Low-head Dams: Explained, Purposes, and Inventory

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Low-head Dams:  Explained, Purposes, and Inventory

2.0 PDHs available

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.

Agenda

Learning objective

Become motivated to participate in creating a National Inventory of Low-head dams.

Target audience

Dam Safety Directors, Staff, and Those in industry who support Public Safety efforts.

Speakers & Bios

Rollin Hotchkiss

Manuela Johnson

Brian Crookston