The University of Georgia’s River Basin Center has completed a thorough report on what the lower 7 km of the Chattooga River could look like under Lake Tugalo.
By analyzing gradient and slope, cross-sectional width and depth, bed and bank materials and forms, and map view, the UGA team was able to form an impression of what this lower stretch of the river looked like. They gathered this data through historical data (photographs, maps, and survey data), analogs based on digital elevation models (DEM) and the study of the shape of the lower Chattooga River from the U.S. Highway 76 bridge to Lake Tugalo, and hydraulic geometry models estimating channel dimensions.
Pictured above: Map showing the location of the study area. Grey areas are built-up, yellow areas are farmlands, and green is forest. Map tiles by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL.
The River Basin Center team states that stream gradient is the single most important morphological variable of any stream or river channel. This determines the flow velocities and sediment transport capacities that then form the shape of the overall channel. With a combination of pre-dam and modern data, it’s determined that there is a relatively low-gradient channel under the lower 5 km of the lake, but there is a very steep gradient beneath the upper 2 km of Lake Tugalo. There is a sharp change in the river slope at the bottom of the beginning 2 km stretch that marks a significant transition from the steep upper reach to the gentle lower reach of the inundated channel.
The channel width of the Chattooga River between Sections Ill and IV actually goes against standard hydraulic geometry relationships. Instead of widening in the downstream direction, the average river channel width decreases slightly in the downstream direction. However, the bedrock gorge begins a slow widening in the downstream direction at the start of the inundated reach beneath Lake Tugalo. Below that, the river channel widths continue to fluctuate widely through the middle section of the lake.
Pictured above: “Curvature” Transformation of the 1 m horizontal resolution LiDAR DEM showing the large amount of variability in channel width around Woodall Shoals (widest spot) in the Chattooga River. White indicates the greatest amount of concavity of the channel bank. Various bankfull width measurements are shown in meters (m), along with other features (rocks, vegetated bar, parking area).
The best modern comparison to the uppermost 2 km of the river beneath Lake Tugalo is actually the Five Falls of Section IV itself. This 2 km reach really would have been an extension of the Five Falls with a very comparable average slope. Due to the steep gradient, this stretch would have included very steep class IV-V ledges and falls. This portion of the river could have been a stretch of world-class whitewater cascades with great similarities to the Five Falls.
The lower 5 km stretch is much gentler and could have been a great wadable fly-fishing river. It’s also important to note that this stretch has a mixture of materials comprising the riverbed, so there could have been widely varied habitats. This lower stretch is comparable to the Tuckaseegee River between its confluence with Savannah Creek and Dillsboro, North Carolina next to the water treatment plant due to its similar-sized watershed, similar gradient, and fluctuations in materials of the channel beds.
Pictured above: Ground view of the Tuckaseegee River at the water treatment plant just upstream of Dillsboro, NC, looking downstream (photographed by David S. Leigh on 27 October 2022). This is a good analog of what the lowest 5 km of the Chattooga River probably looked like prior to 1923.
We strongly encourage you to read the full report! The River Basin Team with the University of Georgia did a fantastic job explaining each detail. You can find it below.