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Dam Removal on Cathy Jo Branch at the Nashville Zoo
Project Date: February 2017
Location: Nashville, TN
Waterway improved: Cathy Jo Branch
Restoration methods: Dam removal, monitoring
Dam removals at the Nashville Zoo
A map indicating the location of Nashville, TN.

In February 2017, the Compact removed two dams in Cathy Jo Branch, adjacent to the entrance of the Nashville Zoo. Like many other urban streams, Cathy Jo Branch’s water quality has been negatively impacted by habitat alteration, excess sediment, nutrients and pathogens, and low dissolved oxygen. The dams were contributing to almost all these issues, and after removal, many in-stream conditions improved quickly and dramatically. Today, 700-800 feet backwater are flowing again. 

Both dams on Cathy Jo Branch were roughly 4’ high and about 50’ wide. Endangered Nashville Crayfish are found in the watershed, so prior to removal, crayfish sweeps were conducted. Nashville Crayfish and other priority species were relocated prior to deconstruction work.

A group of men and women move standing in and around a stream, wearing waders and carrying buckets.
Prior to removal, the Compact and its partners found and relocated Nashville Crayfish.

Removal of the dam enabled backwaters to flow freely again. Improved connectivity has allowed for easier species migration and increased genetic diversity within the creek (eliminating the “aquarium” effect produced between multiple dams on a single waterway). 

Two men using construction equipment working on a dam.
The construction team at KCI removing one of the two dams on Cathy Jo Branch.

In addition to dam removals, this project included the addition of gravel and slab rock along nearly half a mile of stream to create riffle habitat and boost water quality. Riffles provide essential habitat for numerous species of fish and invertebrates like crayfish. They also aerate water, allowing dissolved oxygen – essential for aquatic plants and animals – back into the formerly oxygen-deprived waterway.

A close up of ripples in a creek.
Riffles returned to Stewart Creek after removal of the Sam Davis dam. Photo by Jed Grubbs

Further work included creating a small wetland in the stream’s floodplain to retain stormwater and reduce sediment and nutrient pollution entering the waterway. Roughly 1.5 acres of existing stormwater detention basins that filter the zoo’s parking lot runoff were enhanced with a mix of native grasses and wildflowers. These native plants have improved the basins by slowing and filtering stormwater, as well as providing wildlife habitat. 

Streamside habitat and stability were enhanced along approximately 1,000 feet of stream, where invasive species were removed and native seed and live stakes were planted. All areas disturbed by construction machinery were stabilized with straw, native seeds, and live stakes. 

What was once a stagnant backwater with a sediment-filled bottom is now a mix of diversified habitat including riffles (fast and turbulent shallow water), runs (fast and smooth deep water), and pools. Flowing water prevents nutrients from pooling and causing harmful algal blooms, and it prevents sediment from building up and burying bottom-dwelling microorganisms beneath the muck behind the dam. Many aquatic species are sensitive to temperature increases, and the water that flows through Cathy Jo branch today stays cooler than the slow-moving water that previously heated up behind the dam under the sun. Three years of subsequent monitoring showed continued stability and improved habitat. 

A woman inspects a healthy creek.
Cathy Jo Branch after the dam removals.

This work was done in partnership with the Nashville Zoo Conservation Staff, US Fish and Wildlife, Maddox Charitable Fund,  KCI Technologies, the US Department of the Interior, TN Wildlife Resources Agency, and the TN Department of Environment and Conservation.