River Landscapes Flashcards
What is the confluence?
Where tributary joins larger river
What is discharge?
quantity of water that passes a point on stream or rover bank within giving time period
What is Alluvium?
a sediment deposited by a river when it floods.
What is a floodplain?
flat area forming the valley floor either side of a river channel that’s sometimes flooded.
What is a gorge?
narrow steep sided valley often formed as waterfall retreats upstream.
What is a hydrograph?
graph which shows discharge of a river related to rainfall over a period of time.
What is lateral erosion?
erosion of river banks rather than bed which helps form the floodplain.
What is a levee?
Raised bank found either side of a river formed naturally by regular flooding or built up by people to protect area from flooding.
What is a plunge pool?
deep and turbulent area of water where river plunges over waterfall
What are pools and riffles?
alternating sequence in course of a river that carry coarse sediment where shallow fast flowing sections called riffles are slower sections called pools.
What is vertical erosion?
downward erosion of the river bed leading to waterfall formation
What is thalweg?
course of the fastest flow within a river
What is a tributary?
small stream that joins a larger river.
What is an estuary?
tidal mouth of river where it meets sea-wide banks of deposited mud exposed at low tide.
What is load?
material transported by river
what is mudflat?
areas of fine sediment deposits which over time develop in saltmarshes
What is velocity?
Rate of river flow
What is fluvial erosion?
when a river wears away the land and the ability to erode depends on its velocity
What is fluvial transport?
when river carries load which differs in size such as boulders from upper course and fine slit from lower course
what is the long cross profile of upper course?
Vertical Erosion by hydraulic action
Mostly transported via traction
Large boulders deposited
Very narrow and shallow-V shaped valley
What is the long cross profile of the middle course?
Less vertical erosion and more lateral like abrasion and attrition
Mostly suspended and increased traction load becomes smaller
More deposition especially meanders
Wider and small flood plain.
What is the long cross profile for the lower course?
Very little erosion only lateral like suspension and solution
Small particles of load transported
Fine material deposited
Channel becomes wider and deeper large expanse of floodplain either side of river.
What are features found in upper course?
Interlocking spurs
Waterfalls
Gorges
What are features in middle course?
Meanders
Ox-bow Lakes
What features are found in the lower course?
Levees
Estuarine mudflats
What is the formation of interlocking spurs?
Valley landforms formed by fluvial erosion.
Found in upper course of river where river cuts down into valley.
Areas of hard rock harder to erode river bends around it creating interlocking spurs that link like a zip.
Formation of a waterfall:
Rocks laid down horizontally waterfall will in between hard rock and soft rock downstream. Different rates of erosion means soft rock erodes vertically. Hydraulic action weakens rock behind fall. Undercutting causes overhang unsupported rock falls which caught in water forming plunge pool undercutting continues new overhang process retreats upstream leaving narrow steep sided valley a gorge.
Formation of Meanders and oxbow lake
River erodes laterally causing a bend called a meander. Water undercuts river on outside bend where flow has most energy due to do decreased friction forming river cliff. Inside bend where river is slower material deposited and more friction creating slip off slope. Overtime becomes tighter and continual erosion narrows neck. During flood river has straight path and leaves meander and fastest current flows in centre of river. Deposition occurs beside new deposition seals off ends and cut-off becomes ox bow lake which evantually dies up.
Formation of a Levee
Natural river raised bank found on either or both sides of river channel prone to flooding.
River bursts its bank friction reduces velocity causing deposition. Size of sed becomes smaller across from river.
With each flood banks built up and overtime bed of river develops layer of sediment which raises river channel.
Formation of Estuarine mudflats:
Mudflats form in sheltered where tide is slow. River transports alluvium down sea incoming tide transports sand and slit up estuary.
Where waters meet velocity reduced causing deposition.
Builds layers called mudflats which are covered at high tide and exposed at low.
Mudflats has many creeks and overtime becomes overcome by vegetation.
What is soil water ?
Water held between soil particles
What is Percolation?
Movement of water down through soil
What is Groundwater?
Water stored in rock
What is Transpiration?
water lost through pores in vegetation
What is evaporation?
Water lost from Ground
What is surface run off?
water flowing on top of ground.
What is Throughflow?
water flowing through top soil layer
What is water table
current upper level of saturated soil
What is interception
water absorbed by trees or grass
What is surface storage?
water held on ground surface eg puddles or lakes
What is infiltration?
water skins into soil from ground surface.
What are physical reasons for floods?
Prolonged rainfall
Relief
Geology rocks
What are human factors for floods?
Deforestation
Agriculture
What is peak rainfall?
highest amount of rainfall in period of time
What is Rising Limb?
shows how quickly the discharge rises after a storm
What is Lag time?
Time diff between peak rainfall and peak discharge.
What is falling limb?
reduced discharge once main effect runoff has passed
What is Base flow
normal flow of river when water level is sustained by groundwater flow
What are ways to manage flood risks?
Dams
Planting Trees
Flood plain Zoning
Flood relief channel
Embankments
Channel Straightening
How does flood relief channel reduce risk of flood?
artificial channel is backup channel for river and works as a bypass.
How does flood plain zoning reduce risk of erosion?
land in a river valley used to minimise flooding
