test 1 - drainage basins

Question 1

What is a drainage basin

Answer 1

a user defined point including all hillslopes and channels draining to that point.

Question 2

What other words are used synonymously for drainage basin

Answer 2

catchment, basin, watershed

Question 3

What is a drainage divide

Answer 3

A topographic control on which way water flows

Question 4

How does a channel initiate

Answer 4

water must move downslope by infiltration or the 4 other types of flow

Question 5

What affects infiltration

Answer 5

soil texture & structure, vegetation, permeability of soil/rock type

Question 6

How does vegetation affect infiltration

Answer 6

limits the precipitation that is able to infiltrate the surface

Question 7

What are the 4 different varieties of FLOW when water reaches the ground surface

Answer 7

Hortonian
Saturation overland flow
Throughflow
Ground water flow

Question 8

What is hortonian flow

Answer 8

Water flowing over a surface, does not infiltrate. Think cities/urban areas

Question 9

What is saturation overland flow

Answer 9

flow that infiltrates below the surface but ultimately returns to the surface

Question 10

What is throughflow

Answer 10

above the water table, moves in a matrix flow or pipe/cavity flow

Question 11

What is ground water flow

Answer 11

Flow that infiltrates through soil profile all the way in to the water table

Question 12

What does groundwater flow sustain

Answer 12

basic flow/water level in a stream

Question 13

How does a channel develop

Answer 13

when the erosive force of overland flow exceeds the resistance of the surface being eroded

Question 14

What are the stages of overland flow

Answer 14

rainbeat impacts
threadflow
sheetflow
rill-flow

Question 15

Explain the stages of overland flow

Answer 15

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

Question 16

How does a channel grow

Answer 16

upwards/headward

Question 17

What is sapping

Answer 17

subsurface flow that can erode overlying sediment which eventually caves in, creating a channel.

just like pipe/cavity flow but associated at greater depths

Question 18

Geologic feature of a channel created by sapping

Answer 18

ampitheatre headwall

Question 19

What are the basic steps of channel network growth

Answer 19

initiation of channel
elongation through headward growth
elaboration/branching as tributaries are added

Question 20

Out of shale or sandstone, which has less infiltration/greater runoff

Answer 20

shale.

Question 21

If water is flowing over a rock, why might it have greater runoff

Answer 21

its surface permeability is very low and/or is is a highly resistant rock

Question 22

Where is stream discharge/velocity the greatest and lowest in the channel

Answer 22

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

Question 23

Does stream velocity increase upstream or downstream

Answer 23

downstream

Question 24

What influences stream velocity

Answer 24

frictional resistance and relief; think huge boulders in the river or water coming in contact with channel edges

Question 25

What is sediment yield

Answer 25

amount of sediment LEAVING the basin. not the same as net erosion rate

Question 26

Why is sediment yield not = to erosion rate

Answer 26

because of sediment storage. on hillslopes(colluvial), and in channels(alluvial)

Question 27

What are the controls on sediment yield

Answer 27

Climate
Vegetation
Basin size
Elevation and relief
Rocky type and its erosional resistance
Land use - increases unless completely urbanized

Question 28

What environment has the greatest sediment yield

Answer 28

Arid / semi-arid regions