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GEOGRAPHY > Hydrology and Fluvial Geomorphology > Flashcards

Hydrology and Fluvial Geomorphology Flashcards

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1
Q

inputs of a drainage basin

A

precipitation in the form of hail dew snow and rain

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2
Q

outputs of a drainage basin

A

evaporation
evapotranspiration
river discharge

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3
Q

stores of a drainage basin

A 
interception 
surface water/depression stores 
soil moisture storage 
groundwater stores 
channel stores
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4
Q

Flows of a drainage basin - above ground

A

throughfall
stemflow
overland flow

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5
Q

Flows of a drainage basin - below ground

A

infiltration
percolation
through flow
base flow

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6
Q

what is evaporation

A

water turns into water vapour through the application of heat

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7
Q

what is transpiration

A

the loss of water vapour from the stomata of the leaves of plants and trees

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8
Q

what is river discharge

A

the volume of water being discharged in a river

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9
Q

what is interception

A

the precipitation that is intercepted before it reaches the ground

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10
Q

what is surface water

A

what stored on the ground surface due to the soil being saturated

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11
Q

what are soil moisture stores

A

water stored between the gaps in the soil

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12
Q

what are groundwater stores

A

water that has percolated into bedrock and is stored in the gaps and cracks of the rock

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13
Q

channel stores

A

the volume of water stored in the river channel

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14
Q

throughfall

A

precipitation that makes it directly to the land surface without being intercepted or dripped of the leaves of plants

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15
Q

stemflow

A

the flow of water from the precipitation down the stems and leaves

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16
Q

overland flow

A

when water runs off the surface of the ground

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17
Q

infiltration

A

when water enters the small opening and pores in the ground from the surface

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18
Q

percolation

A

when water flows down through the soil and underlying rock pulled down by gravity

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19
Q

throughflow

A

the lateral sideways movement of water that has infiltrated into the soil through percolines in the soil

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20
Q

baseflow

A

water that has already percolated into the bedrock below that then moves laterally under gravity to feed springs or rivers

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21
Q

water tables

A

the upper surface of the zone of saturation where the pores and fractures of the ground are saturated with water

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22
Q

phreatic zone

A

the zone that is permanently saturated

23
Q

aeration zone

A

are that is seasonally wetted above the phreatic zone

24
Q

what does an annual hydrograph show

A

how river discharge is affected by rainfall events over the year

25
Q

features of a storm hydrograph (5)

A

peak rainfall - when the highest amount of rainfall

peak discharge - when the river discharge is at its highest

lag time- the time difference between the peak discharge and the peak rainfall

rising limb - when discharge is rising

falling limb - when discharge is decreasing

26
Q

how does climate affect the storm hydrograph (4)

A

type of precipitation - rain that is more liquid means more throughflow

precipitation intensity- harder rain means more run of so shorter lag time and higher peak discharge

temperature - hotter areas means more evaporation so slower lag time and lower peak discharge

antecedent moisture- when soil is retained there is more run off

27
Q

how drainage basin characteristics affect the storm hydrograph (7)

A

size - larger the size the larger peak discharge as it can have more water

shape - long drainage basins have shorter lag times

drainage density - high drainage density means a higher a more rapid response ( short time lag and sharp rising limb)

the porosity of soil and rock - more soluble more infiltration so a longer lag time

slopes - steeper gradient more run of and shorter time lag

vegetation - more vegetation means more evapotranspiration and less infiltration so a lower peak discharge

Urbanisation - through abstraction deforestation and impermeable surfaces

28
Q

erosion (5)

A

hydraulic action- when weight and force of the river flow enters cracks and joints in the bed leading to erosion

cavitation - when air bubbles implode and create small cavities in the rock of the channel bed and sides

solution/corrosion -when acids in the river dissolve the rock on the bed and bank

attrition- rocks rub against each other due to the motion of the water andcreate smoother smaller pebbles

abrasion - coarse and angular rock are dragged along the bed and banks when the scrape and remove fragments from the bed eroding it

29
Q

transportation of load

A

traction - when large load roll along the river bed

saltation - when smaller pebbles bounce along the river bed

suspension - when light sediment float / suspend above river bed by the flow of the river

solution - the transportation of dissolved sediment in solution

30
Q

why does deposition occur

A

the speed of the river decreases
the depth of the water decrease
the river meets still water
the gradient of the channel decreases

31
Q

factors affecting river velocity (4)

A

the gradient of the channel - the steeper the gradient the faster

the volume of water in the channel

the shape of the river channel - the wider and deeper the channel the less friction experienced so the faster the flow of the river

the roughness of the channel - the rougher the channel the more friction so the slower the velocity

32
Q

how to calculate river discharge

A

cross sectional area x velocity of the river

33
Q

patterns of flow (3)

A

laminar flow - found in a smooth straight channel where the water flows the sheets parallel to the river bed

Turbulent: water closest to bed/banks slowed by friction and is overtaken by thalweg. Turbulence created, and water close to banks eddies towards the banks, water close to the bed eddies towards the bed.

Helicoidal: horizontal turbulence produces a corkscrew motion. The thalweg moves both laterally from bank to bank, but also vertically from surface to bed during one rotation.

34
Q

what the thalweg

A

the line of maximum depth and speed of water found along river channel

35
Q

channel types (3)

A

Straight: found when river has low energy, a small amount of discharge and a gentle gradient

Braided: channel is divided by islands or bars. usually when there is a lot of bedload and easily erodable banks, high variable discharged and steep channel

Meandering: channel slope, discharge, helicoidal flow and load combine to a situation where lateral erosion causes the deflection of the thalweg leading to a meander. NOT a result of obstacles.

36
Q

formation of a river cliff

A

when the thalweg laterally erodes the the outer bend of the channel which causes undercutting of the bank creating a cliff

37
Q

formation of point bars

A

they form at the inner bend of a channel where the water floes slower meaning the deposition occurs the is then increase friction and encourages further deposition which builds up over time to form point bars.

38
Q

how pools and riffles form

A

riffle - an accumulation of a river channels sediment caused by the deposition of gravel on the bed of a river channel causing more turbulent flow of water

pools - a deeper area where erosion occurs within a river channel where the river flows in a calmer smoother laminar flow

39
Q

formation a waterfall and gorges

A

river spills over gradient change where more resistant rock is on top of less resistant rock, and splashback undercuts rocks by processes of abrasion. Also produced by rejuvenation, where there is a knick point. Plunge pool removes support for overhang, so collapses. Causes upstream migration.

Gorges: a deep, steep sided valley caused by waterfall retreat.

40
Q

formation of rapids

A

They are formed when the water goes from one hard rock that resists the water’s erosion to a softer rock that is easier eroded. The debris formed by the erosion breaks up the flow of the river, but are not big enough to form a waterfall. Over time, rapids are formed.

41
Q

floodplains

A

flat land made up of alluvium next to the river, rise during floods, as fine silt is deposited.

42
Q

formation of bluffs

A

On the outside of the curve, river currents erode or wear away, the lower part of a riverbank. No longer supported, the upper part of the bank breaks off, leaving the high wall of a bluff

43
Q

formation of levees

A

following a flood event where banks burst, wetted perimeter increases. Increased friction reduces velocity, and coarse material is deposited first around the banks, with finer material moving across the flood plain causing back swamps.

44
Q

deltas

A

sediment is deposited where the river meets a standing body of water, due to a loss of energy. the river cchannel then splits into smaller divergent channels on a delta called distributaries

45
Q

why does deposition happen when a river meets the sea

A

flocculation - the process which causes the salts in the sea to join with the fine clays in the river discharge, the clay particles therefore combine and create larger heavier particles which then fall to the sea bed

46
Q

human impact in the modification of catchment flows - deforestation and afforestation

A

deforestation - reduces interception of rainwater and increases the possibility of surface run off and also increase soil erosion, so a short time lag and the eroded soil will fill the river meaning that the channel capacity will decrease

afforestation does the opposite

47
Q

human impact in the modification of catchment flows - urbanisation

A

creation of impermeable surfaces reduces infiltration and increases overland flow. Sewage systems and storm drains get water to the main channel much quicker than throughflow. Lag times are reduced, and flood peaks are increased. Building on floodplains reduces the available flood space, so flood waters will rise higher.

48
Q

human impact in the modification of catchment flows - water abstraction, grazing and reduction in industrial activity

A

over abstraction causes the drying up of rivers and falling water tables .

Reductions in industrial activity: old springs re-emerge - surface water flooding, basements flood, leakage into tunnels, reduced slope stability.

Grazing: ploughing increases infiltration, heavy machinery causes soil compaction, so reduced infiltration, therefore higher peak discharge. Less evapotranspiration than forested area.Water logging/salination occur with poor drainage.

49
Q

causes of floods - physical (5)

A

Heavy, persistent rainfall (deep weather depressions)

Rapidly melting snow or ice

Impermeable soil and bedrock

Coastal storm surges

Lack of vegetation

Disaster (natural, or dam failure)

50
Q

causes of floods - human (4)

A

Urbanisation (impermeable surfaces, storm drains, channel restrictions from bridges)

Floodplain developments increase risk

Engineering that obstructs the channel

Mechanised farming and poor/inappropriate farming practices.

51
Q

impacts of flooding - human

A 
death
economic losses 
damage ecosystems
affect water quality
increases water borne diseases
52
Q

prediction of floods (3)

A

analysing flood recurrence level - how often, on average a flood of a certain size is likely to occur.

catchment modelling - making of scale models or river basins it helps predict the effect on flood risk of future land use change and climate change, and possible future flood management policies

  • forecasting using satellite imagery so monitor rainfall nd ocean activity to forecast when flood causing events will happen
53
Q

prevention and amelioration of floods - Hard engineering (4)

A

dams - as they can control the amount of water in the drainage basin

channel straightening - the water moves away faster

artificial levees/ floodwalls / embankments - this increases channel capacity

diversion spill ways - take excess water away from the main channel

54
Q

prevention and amelioration of floods - soft engineering (4)

A

afforestation / reforestation - increases interception and stablises the soil

changing farming practices - strip crops( cultivating a field partitioned into long, narrow strips which are alternated in a crop rotation system) to prevent soil erosion

planning - preventing building on floodplains

floodplain retreat - buying of floodplains by he government and allowing them to flood during flood events

GEOGRAPHY (6 decks)

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