Unit 5: Streams Flashcards
What are the 4 types of stream channels? define them
Meandering: A stream that meanders throughout a valley or floodplain creating point bars and cutbanks
Anastomosing: multichannel, with two or more streams interconnected over a large floodplain (quite laterally stable)
Braided: Abundant supply of sediment; rapid and frequent variations in water discharge and form with erodible banks,
Bedrock: Channels that do not scour or erode quickly; stream is consistently confined
What is a Stream? What evidence must it have?
-A watercourse having and alluvial sediment bed when water flows on a perennial or intermittent basis between continual, definable streambanks
-Must have evidence of fluvial processes deposited by moving water
What are the 3 zones of streamflow? Define them
Zone 1: Headwaters - streams flow swiftly through deep, V-shaped mountain slopes; waterfalls and rapids occur here
Zone 2: Transfer zone - lower elevation streams merge to flow down gentle slopes. Streams widen and begin to start meandering
Zone 3: Depositional zone - lowest elevations where streams meander across broad, flat valleys and floodplains
Where does the highest stream velocity occur?
Just below the surface and in the middle of the stream (lowest friction from lack of contact with air and streambanks) / thalweg
Why does a point bar and cutbank form?
A point bar forms where streamflow is the slowest and sediment is deposited. A cutbank forms where streamflow is the fastest and sediment is eroded
What occurs during bankfull? what happens if it continues?
The flow of a channel has filled entirely up to its banks. If water levels continue to rise, they will spill over into the floodplain
What are characteristics of ALLUVIAL STREAMS
-Active fluvial unit: bed and banks are of sediment and actively erode
-The channel can erode and freely transport sediment
-Has Large Woody Debris (LWD) and typically fish habitat
-Riparian vegetation typically limits bank erosion
-Riffle / Pool and cascade / Pool - channel bed
What are characteristics of NON-ALLUVIAL STREAMS
-Not an active fluvial unit: Cannot freely erode and will not readily change its channel dimensions
-Confined by bedrock / riprap / soils / woody materials
-Not sensitive to disturbance
-Transport zones and LWD may trap sediment
-Cascade / pool, step-pool, or rock dominated
Define:
Cascade channel
Step-pool channel
Riffle-pool channel
CC: Found in step mountain zones, large grain sizes (boulders & cobble), typically narrow in width
SPC: channel spanning pools and cobble/boulder steps
RPC: gradient <2%, moves laterally in a predictable way, bar development, alternates between riffles and pools
What are factors that affect channel morphology?
- Bank composition and structure
-Non erodible (basal till, bedrock) limits erodible movement
-Erodible units promote movement - Slope & channel gradient
- Human channel alterations (culverts, riprap, bridges, flood protection works)
- Streamflow
What are indicators of a recently scoured channel?
-eroded banks
-scoured channel bed
-few pools
-debris levees
-buried debris in channel
-structures removed
What is the Riparian Area?
the area adjacent to banks of the stream, lakes, and wetlands
What are some characteristics of the riparian area?
-High soil moisture content
-highly diverse and critical habitats, home ranges and travel corridors for wildlife
-streamside vegetation protects water quality, provides bank stabilization, regulates stream temperatures, and is a continual source of woody debris (nutrient sources and habitats)
