Design, Construction, and Monitoring Practices for Aquatic Organism Passage (2025)
Chapter: Glossary
Glossary
Anadromous fish: Fish that spend portions of their life cycle in both fresh and salt waters and migrate from the ocean to spawn in fresh waters.
AOP water crossing: A transportation structure that crosses over a waterway that has been designed to provide both a safe transportation corridor and channel water flow conditions targeted at accommodating the passage of fish (and other aquatic species).
Aquatic organism passage (AOP): The ability for fish and other aquatic organisms to move freely between habitats on which they rely for food, growth, reproduction, and other needs.
Baffle: A concrete block or metal plate constructed within a waterway structure that is placed to restrain or alter flow conditions within the structure (sometimes referred to as a weir). Hydraulic performance varies with flow. Typically, baffles are placed in waterway structures to increase flow depths, lower water flow velocities, and otherwise create hydraulic conditions for fish passage.
Bankfull: Water level in a stream corresponding to where water is flowing within the banks just before it spills out into the floodplain. Bankfull discharge is a measure of the rate of flow for that condition. Bankfull depth is a measure of the water depth at bankfull discharge. Bankfull width is the width of flowing water when the water level is at the bankfull depth.
Bridge: A structure of any size that consists of a deck supported by abutments, sometimes with piers, with the road surface integrated into the structure.
Catadromous: Fish that spawn at sea and move to and spend most of their lives in fresh water.
Countersinking: A construction method that places the bottom of a culvert or pipe below the final channel bed elevation. Frequently, a countersunk structure will have channel bed material placed in the structure to meet the final channel bed elevation (this is sometimes referred to as embedment).
Culvert: A buried structure that conveys a waterway under a road. Culverts may be boxes, pipes, open-bottom culverts, or the like, where fill is present between the structure and the roadway. The definition of a culvert for the purposes of this study is not limited to the FHWA/National Bridge Inspection Standards (NBIS) 20-ft span limit.
Fish barrier: Anything that hinders fish from migrating up a waterway. Specific to this study, fish barriers typically include culverts with some combination of outlets that have drops exceeding drops seen in the natural channel, shallow flow conditions interior to a structure, or excessive velocities interior to a structure. Fish barriers can be partial or complete barriers, with a partial barrier only traversable by the strongest swimming fish.
Fishway: An engineered structure targeted at providing passage for fish around a fish barrier. Also known as a fish ladder, these structures may differ from an AOP structure by focusing on hydraulic conditions over natural process simulation.
Headcut: A sudden drop in a channel profile typically caused by erosion of the channel working in an upstream direction. Headcuts are typically a sign of channel instability.
National Bridge Inspection Standards (NBIS): Federally established standards for safety inspections of bridges (defined as any structure with a length over 20 ft measured along the roadway centerline) on public roads throughout the United States. The standards require periodic and thorough inspection of bridges.
Non-anadromous fish: Fish that spend their life cycle in fresh water.
Salmonid: Migratory cold water fish species that spawn in shallow waters and spend most of their adult lives in larger waterbodies, including the ocean.
