Rivers & Fluvial Landforms

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Freshet

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seasonal big flows in streamsFraser Valley experiences them in late springCorresponds with snow pack levels, precipitation levels, temperaturesFlooding during the freshet accompanies rapid melting of extensive snow pack and heavy precipitation

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How do people determine flood risks in a given year?

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Real-time flow monitoring along the entire streamMeteorological analysis of snow pack and weather patterns

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Floodplain

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The area of flat land near a stream that experiences flooding on a regular basis

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What are floodplains composed of?

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deep layers of sediment

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What are soils deposited by occasional flooding called?

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Alluvial soils - they are rich and fertile

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Why are major cities often located near rivers?

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Corridors of transportation inland from the seaProvide alluvial soils which are rich and fertile for agriculture

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Stream

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A channel in which water flows downhill by the force of gravity

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Drainage basin

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A geographic region drained by a single trunk stream and the smaller tributaries that flow into it.

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Trunk stream

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A single large stream into which smaller tributaries merge

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Tributary

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A stream that joins with other streams to form a larger stream

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Drainage divide

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A ridge or highland that separates drainage basins and defines their boundaries

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Continental divide

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A ridge or highland that separates drainage systems that empty into different ocean basins

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Internal drainage

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A drainage pattern in which streams terminate in a low-lying basin on land

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Fluvial Erosion

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Erosion by running water

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Headward Erosion

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The process by which a stream channel migrates upslope by forming new rills through fluvial erosion

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Stream discharge

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The volume of water flowing past a fixed point within a stream channel; expressed in cubic meters or cubic feet per second

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Factors of fluvial erosion

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Sun - provides heat energy to evaporate water and lift it into the atmosphere Gravity - water that condenses falls as precipitation and gravitational field cut downward into the Earth's surface, transporting rock fragments downslope toward the ocean

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Downcutting

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Water cutting down into the Earth's surface

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Sheet wash

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rainwater that flows downslope in thin sheets

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Rills

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Newly forming stream channels

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Gullies

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Rills that develop in depth

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Interfluve

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The flat areas between stream channels where sheet wash occurs

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Stream discharge Factors

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1. Climate: wet regions = greater discharge 2. Stream order: first order = low discharge 3. Season: Timing of precipitation and snowmelt 4. Surface permeability: greater permeability = low discharge

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Erosion depends on:

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Discharge, flow velocity and channel gradient

Sediment characteristics

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Continuity equation (discharge)

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Q = A*v Q is discharge, A is channel area, v is flow velocity

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What is the effect of heavy precipitation in urban areas as opposed to rural areas?

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Urban areas lands are less permeable, so water flows faster but dissipates quicker than in rural areas

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Abrasion

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The process by which movement of one material wears away another material

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Stream load

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The material that moves within a stream channel

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3 kinds of stream load

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Dissolved load

Suspended load

Bed load

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Dissolved

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load soluble minerals that are carried in solution by a stream

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Suspended load

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Small particles such as clay and silt that remain suspended in flowing water or wind

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Bed load

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Material in a stream channel such as sand, gravel, and rocks that is too heavy to become suspended in the current

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Saltation

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A bouncing or hopping motion of sediment in moving water (or air).

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Traction

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The dragging and tumbling of large rocks in a stream channel

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Hydraulic action

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Frees rock fragments and sets them in motion

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Stream sorting

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Through abrasion and chemical weathering, rocks in a streamed are slowly broken down in smaller and smaller fragments. Sediments are then deposited as a function of size and deposited on a floodplain

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Alluvium

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Sediments deposited on a floodplain by a stream

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Aggradation

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The buildup of sediments in a stream bed

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Braided Stream

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A stream that forms intertwining channels around sediments in the stream bed

Found in steeply sloping areas such as glacial and mountainous environments

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Alluvial fan

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A gently sloping accumulation of sediment deposited at the base of a mountain by an ephemeral stream in arid regions

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Meander

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A looping bend in a stream channel on a floodplain

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Cut bank

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The outside edge of a meander, where erosion exceeds deposition

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Point bar

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An accumulation of silt, sand, and gravel that forms at the inside edge of a stream meander, where deposition exceeds erosion

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Oxbow lake

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A water-filled abandoned channel that results when a meander is cut off from the stream channel

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Thalweg

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The fastest area of flow in a meander

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Meander scar

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A dry oxbow lake region

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Meander neck

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formed from a deepening meander.

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Flood

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Inundation by water in a region not normally covered by water, which results when stream discharge exceeds stream channel capacity

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Flash flood

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A flood that occurs with sudden, intense rainfall or dam collapse, often with little or no warning