Ch 11

Graded stream

A condition in a stream of mutual adjustment between the load carried by the stream and the related landscape through which the stream flows, forming a state of dynamic equilibrium among erosion, transported load, deposition, and the stream's capacity.

Delta

A depositional plain formed where a river enters a lake or an ocean; named after the triangular shape of the Greek letter delta, Î".

Alluvial fan

A fan-shaped fluvial landform at the mouth of a canyon; generally occurs in arid landscapes where streams are intermittent.

Alluvium

A general descriptive term for clay, silt, and sand, transported by running water and deposited in sorted or semisorted sediment on a floodplain, delta, or streambed.

Drainage pattern

A geometric arrangement of streams in a region determined by slope, differing rock resistance to weathering and erosion, climatic and hydrologic variability, and structural controls of the landscape.

Hydrograph

A graph of stream discharge over a period of time (minutes, hours, days, years) at a specific place on a stream. The relationship between stream discharge and precipitation input is illustrated on the graph.

Flood

A high water level that overflows the natural (or artificial) banks along any portion of a stream.

Oxbow lake

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 a looping meander (see meandering stream).

Parallel

A line, parallel to the equator, that designates an angle of latitude (see latitude; compare meridian).

Natural levees

A long, low ridge that occurs on either side of a river in a developed floodplain; depositional by-products (coarse gravels and sand) of river-flooding episodes.

Floodplain

A low-lying area near a stream channel, subject to recurrent flooding; alluvial deposits generally mask underlying rock.

Stage gage

A pole marked with water levels.

Undercut bank

A steep bank formed along the outer portion of a meandering stream, produced by lateral, erosive, undercutting action of a stream (compare point bar).

Braided

A stream that becomes a maze of interconnected channels laced with excess sediments. Braiding often occurs with a reduction of discharge that affects a stream's transportation ability or an increase in sediment load.

Competence

A stream's ability to move particles of a specific size and is a function of stream velocity and the energy available to move materials.

Flash flood

A sudden and short-lived torrent of water that exceeds the capacity of a stream channel; associated with desert and semiarid washes.

Traction

A type of sediment transport that drags coarser materials along the bed of a stream (see bed load).

Stream

Also referred to as river.

Fluvial landscapes

Are a result of ongoing erosion, transport and deposition of materials in a downstream direction.

Entrenched meanders

Caused after the river actively returns to downcutting.

Rejuvenated

Caused by a meandering stream flowing through the uplifted landscapes.

Trellis drainage

Characteristic of dulling of folded topography

Bed load

Coarse materials that are dragged along the bed of a stream by traction or by the rolling and bouncing motion of saltation; involves particles too large to remain in suspension (see traction, saltation).

Bajada

Continuous apron.

7 drainage patterns

Deandritic Trellis Radical Parallel Rectangular Capture Annular Deranged

Erosion

Denudation by wind, water, and ice, which dislodges, dissolves, or removes surface material.

Base flow

Describes the low discharge during dry periods.

Drainage density

Determined by dividing the total length of all stream channels in the basin by the area of the basin.

Peak flow

Determined by the amount, location and duration of the rainfall episode.

Radial

Drainage pattern that results when streams flow of a central peak or some such as occurs on a volcanic mountain.

Super imposed

Drainage system may flow in apparent conflict with older, buried structures that have been uncovered by erosion so that the streams appear

Stream piracy

Elbows of capture

Continental divides

Extensive mountain and highland regions separating drainage basins sending flows to the pacific, Gulf of Mexico, the Atlantic, Hudson Bay, or the Arctic Ocean.

Perennial streams

Flow all year, fed by snowmelt, rainfall or ground water, often in some combination.

Intermittent streams

Flow for several weeks or months each year and may have some groundwater inputs.

Ephemeral streams

Flow only after precipitation events and are not connected to groundwater systems.

Rectangular

Formed by a faulted and jointed landscape, which directs stream courses in patterns of right-angle turns.

River system

Formed by a network of tributaries.

Drainage divides

Formed by ridges that define the catchment (water-receiving) area of every drainage basin.

Point bar

Formed by the inner portion of a meander experiences the slowest water velocity and thus receives sediment fill.

Capture

Headward-eroding part of one stream could break through a drainage divide and _______ the headwaters of another streak in the next valley.

Interfluve

High ground that separates one valley from another and directs sheet flow.

Deranged

In areas having disrupted surface patterns with no clear geometry in the drainage and no true stream valley.

Base level

Is a level below which a stream cannot erode its valley

Ultimate base level

Is at sea level, the average level between high and low tides inclined upward under the continents.

Alluvial terraces

Level areas that appear as topographic steps above the stream; created by a stream as it scours with renewed downcutting into its floodplain; composed of unconsolidated alluvium (see alluvium).

Dissolved load

Materials carried in a stream in chemical solution derived from minerals such as limestone and dolomite or from soluble salts.

Annular

Produced by structural domes with concentric patterns of rock strata guiding stream courses.

Longitudinal profile

Side view of a stream.

Rills

Small-scale downhill grooves that mar develop into deeper gullies and then into a stream in the valley.

Stage

Stream depth is measured as the height of the stream surface above a constant reference elevation (a datum).

Exotic stream

Stream of high potential evapotranspiration rates in arid regions may cause dish argue decrease with distance downstream.

Fluvial

Stream-related processes; from the Latin fluvius for "river" or "running water."

Transport

The actual movement of weathered and eroded materials by air, water, and ice.

Drainage basin

The basic spatial geomorphic unit of a river system; distinguished from a neighboring basin by ridges and highlands that form a divide.

Gradient

The drop in elevation from a stream's headwaters to its mouth, ideally forming a concave slope.

Hydraulic action

The erosive work accomplished by the turbulence of water; causes a squeezing and releasing action in joints in bedrock and is capable of prying and lifting rocks.

Suspended load

The fine particles held in suspension in a stream. The finest particles are not deposited until the stream velocity nears zero.

Aggradation

The general building up of land surface because of deposition of material; opposite of degradation. When the sediment load of a stream exceeds the stream's capacity, the stream channel is filled through this process.

Disharge

The measured volume of flow in a river that passes by a given cross section of a stream in a given unit of time; expressed in cubic meters per second or cubic feet per second.

Abrasion

The mechanical wearing and erosion of bedrock accomplished by the rolling and grinding of particles and rocks carried in a stream, moved by wind in a "sandblasting" action, or imbedded in glacial ice.

Nickpoint

The point of interruption of the longitudinal profile of a stream shows an abrupt change in gradient, such as at a waterfall or an area of Rapids.

Deposition

The process whereby weathered, wasted, and transported sediments, deposited by air, water, or ice, are laid down.

Elbows of capture

The sharp bends in two of the streams and is evidence that one stream has breached a drainage divide.

Meandering stream

The sinuous, curving pattern common to graded streams, with the outer portion of each curve subjected to the greatest erosive action and the inner portion receiving sediment deposits (see graded stream).

Capacity

The total possible load that a stream can transport.

Saltation

The transport of sand grains (usually larger than 0.2 mm, or 0.008 in.) by stream or wind, which bounce the grains along the ground in asymmetrical paths.

Sheetflow

The water that moves downslope in a thin film as overland flow, not concentrated in channels larger than rills.

Dendritic drainage

Treelike pattern is similar to that of many natural systems such as capillaries in the human circulatory system or the vein pattern in leaves of tree roots.

River

Trunk, or main stream.

Fluvial erosion

Weathered sediment is picked up for transport to new locations.

Superposed stream

Where an existing stream flows as rock is uplifted, the stream keeps its original course, cutting into the rock in a pattern contrary to its structure.