Hydrology and Fluvial Geomorphology Flashcards
inputs of a drainage basin
precipitation in the form of hail dew snow and rain
outputs of a drainage basin
evaporation
evapotranspiration
river discharge
stores of a drainage basin
interception surface water/depression stores soil moisture storage groundwater stores channel stores
Flows of a drainage basin - above ground
throughfall
stemflow
overland flow
Flows of a drainage basin - below ground
infiltration
percolation
through flow
base flow
what is evaporation
water turns into water vapour through the application of heat
what is transpiration
the loss of water vapour from the stomata of the leaves of plants and trees
what is river discharge
the volume of water being discharged in a river
what is interception
the precipitation that is intercepted before it reaches the ground
what is surface water
what stored on the ground surface due to the soil being saturated
what are soil moisture stores
water stored between the gaps in the soil
what are groundwater stores
water that has percolated into bedrock and is stored in the gaps and cracks of the rock
channel stores
the volume of water stored in the river channel
throughfall
precipitation that makes it directly to the land surface without being intercepted or dripped of the leaves of plants
stemflow
the flow of water from the precipitation down the stems and leaves
overland flow
when water runs off the surface of the ground
infiltration
when water enters the small opening and pores in the ground from the surface
percolation
when water flows down through the soil and underlying rock pulled down by gravity
throughflow
the lateral sideways movement of water that has infiltrated into the soil through percolines in the soil
baseflow
water that has already percolated into the bedrock below that then moves laterally under gravity to feed springs or rivers
water tables
the upper surface of the zone of saturation where the pores and fractures of the ground are saturated with water
phreatic zone
the zone that is permanently saturated
aeration zone
are that is seasonally wetted above the phreatic zone
what does an annual hydrograph show
how river discharge is affected by rainfall events over the year
features of a storm hydrograph (5)
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
how does climate affect the storm hydrograph (4)
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
how drainage basin characteristics affect the storm hydrograph (7)
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
erosion (5)
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
transportation of load
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
why does deposition occur
the speed of the river decreases
the depth of the water decrease
the river meets still water
the gradient of the channel decreases
factors affecting river velocity (4)
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
how to calculate river discharge
cross sectional area x velocity of the river
patterns of flow (3)
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.
what the thalweg
the line of maximum depth and speed of water found along river channel
channel types (3)
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.
formation of a river cliff
when the thalweg laterally erodes the the outer bend of the channel which causes undercutting of the bank creating a cliff
formation of point bars
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.
how pools and riffles form
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
formation a waterfall and gorges
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.
formation of rapids
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.
floodplains
flat land made up of alluvium next to the river, rise during floods, as fine silt is deposited.
formation of bluffs
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
formation of levees
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.
deltas
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
why does deposition happen when a river meets the sea
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
human impact in the modification of catchment flows - deforestation and afforestation
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
human impact in the modification of catchment flows - urbanisation
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.
human impact in the modification of catchment flows - water abstraction, grazing and reduction in industrial activity
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.
causes of floods - physical (5)
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)
causes of floods - human (4)
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.
impacts of flooding - human
death economic losses damage ecosystems affect water quality increases water borne diseases
prediction of floods (3)
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
prevention and amelioration of floods - Hard engineering (4)
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
prevention and amelioration of floods - soft engineering (4)
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
