What Lies Beneath: Density Currents in the Chicago River

Urbana Middle School, Urbana, IL

Bringing his research into the classroom, Mr. Jackson taught the UMS WaterWorks students about the inportance of density in natural water bodies such as rivers, lakes and the ocean. The WaterWorks students used clear plastic tubs and special dyes used at the U of I to create density currents in the classroom. By introducing water of different temperatures and salinities to a clear plastic tub of room temperature freash water, students were able to produce buoyant overflows, intrusions, and density currents all because of small differences in the density between the water in the tub and the dyed water. Students were able to create up to 7 different layers in their tanks! At the end, students were allowed to experiment with waves and mixing.

Following the lab exercise, Mr. Jackson gave a lecture on other density currents in nature and in particular, density currents that form in the Chicago River in the winter. Mr. Jackson showed pictures of how the U of I measures density currents in the field and the lab and he discussed some of the data. He also showed how U of I researchers are using super computers to study density currents. Density currents in the Chicago River are thought to be due to salinity and temperature differences. Salinity differences are believed to be due to salt used on roads for deicing during the winter. Visit Mr. Jackson's website for more information on density currents in the Chicago River.

(Left) Mr. Jackson helps one group prepare for the experiment. (Right) Water was mixed with dye to create a visualization of the current (dyed water in jugs).

(Left) Mr. Jackson explains the procedure for the experiment. (Right) Group 1 pours hot water into the room temperature reservior through a hole in the side of the tank.

(Left) A buoyant overflow created using hot purple water. (Right) A density current created using green cold water.

(Left) The density current can be seen traveling across the bottom of the tank. (Right) WaterWorks students get a better view of their experiments.

(Left) After the currents have ceased, three distinct layer are visible. (Right) As the upper hot water cools (purple), it sinks into the lower layers creating dye streaks.

(Left) The currents created secondary circulations in the small tanks as shown by these vortices. (Right) The final product is a stratified flow with 7 layers.

The groups and their experiments.

(Right) Mr. Jackson relates the density current lab to research at the University of Illinois and density currents on the Chicago River.

Computer simulation of a density current produced at the University of Illinois (image courtesy of Mariano Cantero)