Fluvial geomorphology Flashcards
(126 cards)
1
Q
who invented stream order system
A
Strahler
2
Q
who invented stream magnitude system
A
Shreve
3
Q
4 sources of streamflow in a small catchment
A
channel precipitation, overland flow, groundwater leading to baseflow, interflow/throughflow
4
Q
what is the max rate for water entry into the soil called
A
infiltration capacity
5
Q
3 factors influencing infiltration capacity
A
vegetation, soil, slope
6
Q
which soil types allow the least and most infiltration
A
sand= most, silt- medium, clay= least
7
Q
is there more infiltration in grasslands or forests
A
forests
8
Q
which type of overland flow is most common in deserts
A
infiltration excess overland flow
9
Q
what is the coefficient of runoff
A
ratio indicating the percentage of rainfall thats converted into overland flow (how much flows awat when all other factors considered)
10
Q
what is the dominant method of water flow to rivers
A
throughflow
11
Q
what type of pores can lead to bogbursts
A
matrix flow
12
Q
name a process that can create macropores
A
bioturbation
13
Q
what pores allow for rapid preferential water or chemical transport
A
macropores
14
Q
in what climates is pipeflow common
A
arid and semi-arid areas
15
Q
give Darcy’s law and what the letters stand for
A
q=KIA q- discharge per unit time K= saturated hydraulic conductivity I= hydraulic gradient A= area being tested
16
Q
what does Darcy’s Law calculate
A
the amount of water flowing through a porous substance
17
Q
what graph is used to calculate the amount of water in a river
A
hydrograph
18
Q
what are the values on the axes of a hydrograph
A
time and precipitation
19
Q
what is the stage of a river
A
its height
20
Q
what do people mean when they say a 1 in 100 year flood>
A
1% chance of a flood in every year
21
Q
why might rain gauges not measure accurately
A
other types of precipitation, local differences in rainfall
22
Q
what device is used to measure river flow
A
river flow gauge
23
Q
3 main methods of river discharge measurement
A
velocity-area method, acoustic gauging, dilution gauging
24
Q
how do you determine the efficiency of the catchment
A
compare amount of water that entered the catchment as precipitation with the amount that came out
25
name 8 factors that affect evapotranspiration rates
solar radiation, air temp., evaporation surface temp, wind speed, humidity, turbulence, plant biology, water availability
26
how can potential evapotranspiration be measured
lysimeter-> block of soil isolated from surroundings and water balance measured
27
give 2 methods for measuring evaporation
atmometers- give direct readings of evaporation, evaporation pan- shows fall in water level
28
what technique is used to measure soil water content
gravimetric- particles weighed, heated and reweighed dry
29
when is the water table not flat
after heavy rain, lies in hollows at surface
30
what percentage of earths non-frozen freshwater supplies are groundwater?
97%
31
what is stemflow
flow of water down plants allowing water to reach the hillslope
32
what is interception storage
storage of precipitation on leaves and tree trunks
33
5 factors affecting surface entry of water
vegetation cover, soil texture, porosity, structure, compaction
34
does well-developed humus and leaf litter layers increase or decrease infiltration capacity
increase
35
what type of flow occurs in the different pore sizes
laminar in matrix pores, turbulent in macropores and pipes
36
which sized pore flow is determined by Darcys Law
matrix flow
37
when does lateral throughflow occur in the matrix
when hydraulic conductivity declines with depth
38
which pores are filled first when water enters soil
small pores, due to greater soil water tension
39
difference between aquitards and aquifers
aquifers- layers of rock porous enough to store water and permeable enough to allow water to flow through, aquitards - aquifers confined between impermeable rock layers
40
what is the baseflow on storm hydrographs derived from
groundwater sources- the "slowflow" element
41
what controls the amount of baseflow
seasonal variations of precipitation, evapotranspiration and vegetation
42
displacement flow
soil water rapidly pushed out by new water entering at the slope bottom
43
flow duration curves
hourly or daily flows grouped in discharge classes where the percentage of time that any particular flow is equalled or exceeded is plotted
44
what does a steep flow duration curve mean
highly variable flows with a large stormflow component
45
what does a gentle flow duration curve mean
large baseflow component
46
what is a river regime
a seasonal variation in river flow that tends to be repeated annually
47
how is a river regime often expressed
monthly discharge
48
3 things that can control the river regime
climate of region, catchment geology, soils
49
when is discharge greatest in glacial regions
early summer due to melt
50
fluvial flooding
river overflows its banks
51
pluvial flooding
heavy rainfall leads to concentrated overland flow inundating an area
52
groundwater flooding
concentrated zones of saturation-excess overland flow
53
coastal flooding
tidal surges, storm surges and tsunamis
54
4 major river regimes
1. dominated by snow and ice melt
2. temperate oceanic areas
3. tropical
4. equatorial
55
snow and ice melt river regime
major peak in late spring/early summer
56
temperate oceanic areas river regime
precip all year, autumn/winter maximum, evapotranspiration peak in summer
57
tropica river regime
high precip in summer, dry season in winter, all year high evapotranspiration
58
equatorial river regime
bimodal distribution of precipitation
59
flashy regimes
steep mountainous areas: intense precipitation episodes and large flood peaks
60
subdued regimes
lowland catchments with permeable rock: smaller flood peaks
61
how does sediment usually enter a river
in pulses, often seasonal
62
where does most river sediment come from
headwater in the mountaisn
63
what conditions lead to the most sediment in rivers
250-350mm precip and sparse vegetation
64
what major factor can alter sediment yield in rivers
humans- ploughing, deforestation, construction
65
typical sediment in tropical
silt and clays
66
typical sediment in temperate
silts and clays, some sands and gravels in mountains
67
typical sediment in arctic and alpine
coarse and silt sized
68
5 degrees of freedom in channel morphology
slope, channel width, depth, channel planform, bed roughness
69
describe Horton's stream order
source stream = first-order stream, two first-order channels meet to generate a second-order stream
70
what was Strahler's adaptation to Horton's stream order
main channel remains a first-order stream along its length
71
main stream lenght
distance of main river channel from source to length
72
total stream length
combined length of all components of the channel network
73
drainage density
drainage area divided by the total stream length
74
bank-full conditions
when discharge just fills the channel (flow resistance at a min)
75
what is the hydraulic radius of a river cross section
the area divided by the wetted perimeter
76
3 broad types of channel planform
straight, meandering, braided
77
what is channel sinuosity
ratio of the length of river between two points to the length of the valley between these two points
78
what is the sinuosity of straight channels
less than 1.5
79
what is channel multiplicity
total length of perimeters of sand and gravel bars divided by length of channel reach
80
how can channel multiplicity change
as water levels rise and fall
81
what is the imbrication of particles at a river bank
long axes of particles aligned along the flow direction
82
2 principal forces governing velocity of water flow and amount of flow in a channel
gravity and friction
83
what does the Manning equation measure
the mean water velocity in an open water channel
84
isovels
lines of continuous velocity
85
where are velocities usually greatest in a river
mid channel, close to stream bed
86
thalweg
area of maximum velocity in a river- moves from the inner to the outer bend
87
can can cause erosion in a river despite shear stress being quite low
turbulence and eddies
88
hydraulic sorting
finer particles moved downstream more easily
89
stream competence
largest size of particle a stream can carry as bed load
90
stream capacity
max volume of sediment a stream can carry
91
dominant discharge
the flood discharge that achieves the greatest total geormorphic work
92
dynamic equilibrium in river channels
channel form oscillates around an average
93
relaxation time
time taken for a channel to return to original form after a flood event
94
what factors usually change downstream
cross sectional area increases, boundary roughness decreases, velocity increases
95
3 processes forming potholes in bedrock channels
corrasion, corrosion and cavitation
96
autogenic river channel change
fluctuations in channel form about an equilibrium condition
97
allogenic river channel change
adjustments of channel form in response to a change through time in the sediment and water regime of a river
98
avulsion
process where channel shifts from old to new course, leaving intervening area of floodplain intact
99
effects of wetland removal
runoff conducted downstream faster in greater volumes, flashier regime
100
impact of river engineering (removing meanders)
flashier regime and more likely to flood
101
what is the wetted perimeter
the part of the perimeter in touch with the river
102
main type of flow in fluvial systems
turbulent
103
what does Reynolds number determine
if the flow is laminar or turbulent
104
what is a flow and riffle
pool: streaming flow
riffle: shooting flow
105
what is subcritical flow
tranquil, streaming flow, Froude number less than 1
106
what is supercritical flow
rapid or shooting flow, froude number over 1
107
hydraulic jump
sudden change from supercritical to subcritical flow
108
what does the Hjulstrom diagram show
the relationship between flow velocity and particle size (what velocity will cause entrainment)
109
3 transport methods for load
suspension, saltation and traction
110
effect of suspended load on the river flow
reduces the inner turbulence and makes it look muddy
111
why may water with high suspended load not mix easily with normal water
it is denser
112
3 main channel types
bedrock channels, alluvial channels, bedrock/alluvium mixed channels
113
7 storage locations for sediment in the drainage basin
slope storage, alluvial fan, colluvium, floodplain deposits, channel deposits, delta, lake bed
114
3 zones in a catchment
zone 1: production, zone 2: transfer, zone 3: deposition
115
4 factors controlling the reworking of sediment stores
type of store, volume and calibre of sediment, vegetation cover, distance from the channel
116
2 types of floodplains
lateral and vertical accretion floodplains
117
helicoidal flow
circular pattern flow that moves sediment around the bend
118
lateral accretion floodplain
meandering rivers, banks build outwards, scars of old meanders left behind,
119
vertical accretion floodplain
fine material that settles out of suspension during overbank flows, graded bedding, levees (coarser sediment dropped first)
120
features of a non-cohesive meandering floodplain
point bars, lateral accretion
121
features of a low-energy cohesive floodplain
natural levees, vertical accretion, back swamp, crevasse splay where natural levees are breached
122
paired terrace
matched with terrace across the valley
123
unpaired terrace
migrating river removes evidence of the opposite terrace
124
characteristics of braided rivers
abundant bedload, erodible bamks, high stream power, variable discharge
125
characteristics of meandering rivers
lower stream power, smaller sediment size, lower gradient
126
3 types of meandering rivers
fine-grained, low-sinuosity fine-grained, anastomising fine0grained
