.6 sq. km, but during the winter it is drained to cover about 100-1200 sq. meters. The Green Mountain Power Corporation in anticipation of snowmelt performs the annual drainage. In total, the Waterbury Reservoir can hold up to 34, 000,000 cu. Meters of water and services a drainage area of 175 sq. km The Waterbury Dam has been found to cause much disturbance in the stream system in which it is located. This disturbance has been observed in the form of sedimentation up stream of the dam in the reservoir. Changes in the channel below the dam resulting from this sedimentation have also been observed through the use of soil pits and comparative analysis. 1. Location on Aerial Photograph See figure 2 2. Location of Site See figure 1 3. Description of Historic Image:
This image shows a very large dam on the Little River in Waterbury Vermont. To the left of the dam a large reservoir has been created. To the right of the dam roads have been created on the old terraces of the river, and also a house is present. Two men are walking on top of the dam in the foreground of the image. In the background, a wooded hill rises and part of Camel s Hump Mountain is visible. On the far side of the Dam smoke is rising from what appears to be a small settlement possible for workers involved in the construction of the dam. It appears to be summer because the trees are fully vegetated. I would speculate this image was taken shortly after the Dam was completed. This would date this image at about 1939. After the dam was constructed the reservoir filled up with water and sedimentation behind the dam likely began to occur. Flooding episodes would likely still occur above the dam and likely no longer occur beneath the dam. 4. Question What is the disturbance to the stream system caused by the Waterbury Dam? 6. GPS Location of Sites See Figure 1
7. Present Day Image of Site This is the present day image taken from the top of the Waterbury Dam looking east. This image matches the left side of the historical image. The only major difference from the historical image is the sediment deposit that has formed in the far eastern corner of the dam.
This image was taken from the top of the eastern side of the Waterbury Dam looking northeast. In the foreground is a close up of the sediment deposit that now exists in the eastern corner of the Dam. In the background part of Camel s Hump mountain can be seen to place it in context with the historical image.
8. Data Collected Width & Depth 600 563 500 400 Meters 300 200 100 21 40 28.5 30 0.8 1.3 1.3 0 Waterbury River Waterbury Reservoir Little River 1 Little River 2 Width 21 563 28.5 30 Depth 0.8 40 1.3 1.3 Velocity 2.5 2 2.11 Meters per second 1.5 1 1.54 0.5 0.52 0 0 Waterbury River Waterbury Reservoir Little River 1 Little River 2 Velocity 0.52 0 2.11 1.54
Discharge 90 80 78.176 70 Cubic meters per second 60 50 40 30 60.06 20 10 8.736 0 0 Waterbury River Waterbury Reservoir Little River 1 Little River 2 Series1 8.736 0 78.176 60.06 Site Width Depth Velocity Discharge Waterbury River 21 0.8 0.52 8.736 Waterbury Reservoir 563 40 0 0 Little River 1 28.5 1.3 2.11 78.176 Little River 2 30 1.3 1.54 60.06 Waterbury River in Cross-Section 3.5m 0.5 m 21 m 0.8 m 1.2 m 1.1 m 0.75 m 0.4 m
9. Calculations Soils: Waterbury River See figure 3 Little River See figure 4 Manning s n: Because of the high flows below the dam, we were unable to determine the depth of the stream below the dam and therefore unable to determine the value of Manning s n. In order to estimate the value, we obtained approximate depth measurements from USGS Waterbury River Discharge (Q) = 16.8 m 2 x 0.52 m/s Discharge (Q) = 8.7 m 3 /s Manning s n = [16.8 m 2 x (0.74 m) 2/3 x (0.012) 1/2 ] / 8.7 m 3 /s Manning s n = 0.16 Little River Discharge(Q) = 37.05 m 2 x 2.11m/s Discharge (Q) = 78.176 m 3 /s Manning s n = [37.05 m 2 x (0,5 m) 2/3 x (0.018) 1/2 ]/ 8.7 m 3 /s Manning s n = 0.07 10. Conclusions Disturbance to the stream system of the Waterbury River/Little River caused by the Waterbury dam have been observed. The first and primary disturbance is that of sedimentation in the reservoir itself. This can be observed clearly when comparing the historical image to the present day image of the eastern portion above the dam. In the present day image a large deposit exists where in the historical image nothing was present. This is evidence for the trapping of sediments behind the dam that would have naturally traveled downstream. Evidence for this sedimentation can also be observed in figure 5, where a high water mark of sediments in the form of silt are present on the leaves of the annual vegetation. The secondary disturbance caused by the Waterbury Dam can be deduced through examination of the first terrace of the Waterbury River above the Waterbury Reservoir (figure 3), and the first terrace of the Little River below the dam (figure 4). It is assumed that the Dam has not affected the Waterbury River and by comparing the first terrace of the Waterbury River to the Little River one can observe the disturbance the dam has had on the stream system. The Waterbury River s first terrace was dated at about 110 years of age. The Little River terrace was dated at 75 years. These are minimum ages reflecting the age of the vegetation found growing on each terrace. This discrepancy in age is the first clue that
disturbance has taken place in the form of channel change. The age of the Little River terrace also corresponds with the construction of the dam furthering the claim that channel change occurred in the Little River directly related to the construction of the dam. The lack of an A-layer, B-layer, and C-layer in the soils beneath the dam (figure 4) also suggests stream disturbance. Soil horizons form once a terrace is stable. This would suggest that the Little River terrace has been stable for much less time then the Waterbury River Terrace. This could possibly be due to incision of the Little River near the time of construction of the Waterbury Dam. Or simply that the Little River was rerouted at this time leaving a stable terrace 75 years ago. Therefore, no A, B, or C- layers would exist due to the disturbance of the Dam itself. While above the reservoir on the Waterbury River where no dam disturbance has taken place a vast record of sedimentation exists in the cut bank (figure 3). 11. Glaciation Glaciation is a major mode of sedimentation at this field site. Moving from within the stream system away (up-terrace) these episodes of sediment deposition can be observed and the mode of this deposition deduced. Within the stream well-sorted postglacial fluvial alluvium is present. Moving away from the stream system Silt, silty clay, and clay sediments are present. This is found to be reminiscent of a Glaciolacutrine lake bottom formed by retreating glaciers creating ice dams and subsequent lakes. Beyond, a Kame Terrace has been observed where ice contact outwash gravel was found. Finally, Unsorted Glacial Till was observed furthest from the stream system left behind by retreating glaciers at the end of the last Ice Age. 12. Hillslope Activity Hillslope activity was observed in the Waterbury River as well as the Waterbury Reservoir. In both cases this activity served to add sediments to the stream system. Above the reservoir in the Waterbury River slump was seen at the top of the cutbank where the stream itself was causing failure of the hillslope. In the case of the Reservoir, small landslides were observed around the perimeter on steeper sections of the surrounding terrain. These are caused by saturation of the hillslope as the water level changes and failure occurs. 13. Suspended Sediment Observations Through examination of the suspended sediments in samples taken at each site it was found that the Waterbury River above the dam contained the least amount of sediment. The water in the Reservoir itself contained slightly more suspended sediments and the Little River contained the most suspended sediment. We believe that this trend was present because the highest velocity was found in the Little River due to the draining of the reservoir on that specific sample day. We had hypothesized that the opposite trend would be observed. That the most sediment would be found in the Waterbury River, with
slightly less in the Waterbury Reservoir as energy is lost, and sediments settle, and the least amount of suspended sediment in the Little River. Most likely the draining of the dam changed the dynamics of the stream system on this day.
Location Map: Waterbury Resevoir Waterbury River E0679735 N4923116 E 0677234 N4916747 E067723 N4916601 Little River Waterbury Dam = Location of Field Sites Figure 1: This figure shows the location of the field site. The arrows correspond to the location of the specific field sites. Along the Little River, around the Waterbury Dam, and along the Waterbury River north of the resevoir. The scales for the individual maps is included within each map, and the scales are different. GPS points are NAD 83 N
Aerial Photo of the Waterbury Resevoir and Corresponding Field Sites N Little River Site Waterbury Dam Site Waterbury River Site Figure 2: This figure shows the location of the field sites on an aerial photograph of the area surrounding the Waterbury Resevoir.
Waterbury River Just North of Waterbury Resevoir: Terrace 1 O-Layer: Organic layer- 4cm A-Layer: Silt, Sand, gravel- 18cm B-Layer: Red Gravel- 8cm C-Layer: Sand, silt- 38cm B-Layer: Red Gravel- 8cm C-Layer: Fine Silt Parent Material: Cobbles, Sand Silt, unsorted Glacial till W E Figure 3: This figure illustrates a cutbank on the first terrace of the Waterbury River. This image was taken just north of the Waterbury Resevior where the stream has been unaffected by the Waterbury Dam. By the age of the trees this terrace appears to be 110 years old. At least two B-layers are inferred although several more may exist.
Little River Just Below The Waterbury Dam: Terrace 1 O-Layer: Organic Material- 2cm Parent Material: Cobbles, sand, sil, unsorted Glacial Till -This layer continues to stream level W E Figure 4: This figure illustrates the soil pit dug just below the Waterbury Dam on the Little River. The age of this terrace is estimated at 75 years due to the vegitation placing its formation around the time of the Construction of the Dam in 1938. The lack of an A-layer or B-layer is consistent with the young age of the terrace.
Evidence for Deposition E W Figure 5: This image illustrates evidence for deposition just above the Waterbury Dam. The dark line in the middle corresponds to the recent high water mark. The leaves below the line have been covered with sediment. This vegitation is located on the point bar in the western corner of the Dam. = 5cm