Initial modeling shows promise for deterrence of Asian carp at lock and dams
When it comes to preventing the upstream movement of Asian carp in the Mississippi River, there’s no single solution. There are, however, physical structures already constructed that may add one more piece to the puzzle – in fact, there are several of them. The Upper Mississippi River has a total of nine Locks and Dams below the one at Upper St. Anthony Falls, which was recently closed as part of the fight against these highly invasive fish. These systems already impede some movement of fish through the Mississippi River, leading MAISRC researchers to ask: how do we maximize the benefits of these existing systems to block Asian carp without impacting native fish?
Researchers Daniel Zielinski, Clark Dennis, and Peter Sorensen are developing a two-pronged system designed to do just that: deterring carps from moving through lock structures with acoustic deterrents; and altering gate operations to create water velocities that prevent carp from traveling through the gates with minimal impact to native fish passage. To tackle the latter part of this project, researchers first have to better understand how water flows in and around lock and dam structures, as well as definitively learn how well Asian carp can swim.
When this work began in 2013, researchers were unsure about the swimming capabilities of Asian carp. Because of silver carps’ impressive ability to jump out of the water, it was thought they were nearly as strong as salmon – the poster child for powerful swimming ability in North America – but this assumption had not been tested.
This summer, Sorensen traveled to the U.S. Army Corps of Engineers’ (USACE) Research and Development Center in Vicksburg, Mississippi, to meet with Dr. Jan Hoover. Together, they used specialized equipment to study the endurance (how long fish can maintain a constant swim speed) of Asian carp at various speeds and determined that Asian carp are considerably weaker swimmers than salmon (watch a video of their mobile swim tunnel experiment here).
Then Zielinski, a civil engineer by training, used this information to create a fish passage computer model that predicts the swimming patterns of silver and bighead carp. He also gathered engineering drawings and bathymetry data (underwater depth measurements) provided by USACE for Lock and Dam #8 – the southernmost lock and dam structure in Minnesota, where USACE will consider initially implementing research findings. Lock and Dam #8 is also home to an experimental acoustic deterrent system which was installed by MAISRC researchers (and funded by the Environment and Natural Resources Trust Fund as well as with the support of private donations) in the lock chamber in 2014.
Partnering with the University of Minnesota Supercomputing Institute, Zielinski used this structural information to create a 3D computational fluid dynamics (CFD) model that includes over 10 million elements and provides velocity and turbulence characteristics for water flowing around and through the dam structure.
Ultimately, Zielinski is running the fish passage model through the CFD model to test a range of fish sizes, speeds, and routes, using the results to identify crucial locations where Asian carp may pass through the gates – and therefore where and when gate operational changes are needed.
This modelling work so far has confirmed that it is possible for water velocities around the lock and dam structures – in some cases created with as little as a 6-inch change in gate height – may exceed the swimming ability of Asian carp.
“By learning how fast and strong carp can swim, along with the velocity at which water is coming out of the dams, we can optimize gate function at the dam to prevent further movement of these fish,” said Zielinski. “Plus, when we combine that with everything we’re learning about the effectiveness of acoustic barriers in the lock, we have a control system that could be very species-specific and highly effective.”
“This is a significant step forward and is certainly better than leaving the door wide open. As long as we can continue making incremental changes that have a positive impact on aquatic invasive species control and potentially the passage of native fish, we’re moving in the right direction,” Zielinski added.
This month, researchers are presenting their initial findings to the USACE, who will review and decide whether any of the recommendations may be implemented at Lock and Dam #8. Going forward with their research, Zielinski and Sorensen hope to more finely tune the models for Lock and Dam #8 and then begin adapting them for use at Lock and Dams #2-7. Stay tuned for further updates as this work progresses!