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
