Apron

Erosion protection replacing or reinforcing stream bed in an area of high velocity flow such as downstream of a culvert.

Baffle

Obstruction, usually wood, concrete, or metal placed inside a culvert to deflect and check the flow of water.

Burst Speed

The highest rate of speed a fish can generate for a short period of time (such as several seconds).

Cruising Speed

The speed at which a fish can swim indefinitely.

Debris

See trash.

Design Discharge

A quantity (rate) of flow that is expected at a certain point as a result of a design storm or a specific low flow condition. Usually expressed as a rate of flow in metres³ per second.

Fish Migration

The movement of individual fish and/or fish populations for any purpose, including feeding, spawning, etc.

Ford

A road crossing a stream where a hard causeway is provided in the bed of the stream.

Fry

Juvenile salmon and trout in their first few months of life.

Gabion

A patented woven or welded wire basket filled with rocks of such a size that they do not pass through the openings in the basket. Individual baskets are stacked in place like building blocks and filled with rock to form erosion resistant structures.

Gradient (slope)

The rate of rise or fall of a slope - expressed as a percentage or ratio as determined by a change in elevation to the length.

Inlet

Entry point to a culvert.

Invert

The lowest internal point of any cross section in a culvert.

Manning's Formula or Equation

An equation for determining the quantity of flow whose factors are the hydraulic radius, cross section area of flow, and a coefficient of roughness, Manning's n.

Outlet

Exit point from a culvert.

Parr

Juvenile salmonids between the fry and smolt stages.

Passage Design Flow Range

The flow range used in assessing fish passage parameters.

Peak Flow

The maximum instantaneous rate of flow during a flood.

Perching

The development of a fall or cascade at a culvert outlet due to the erosion of the stream channel downstream from a culvert barrel, bridge apron or ford.

Pipe Arch

Multi-plate or structural plate culverts assembled on a treated timber or concrete foundation. Because of their size (normally in excess of 2 m in diameter) and the fact they are placed on a foundation, they are normally assembled on site. A series of interlocking steel plates are bolted together to make the required shape and length. Many older pipe arches have been formed using brick.

Return Period

A statistical term defining the probability of occurrence of an (in years) event. Thus a 1-in-50 year return period flood (also referred to as the 50 year flood) is one likely to be equalled or exceeded only once on average in a 50-year period.

Salmonid

Any of the fish belonging to the family Salmonidae such as salmon and trout.

Scour

Term used to describe soil erosion when it occurs underwater as in the case of a stream bottom or bank.

Smolt

The juvenile downstream migrant stage of salmon and sea trout.

Trash

Any buoyant or semi-buoyant material carried by the flow of water in a channel but which could form a blockage in a culvert. Also referred to as debris.

Weir

Small dam in a stream that causes water to back up behind it, and flow over or through it.