Rivers Flashcards
national levees
these are raised banks of sedinment parallel to a river channel formed by deposition of coarser sediment during floods §
draingage basin
also known as watershed is the highest land bordering the basin. rivers are the main features of a drainage basin
processes- drainage basin
interception- precipitation falling into the drainage basin can be intercepted by leaves and ground vegetation
infiltration- some of the precipitation that reaches the ground continues downward through soil
overland flow- some of the precipitation reaching the ground flows over the surface until it reaches a river channel
evaporation- water on vegetation or in river channel get evaporated back into the atmosphere
through flow- infiltrating water continues down slopes through the soil towards the river channel
groundwater flow - some infiltrating water continues into pores and cracks in the underlying rock and cracks in the underlying rock and flows towards the river as groundwater.
river processes
source- upper
–> highland- middle
—> lowland- lower
—> mouth
transportation
rivers carry eroded material :boulders, pebbles, sand, silt. this is caller a river’s load this can be don in several processes:
- traction
- saltation
- suspension
- solution
traction
rolling large particles along the riverbed
saltation
bouncing of smaller particles along the riverbed
suspension
carrying fine particles in the water collumn
solution
dissolving soluble materials
alluvial plains
these are flat areas of land adjacent to rivers, fomred by the deposition of sediment carried by the river overtime.
deltas
form at the mouth of a river where it meets a body of water, such as a sea or lake. sediment carried by the river is deposited, creating a fan-shaped landforms with multiple distributions
meanders
are bends or curves in a river’s course, formed through the lateral erosion of the riverbanks and the deposition of sediment on the inside of bends
hydraulic action
force of the water knocks particles off the sides
corrasion
wearing down of rock by the river’s load(abrasion)
attrition
waering down of big rocks by colliding together and breaking in the river
solution/corrosion
acids in the river dissolve the rocks that make up the bed + banks
erosion and speed
as the speed of the river increases, so does the amount of erosion and load in a river
river deltas
formed at the mouth of a river where sediment is deposited, creating a network of distributariesfl
floodplanes
are flat area of land adjacent to rivers, periodically inundated to the formation and replenishment of floodplains
river course
goes through three stages : upper, middle, lower
length of these depends on type of rock, landscape, climate
refers to its journey from source to mouth
upper course
river has a V-shaped valley with a steep gradient, water in river channel occupies most of the valley floor
load is large bc not enough time to erode
load found at bottom
lots of friction between water and bed-load = decease velocity
common features: waterfalls, rapids, potholes
waterfalls
occur where the river crosses resistent rock and the softer rock downstream is eroded more rapidly
under waterfall is plunge pool is formed when erosion by hydraulic action and abrasion is greatest.
potholes
if riverbed is uneven, pebbles become trapped and swirl currents cause pebbles to rotate and erode circular holes in riverbeds
alternating hard and soft rock forms uneven bends and areas of rapids
features of the middle course
river cchannel is wide and deeper w/ gentler valley sides and a wide flood plain
river ahs joined by its tributaries at points of confluence
lateral erosion - more important than verticle erosion so, meanders are formed
bedload size decreases, more chance of depostion
main features- meanders, oxbow lakes and waterfalls
meanders
more erosion on side where velocity is greatest
on fast-flowing side, river cuts into bank and becomes deeper
increasing deposition forms slip-off slope
oxbow lakes
as meander get bigger outsides bend closer together
in times of flood, river might erode to find a straight way and cut of meanders neck
old channel becomes an oxbow lake, may dry out and vegetation will grow in its place
features of the lower course
river is broad and deep
bedload transported in suspension/solution and deposition
fast-flowing = very little friction
common landforms- floodplains, alluviun, levees and mouth
flood plains
area either side of channel which floods if river bursts in its banks
covered in clay, salt and sand from flooding (alluviun)
levees
river’s edge have natural ridges
mouth of a river
estuary- wide deep end of river
narrow mouth
delta- mark the end of river’s long profile
Mississippi river in USA
biggest river in USA
source 446m at lake itasca, Minnesota
has a waterfall (falls of st.anthony)
many tributaries add to river
—> increasing load
different type of rocks means 60m gorges and meanders
influenced development in US
silt, deposits make for fertile land
sugarcane, rice, tabacco, cotton
transport route
500mil tonnes of stuff transported along river
92% of US’s agriculture comes from there
recreational opportunities
tourism (11mil each year)
sport, fishing, waterfowl
29 power plants
flooding
types of river management
hard engineering
soft engineering
hard engineering
is when artificial structures are constructed to change the shape of the river channel or manage the way that a river flows.
soft engineering
is when engineers work with nature to try to reduce the likelihood of river flooding
what do soft engineering strategies allow
Soft engineering strategies allow a river to flow more naturally. The river is managed so that:
it slows down
is able to store water and release it slowly.
soft engineering strategies
planting trees in the upper catchment to soak up water
blocking up old field drains so that rainwater takes longer to get into the river
felling trees across small tributaries so that the flow of water down these streams is slowed down
replacing artificial straight sections of river with more natural meandering sections.
what do hard engineering strategies allow
Hard engineering strategies are used to artificially manage rivers to reduce the risk of erosion or flooding.
hard engineering strategies
dredging the river to make it deeper. This increases the capacity of the river.
widening or straightening the river so that it flows more quickly
building embankments or walls to prevent water spilling over the top of the bank.
