Low-head Dams: Explained, Purposes, and Inventory

A low-head dam is a structure that is designed and built such that water passes over the crest continually from bank to bank. These structures, also known as diversion dams and grade control structures, serve to provide a reliable water surface elevation upstream for diversion purposes or to control streambed incision. There are thousands of these structures in the U.S. dating from colonial times to the present. Besides presenting a barrier to upstream aquatic organism passage, conditions on the downstream side of the dam can present serious dangers to recreationists. Hydraulic jumps form on the downstream side of low-head dams, and if the downstream depth is deep enough, the jump becomes submerged and forms a powerful reverse current called a “hydraulic.” In these conditions, anyone passing over these innocuous-looking dams becomes trapped with very little chance of survival. Those involved in attempted rescues also risk their lives. These issues will be illustrated with examples and basic hydraulic theory. Potential actions for those responsible for these structures include installation of signage, dam rehabilitation, or dam removal. Many of these dams are no longer used for their original intent, while others continue to provide essential services. To increase public awareness of the dangers and issues associated with low-head dams, the work of a national Task Force on the Creation of an Inventory of Low-head Dams will be described. Opportunities to assist in this work will be explained to webinar participants. Eligible for 2 PDHs

Rollin Hotchkiss

Professor, Civil and Environmental Engineering

Brigham Young University

Dr. Rollin Hotchkiss is a professor of civil and environmental engineering at Brigham Young University. He is currently chairing a joint Task Force comprising members of USSD, ASDSO, and the Environmental and Water Resources Institute of the American Society of Civil Engineers to create a national inventory of low-head dams. Besides working to reduce fatalities at such structures, Dr. Hotchkiss conducts research in extending the useful life of dams and reservoirs and applications of machine learning in water resources. He is a professionally licensed civil engineer and holds advanced professional registration with the American Academy of Water Resources Engineers.

Manuela Johnson

Administrator of the State Disaster Relief Fund (SDRF), and Indiana Silver Jackets State Lead

Indiana Department of Homeland Security

Manuela Johnson works at the Indiana Department of Homeland Security in the Response and Recovery Division. She is the administrator of the State Disaster Relief Fund. She is the State Lead for the National award winning Indiana Silver Jackets Team. The Indiana Silver Jackets has been actively working to draw public awareness to the issues associated with low head dams. During the last legislative session Indiana passed a law directed specifically at safety at low head dams.

In addition, Manuela serves as co-Vice Chair of the Joint Task Force on Low-head Dams and is a member of the ASDSO Safety AT Dams subcommittee.

Manuela graduated from Indiana Purdue University at Indianapolis (IUPUI) with a Bachelor’s degrees in Chemistry and Biology. Manuela has worked and volunteered in public safety and emergency management for nearly 40 years. She holds a number of firefighting and EMS certifications and has served as a certified fire service instructor and fire investigator. She is married and enjoys gardening, photography, volunteering at her church and working as a safety team member for motorsports events regionally.

Brian Crookston

Assistant Professor, Civil and Environmental Engineering Department, and Utah Water Research Laboratory

Utah State University

Brian Crookston is an Assistant Professor at Utah State University in the Civil and Environmental Engineering Department and at the Utah Water Research Laboratory. His research group is focused on water sustainability and resiliency including: hydraulic structures, fluvial hydraulics, and modeling and technology. Brian has particular interest in public safety at low-head dams along with the hydraulics of spillways, chutes, energy dissipators, nonlinear weirs, physical and numerical modeling, machine learning algorithms, flow acoustics, scour and erosion, ecohydraulics, embankment failures, flooding, and surface hydrology. Brian serves as co-Vice Chair of the joint Task Force on Low-head Dams and as Chair of the USSD Spillways subcommittee. He and his wife have five fantastic kids and love spending time together in a very wide variety of family activities.