Alec Mulkern '22 and Michael Kutsanzira '23

Alec Mulkern '22 and Michael Kutsanzira '23: Research with David Harbor, Summer 2021

This summer, we worked with Dr. David Harbor refining experimental equipment and gathering data to study the mechanisms which cause river bedrock erosion by plucking. Our work was divided into two projects: developing and executing experiments using the scale-model lab flume and working in the field with our custom sensor capsule to study a real river. As engineering majors, our focus was to improve the mechanical design of the lab flume and field sensor capsule, develop data logging and plotting software, and collect data from both the lab and field equipment.

The lab flume consisted of a step to create a hydraulic jump over a model of a cracked riverbed. The riverbed was made of 3D printed plaster blocks with a controlled crack aperture. Dye was injected under the plaster blocks to monitor the upstream fluid flow in the sub-bed; a factor which helps initiate plucking. Seven piezoelectric pressure sensors measure the pressure under each block and send measurements to our data logging software. The field sensor was a capsule which fit into a piece of cracked bedrock in Cowpasture River, VA. This sensor measures and records pressure above and below the rock as well as its inertial data. We hope to correlate the lab data with the field data to illuminate the mechanisms behind plucking.

As with any technical undertaking, constant unexpected setbacks forced us to hone our problem-solving skills and decision-making abilities. One major discovery was that the design and location of the flume made the pressure sensors susceptible to vibration-induced noise from both the floor of the lab and the attached water pump. The noise overpowered any meaningful pressure data from the experiment. Along with changing the location of the flume to a more stable floor, we redesigned the sensor attachments, and added vibration-dampening foam and rubber to key contact points to isolate the pressure sensors.

This summer's experience with Professor Harbor challenged us as engineers and allowed us to communicate across disciplines in search of a common goal.

Supported in part by SRS and the R. Preston Hawkins IV Award