2. Long And Cross Profiles Flashcards
What is a long profile?
Shows the gradient of a river as its journey from source to mouth. The source of a river is where it starts and the mouth is where it reaches the sea
What is the graded long profile?
When a river tries to achieve a smooth curve in order to reach its base level at the sea
How does the upper course of a long profile change? (Erosion, transport, deposition)
Erosion : vertical erosion due to hydraulic action
Transport : traction, large boulders moved
Deposition : large boulders deposited
Why? High relief and trickles merge into single channel with steep gradient and potential energy. Waterfalls, rapids
How does the middle course of a long profile change? (Erosion, transport, deposition)
E :less vertical erosion,more lateral,attrition,abrasion,solution
T: suspension,increased traction, load becomes smaller/less angular
D : more deposition, especially on inside of meanders
Why? Hilly, discharge increase as channel is deeper and vol of water is more by many tributaries. Energy means less vertical erosion and lateral erosion at meanders. As vertical reduces, gradient of lip becomes concave
How does the lower course of a long profile change? (Erosion, transport, deposition)
E: v little erosion, only lateral
T: suspension/solution, small particles and great quantity of load
D: d now main fluvial, fine maturely deposited
Why? Close to mouth, where land is low, erosion confined to lateral at meanders, lack of erosion means gradient is flat
What is discharge and how does it increase downstream? (How it’s measured and equation)
Volume of water passing through a given point on a river
Cubic meters per second (cumecs)
Discharge = velocity x cross sectional area
Increases downstream as tributary streams join main river and add water to their vol
How does velocity increase downstream and what is it?
Increases along its course. Despite steep descent in uc because small channel means low friction, the lc has greatest velocity
Depends on how much water comes into contact with channels banks and bed
What is a cross profile?
section taken sideways across a river channel and/or a valley
Channel cross profile only includes river
Valley cross profile includes channel, valley floor and slope up sides of the valley
How and why does a channel cross profile change downstream?
UC : narrow and shallow MC : becomes wider LC : becomes wider
In uc the river erodes it’s bed by abrasive and hydraulic action, as it travels tributaries join to increase vol of water (giving kinetic energy, higher velocity and erosive power), allows to cut much deeper downstream
As gradient becomes steep, less vertical erosion, by time in middle course erosion is dominant
How does a valley cross profile change downstream?
UC: steep sided, narrow v shaped valley. River channel takes up most of floor
MC: valley broadens out , small flood plain, sides not steep
LC: large expanse of flat flood plain on either side of river
why does a valley cross profile change downstream?
In uc vertical erosion creates slope that weathered material can fall down and then removed once reached the river, but the rock is harder in upland areas so not much weathering (slopes steep)
In mc river meanders and erode laterally into valley sides and broadens out and rate of weathering increases but as energy is used for erosion the material builds up
In lc deposition from floods builds up flood plain and meanders migrate, widens valley
