Chap 10

How does stream discharge do its erosive work? What are the processes at work on the channel?

'STREAM CHANNEL PROCESSES - the geomorphic work performed by a stream includes EROSION and DEPOSITION, which depends on the volume of water and the total

What is a river delta? Give some examples.

Extensive lower plain covered by an intricate maze of distributaries formed in an ARCUATE (arc-shaped) pattern. Ex: Ganges and Brahmaputra Rivers in South Asia

Describe the formation of a floodplain. How are natural levees, oxbow lakes, backswamps, and yazoo tributaries produced?

FLOODPLAIN: A flat, low-lying area long a stream channel, created by and subject to recurrent flooding: alluvial deposits generally mask underlying rock. NATURAL LEVEES: A long, low ridge that forms on both sides of a stream in a developed floodplain: a depositional product (coarse gravels and sand) of river flooding. OXBOW LAKES: A lake that was formerly part of the channel of a meandering stream; isolated when a stream eroded its outer bank, forming a cutoff through the neck of the looping meander (SEE Meandering stream). RIPARIAN MARSHES: YAZOO STREAM: A small tributary stream draining alongside a floodplain: blocked from joining the main river by its natural levees and elevated stream channel. "...YAZOO STREAM, also known as YAZOO TRIBUTARIES, which fllow parallel to the main river but are blocked from joining it by the presence of natural

Stream gradient

The angle, measured in the direction of flow, between the water surface (for large streams) or the channel flow (for small streams) and the horizontal. Also known as stream slope.

Oxbow Lake

The crescent-shaped body of water located alongside a stream in an abandoned oxbow after a neck cutoff is formed and the ends of the original bends are silted up. Also known as crescentic lake; cutoff lake; horseshoe lake; loop lake; moat; mortlake

Suspended load

The part of the stream load that is carried for a long time in suspension. Also known as suspension load.

Nickpoint

The smallest unit in a composition, depending on the scale of the work; it may be composed of straight lines and arcs, forms (flowing and curvilinear), or a combination.

What role is played by rivers in the hydrologic cycle?

The water in the hydrologic cycle is stored in any of the following reservoirs: the atmosphere, oceans, lakes, rivers, soils, glaciers, snowfields, and under the Earth's surface as groundwater.

Saltation

Transport of a sediment in which the particles are moved forward in a series of short intermittent bounces from a bottom surface.

Traction

Transport of sedimentary particles along and parallel to a bottom surface of a stream channel by rolling, sliding, dragging, pushing, or saltation.

Floodplains

an area of low-lying ground adjacent to a river, formed mainly of river sediments and subject to flooding

Alluvial terrace

composed of alluvium rather than carved in solid rock, resulting from a change in the regimen of the stream from alluviation to downcutting

Bed load

describes particles in a flowing fluid (usually water) that are transported along the bed.

Dissolved Load

especially ions from chemical weathering, that are carried in solution by a stream.

Delta

is a landform that forms at the mouth of a river, where the river flows into an ocean, sea, estuary, lake, or reservoir.

Alluvium

is loose, unconsolidated (not cemented together into a solid rock) soil or sediments, which has been eroded, reshaped by water in some form, and redeposited in a non-marine setting.

Deposition

is the process where materials like mud, sand, pebbles and silt are transported by the river and are eventually dropped.

Flood

occurs when a river bursts its banks and the water spills onto the floodplain.

Braided stream

river is one of a number of channel types and has a channel that consists of a network of small channels separated by small and often temporary islands called braid bars or, in British usage, aits or eyots.

Yazoo tributary

stream that runs parallel to, and within the floodplain of a larger river for considerable distance, before eventually joining it.

Competence

the ability to do something successfully or efficiently

Aggradation

the deposition of material by a river, stream, or current

Capacity

the maximum amount that something can contain

Abrasion

the process of scraping or wearing away

Degradation

the wearing down of rock by disintegration

Discharge

volume of water which flows through it in a given time.

Hydraulic Action

when the motion of water against a rock surface produces mechanical weathering.

Describe the flow characteristics of a meandering stream. What is the pattern of the flow in the channel? What are the erosional and depositional features and the typical landforms created?

1) A gradual channel slope 2) Streams with a more sinuous (snakelike) form. 3) Remarkable looping pattern. 4) The outer portion of each meandering curve is subject to the fastest water velocity, it undergoes the greatest erosive, or SCOURING. SCOURING can create a steep UNDERCUT BANK, or CUTBANK. 5) The inner portion of each meander experiences the slowest water velocity and thus is a zone of fill (or aggradation) that results in a POINT BAR, an accumulation of sediment on the inside of a meander bend. 6) Laterial erosion creating MEANDER SCARS. 7) Actively meandering streams erode their outside banks as they migrate, often forming a narrow neck of land that eventually erodes through and forms a CUTOFF. 8) Oxbow Lakes, creating when meanders become isolated from the rest of the river. 9) Thalweg = zone of maximum depth.

What is the sequence of events that takes place as a stream dislodges material? Differentiate between stream competence and stream capacity.

1. EROSION: water dislodges, dissolves, or removes weathered surface material. 2. Material transported to new locations. 3. DEPOSITION: Materials are deposited into a new location.

Graded Stream

A stream in which, over a period of years, slope is adjusted to yield the velocity required for transportation of the load supplied from the drainage basin

Meandering Stream

A stream that has multiple successive meanders and develops in relatively flat areas, such as a floodplain, where sediment consists primarily of fine sands, silts, and muds.

How does a stream transport its sediment load? What processes are at work?

A stream transports its sediment load when the force of flowing water is GREATER than resistant forces. Via hydraulic action, the stream erodes, loosens and lifts rocks.

Natural levee

An elongate embankment compounded of sand and silt and deposited along both banks of a river channel during times of flood.Nickpoint