test 1 - drainage basins Flashcards
What is a drainage basin
a user defined point including all hillslopes and channels draining to that point.
What other words are used synonymously for drainage basin
catchment, basin, watershed
What is a drainage divide
A topographic control on which way water flows
How does a channel initiate
water must move downslope by infiltration or the 4 other types of flow
What affects infiltration
soil texture & structure, vegetation, permeability of soil/rock type
How does vegetation affect infiltration
limits the precipitation that is able to infiltrate the surface
What are the 4 different varieties of FLOW when water reaches the ground surface
Hortonian
Saturation overland flow
Throughflow
Ground water flow
What is hortonian flow
Water flowing over a surface, does not infiltrate. Think cities/urban areas
What is saturation overland flow
flow that infiltrates below the surface but ultimately returns to the surface
What is throughflow
above the water table, moves in a matrix flow or pipe/cavity flow
What is ground water flow
Flow that infiltrates through soil profile all the way in to the water table
What does groundwater flow sustain
basic flow/water level in a stream
How does a channel develop
when the erosive force of overland flow exceeds the resistance of the surface being eroded
What are the stages of overland flow
rainbeat impacts
threadflow
sheetflow
rill-flow
Explain the stages of overland flow
rainbeat move sediment through impacts
threadflow is integrated raindrops into thread-like flow
sheetflow is integrated threadflow into laminar flow
rill-flow is sheetflow concentrated into small parallel streamlets
How does a channel grow
upwards/headward
What is sapping
subsurface flow that can erode overlying sediment which eventually caves in, creating a channel.
just like pipe/cavity flow but associated at greater depths
Geologic feature of a channel created by sapping
ampitheatre headwall
What are the basic steps of channel network growth
initiation of channel
elongation through headward growth
elaboration/branching as tributaries are added
Out of shale or sandstone, which has less infiltration/greater runoff
shale.
If water is flowing over a rock, why might it have greater runoff
its surface permeability is very low and/or is is a highly resistant rock
Where is stream discharge/velocity the greatest and lowest in the channel
greatest at the center near the top, lowest at the channel edge/cut bank/bottom; think friction against the water; where is friction lowest = highest velocity
Does stream velocity increase upstream or downstream
downstream
What influences stream velocity
frictional resistance and relief; think huge boulders in the river or water coming in contact with channel edges
What is sediment yield
amount of sediment LEAVING the basin. not the same as net erosion rate
Why is sediment yield not = to erosion rate
because of sediment storage. on hillslopes(colluvial), and in channels(alluvial)
What are the controls on sediment yield
Climate Vegetation Basin size Elevation and relief Rocky type and its erosional resistance Land use - increases unless completely urbanized
What environment has the greatest sediment yield
Arid / semi-arid regions
