GEO Chapter 14

River

The trunk stream or an entire river system

Stream

General term not related to size; interchangeable with river. A mixture of water and solids

Functions of a River

Drainage of precipitation in the landscape

Erosion (dislodging, dissolving, or removal of material)

Transportation (the movement of material)

Deposition (when materials are laid down by water) (alluvium)

Base level

The lowest point a stream reaches during its flow, below which it cannot recede. 

Ultimate base level

The ocean

Local base level

A temporary base level limiting the erosion of local streams

Processes to create fluvial landforms

Erosive action of flowing water

Deposition of alluvial material

Drainage basin

An area of land where runoff collects and moves through the same area. Separated by ridges that divide precipitation into different basins

Watershed

A word used specifically to refer to the catchment area of a drainage basin

Internal drainage

Never reaches the ocean or other river systems

Drainage patterns

The ways drainage flows in a particular landscape

Dendritic drainage pattern

Tree-like. Indicates typical landscape conditions and mature drainage developed

Trellis drainage pattern

Major rivers running parallel to each other. Indicates presence of anticlines and synclinal valleys

Radial drainage pattern

Forms at the top of a high peak. Consists of rivers running down from a high point, forming a “radial” look

Parallel drainage pattern

Long tree-like streams that run parallel to each other. Occurs where there is a slope and unconsolidated materials such that the water ends up easily eroding the materials and shedding off of the slopes effectively.

Rectangular drainage pattern

Consists of near 90 degree turns. Occurs when bedrock is present at the surface, and the river follows the bedrock’s joints/fractures.

Annual drainage pattern

Circular, somewhat similar to the radial pattern, but much more circular or “clock-like".” Occurs where a dome is present.

Deranged drainage pattern

Consists of a series of ponds, marshes, and bogs that are poorly connected. Occurs in a newer landscape where the drainage pattern has had less time to develop

Discharge

A stream’s rate of flow. Equal to width X depth X velocity

Velocity

Determines a stream’s rate of erosion or deposition. Represents the energy a stream’s flow has. 

Competency

The ability of a stream to move particles of a given size

Capacity

The amount of material a stream can move

Solution

A stream’s movement of materials via the dissolved load derived from chemical weathering of materials

Suspended load

A stream’s movement of material via fine grained materials held aloft in water

Bed load

A stream’s movement of material via coarse material dragged along the streambed

Fluvial transport

The movement of material through streams

Aggradation

The deposition of sediments in a stream. Associated with slower velocities (decreasing capacity and competency)

Degradation

The removal of sediments and rock from a stream. Associated with faster velocities (increasing capacity and competency)

Types of stream channels

Straight

Braided (several interconnecting channels)

Meandering (single winding channel)

Undercut bank

A degradation feature on the outside of a river bend

Point bar

An aggradation feature on the inside of a river bend

Oxbow Lake

A horseshoe shaped lake that forms when a wide meander from the main stem of a river is cut off from the main stream

Meander scar

Spots where water from a meandering river used to flow but no longer does

Yazoo tributary

A stream running through the backwater area of a large meandering stream

Head

The origin point of a river, where the elevation is highest

Steeper gradient

The steep, rapid decline in water immediately from the head of the river

Longitudinal stream profile

The gradual “midpoint” decrease in elevation in a river

Gentler gradient

The slower decline in stream elevation that occurs near the mouth of a river

Mouth

The lowest point of a river, where a stream ends

Nickpoint

Points in a river where resistant strata cause rapids or waterfalls

Alluvial Terrace

A step-like, relatively level landform of sediment that was once an active floodplain but is now elevated above the current river

Delta

A usually triangular landform, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water

Flood

When high water levels overflow the natural banks and levees of a river. Rated statistically by their probability of reoccurrence based on past experience (questionable accuracy due to limited observation time)

Methods to measure stream flow rates

Staff gauge (depth), stilling well (volume), suspended current meter (velocity)

Urban flooding

The tendency for urban areas to experience increasing numbers of small scale floods because of decreased water absorption of urban building materials