The Results are in and the Fish Win!
Removal of Two Dams on the Eel River, Indiana
BY DONAVAN HENRY, CARTERVILLE FWCO
With the support from the National Fish Habitat Program and the Ohio River Basin Fish Habitat Partnership, two low-head dams were removed on the Eel River of the Wabash River watershed in north central Indiana in October 2012. This allowed the Eel to flow freely for the first time since the 1840’s. The most downstream dam removed was located near the town of North Manchester and the upstream dam removed was located near the town of Liberty Mills. The removal of these dams resulted in the reconnection of over 190 stream miles. A robust monitoring program of the pre- and post-removal conditions has been ongoing by the project partner, Manchester University, to quantify the physical, chemical, and biological response of the Eel River ecosystem.
Prior to barrier removal, the pool behind the dam at North Manchester extended about one kilometer upstream and the pool at Liberty Mills extended nearly two kilometers upstream. After removal, natural lotic systems began to form upstream with multiple riffle complexes reappearing. Riffles appeared at each previous dam location, and above the North Manchester dam three new riffles appeared at 100, 250, and 500 meters. Likewise, above Liberty Mills two riffles formed at 300 and 500 meters. Excess sediment trapped behind the dams was transported downstream and deposited into the unnatural plunge pools created by the dams. This process was expedited by record flooding in April 2013 (10,400 Cubic Feet/Second (CFS) in a stream that averages less than 100 CFS). Sediment at Liberty Mills filled a side channel with over 5.1 tons of material from upstream of the dam in April 2013, but in March 2014 the channel began to scour and the stream reformed.
With removal of the dams, habitat (QHEI) scores increased more than 20% directly upstream of each dam location and continued to increase further upstream. The increase is a result of riffles and runs being formed upstream by the pool being drained. This habitat is vital to mussels, fish, and other benthic macroinvertebrate species that could not survive in the pre-removal lentic environment. With previously submerged sediment now available for riparian growth and in-stream development, habitat quality and complexity will continue to increase in subsequent years.
The fish community showed a response similar to that of the habitat. Within one year the native fish community above both dams improved from a “Fair/Poor” status to “Good” based on Index of Biotic Integrity (IBI). In the summer of 2013, eastern sand darter (Ammocrypta pellucida) was documented for the first time upstream of the Liberty Mills dam after it was removed. Additionally, the removal of these dams was the first step in opening the Eel River to the Indiana State Endangered Greater Redhorse (Moxostoma valenciennesi). The Eel River is home to the only population of Greater Redhorse in the Ohio River Basin.
The data from this monitoring program illustrated the positive benefits of removing dams from streams, even if the barriers are relatively small. And quantification of these benefits is invaluable for us barrier removal geeks to share with states, municipalities, and civic groups at other potential barrier removal sites.
Removal of the dams was not only ecologically significant; it also increased safety for those who use the river for recreation. In addition, this project provided invaluable research experience for Manchester University students and has raised a tremendous amount of awareness about the Eel River and fish passage, both locally and regionally. This project has helped develop extensive partnerships in the Eel River watershed, resulting in the initiation and/or continuation of many other conservation projects.