Channels

The 1927 flood that occurred in Vermont brought historic record flows to many streams and rivers throughout the state. Although some events have topped it, such as Hurricane Irene in 2011. However, during that event, rain was centralized in Southern Vermont, and major drainage systems in the Northern part of the state were not affected as bad compared to the flood of 1927. This event scattered the region with 4-9 inches of precipitation across the state. Specifically within the Winooski drainage basin, 4-7 inches of rain occurred causing mass destruction and many fatalities. The USGS gauged the flow around 113,000 cubic feet per second at the peak discharge. (N.W.S.)

Aerial photographs of the Winooski river near Waterbury, Vermont

Figure 1a. above shows a section of the Winooski river southeast of Waterbury directly after the flood in 1927. You can see along the banks and in the adjacent fields/floodplain streaks of white and gray material. This is sediment from the event that was deposited and fell out of load when the flows were receding. One can also notice the missing bridge in the aerial photo. (Figure 1a.) Presumably taken out by floodwaters, due to evidence of water level in the aerial photo and the fact that over 1,000 bridges were destroyed in the major flood event. There is also extensive erosion that can be seen along the far side of the channel on the left-hand part of the 1927 photo. The train tracks look to be destroyed from the erosion of the bank. Looking at the 2004 rephotograph, you can see the increase in human activity near the river. This includes the interstate highway, mining of sediment, a junk yard, and a new bridge can be seen in the center right of the photo. (Figure 1b.) Indication of deposition has occurred since 1927, if you look in the left side of the 2004 picture near the highly eroded cut bank, you can see a mid-channel bar from the result of sediment coming out of load due to a disturbance in flow. More riparian vegetation can be observed in this photo despite the impact from humans. Much of the previous fields from 1927 are now forest. The final figure is from 2020, there is a noticeable difference in the amount of wooded regions since the 1927 photo.(Figure 1c.) Much more vegetation has grown, especially on mid-channel bars. Human activity has decreased from 2004, nevertheless, the floodplain is still a major site for agriculture. (See figure 1c.)

Annual maximum flood probability for the Winooski River at Essex.

The variability of the two data sets is around 25 based on the calculated percent standard deviation. (Figure 2b.) The annual average discharge's percent deviation was calculated to be 24, while the annual maximum discharge events was quite higher at 51. This is okay because one data set is accounting for average while the other is looking at maximum peak discharges. There should be variability due to the data used to calculate the percent standard deviation. The annual average flow is calculated by averaging discharge over a season. Looking at peak flows, one can then look at both datasets and understand that both relate to one another and that when a large flood occurs, the annual average will increase. This is a direct relationship. When thinking about the 1927 flood, since it is an outlier, it certainly skewed the average flow values for the year. A good example of this is the 1936 maximum discharge which was marked at 45,300 cubic feet per second. (Figure 2b.) When looking at the average annual flows, we can see that the average discharge is on average, higher than years with smaller flood events. Although these processes may be different scales, maximum flood events increase the average flood events for the year. When looking at maximum flood events compared to annual, the 1927 flood was recored at 113,000 cubic feet per second and the average annual discharge was is not given. (Figure 2b.) However, looking at the standard deviation, one can predict that the 1927 flood was around 25 times larger than the average annual discharge that was recored.