Glossary of River Terminology

A brief introduction to some of the terms used on this web site.

Agricultural Area Supported
geographical area of agricultural activity within the river catchment area

Anabranch
a section of a river or stream that diverts from the main watercourse channel (or mainstem) and rejoins the mainstem downstream.
In the simplest case, an island or rock in the river creates a main course and an anabranch course; a more significant anabranch would diverge for a distance of several kilometres before rejoining.  River deltas branch into large numbers of courses, though these are not normally regarded as anabranches, as the net result is usually multiple discharge points rather than a rejoined unified flow.

Catchment (Drainage) Area
the area draining into a river or tributary

Delta
a deposit of soil, usually triangular, formed at the mouth of some rivers

Earliest Human Settlement
earliest archaeological evidence of human settlement

Human Population Supported.
numbers of humans resident within the catchment area

Industrial Area Supported
geographical area of industrial activity within the river catchment area

Length
distance from source to mouth, following the route of the water

Mainstem
the principal river within a given drainage basin, in the case where a number of tributaries discharge into a larger watercourse. Viewed in terms of the Strahler Stream Order system, the mainstem would be the highest order stream amongst the streams in a given drainage basin. The United States National Weather Service considers the mainstem as the principal object of flood forecasting. In detailed analyses of riverine hydrology, mainstem also refers to precise channel mapping of the principal drainage; for example, in a braided channel or system with anabranch elements the mainstem is designated as the principal braid or channel within the overall river.

Rain Forest Area Supported
geographical area of rain forest within the river catchment area

Source
the point from which a river springs

Strahler Stream Order
The Strahler Stream Order is a simple hydrology algorithm used to define stream size based on a hierarchy of its tributaries. The streams range from one at the headwaters (which is a "1") to the most powerful which is the Amazon River which is a "12." The Ohio River is an "8" and the Mississippi River is a "10." 80 percent of the streams and rivers on the planet are first or second order. 

To qualify as a stream it must be perennial. When two first-order streams come together, they form a second-order stream. When two second-order streams come together, they form a third-order stream. Streams of lower order joining a higher order stream do not change the order of the higher stream. Thus, if a first-order stream joins a second-order stream, it remains a second-order stream. It is not until a second-order stream combines with another second-order stream that it becomes a third-order stream. It is important to appreciate that stream order is dependent upon map scale. As scale decreases and more detail is added to the river network (i.e. new tributaries) then a river may increase its stream order.

Arthur Newell Strahler first proposed the hierarchy in 1952 in an article “Dynamic basis of geomorphology,” in the Geological Society of America Bulletin. It is often referenced in professional descriptions of rivers as Strahler 1952.

Tributary
a stream or river which flows into a mainstem (or parent) river, and which does not flow directly into a sea. In orography, tributaries are ordered from those nearest to the source of the river to those nearest to the mouth of the river. A confluence is where two or more tributaries or rivers flow together.  The descriptive terms right tributary and left tributary always apply from the perspective of looking downstream (in the direction the is going), similarly to the river banks.  The opposite of a tributary is a distributary; a river branch that flows away from the main stream. A river and all its tributaries drain the watershed of the river.

Urban Area Supported
geographical area of urban conurbation within the river catchment area

Last Updated on 04/07/07
By Dr Martin