Low-Head Dams

Low-head dams, a.k.a. “drowning machines”, are ubiquitous throughout the U.S. and have killed hundreds of people in the past few decades, with the numbers increasing each year. Although their size and upstream conditions do not make these structures look intimidating, dangerous recirculating hydraulics can form at the downstream face that will drown any unsuspecting person who passes over the dam. Due to their small height and lack of water storage, low-head dams and the safety concerns that they present have slipped through the cracks in dam safety management. For this reason, low-head dams are poorly documented. This trend is especially true in California, where even a rough estimate of the number of low-head dams has not yet been possible. This study presents a new inventory method that utilizes category designation and unique attribute tagging to assign hazard potential to low-head dam structures in California. The primary purpose of this study is to introduce the idea of hazard potential ratings for use in low-head dam inventories, and to provide a sample that exemplifies a first step that California can take in mitigating this significant public safety concern. The resulting open-access interactive map can be used to prioritize the most hazardous low-head dams and inform subsequent mitigation options for 226 located structures in 2 specific study sites within California.

To test the inventory methodology, the study area was designed to be a cross-section of California’s diverse landscape, land use, and river use. The rivers with a fatal low-head dam with at least one documented fatality were located. These rivers and their tributaries are Study Area 1. Study Area 2 is the major streams and their tributaries in Sacramento County which provides a complete inventory sample within a well-defined political boundary. Both study areas are combined in the interactive map below.

Download the full paper by Spencer Lacy:

Introducing a California Low-Head Dam Inventory Methodology