cats

how to explain why deposition is the dominant fluvial process in the lower course of a river

while its energy is higher than the other courses???

(it is the second part of a essay topic)

goobeee

here is my opionion
1. gentle gradient
     -->reduce velocity -->lower fluvial energy -->deposition takes place

2. large amount of loads
    -->erosion take place in tributaries -->while they join at lower course -->carried with sufficient large amount of loads -->used up energy -->reduce energy -->deposition take place

3. higher degree of sinousity
    -->due to the  meander becomes mature at lower course-->higher friction generated (i.e. larger wetted perimenter) -->used up energy to overcome friction -->doposition take place

i thk may also can include some human factors
1. higher level of human intervention
   a) Devegetation
   b) farming ( due to available of flat land i.e. floodplain at lower course and alluvium deposit to provide fertile soil)
      ==>vegetation removed -->lack of root + humus -->soil erosion -->more loads washed into river -->deposition and silting

to score higher marks,, different depositional fluvial landforms (as an elaboration to prove there is deposition take place) and examples are necessary.

cats

thank you a lot^^
but why the essay topic state that the energy in the lower course is higher but deposition still take place?

Raelle

energy is the highest at lower course becuase of its greatest velocity

Raelle

hey there, here's my interpretation
energy of lower course is higher than that of upper and middle courses due to its greatest velocity
but deposition still take place is not contradict with its energy
you may think it in this way,
deposition take place when energy of riverwater cannot support to carry the load any more
energy of upper course is less than that of middle course is less than lower course
energy needed for lower course to carry all the load is more than the actual energy of the lower course
therefore deposition take place
but the energy of lower course is greater than middle course or upper course
because energy of upper < energy of middle < energy of lower < energy needed to carry the load

cats

???
why i think after the explanation is more confused><

goobeee

actually lower course really with highest energy among the three courses
as discharge is highest (the tributaries all joint to mainstream at lower course) -->higher discharge higher velocity, thus lower course with highest gross energy.

But the point is,, the net energy of river courses =Gross energy - energy used to overcome friction

Lower course =experienced long period of weathering and erosion, so it carries large amount of loads -->even the energy is higher than that of upper course, but it used up its energy to overcome the friction (i.e. transportation of loads)-->loss energy -->deposition take place.

Upper course with less amount of energy, however the energy used to overcome friction =low, so erosion is dominate in upper course

cats

thank you very much^^

ekwsn

deposition is dominant because of a few factors
1. flood plains
this reduces gradient and while it is dry seasons depositional features like oxbow lakes develop
2. lakes/ sea
when the river enters a large body of water its energy decreases

tikheidennis

River energy concept has nothing to do with deposition.
River energy is largest because of discharge and velocity of the river.

tikheidennis

To answer the first part of your question, about the dominant fluvial process.

The general approach is (mean whenever it is asking the dominant fluvial process):
1. Gradient / steepness
    - lower course have gentle slope
2. Discharge / volume of flow
    - more discharge, as a lot of tributaries join together and water collected from a bigger water catchment
3. Roughness of river bed
    - flat river bed, leading to sheet flow
4. Amount of Load
    - collect a lot of load, to deposit the load accruing to their size
5. River Landform
    - presence of lake and meanders, encouraging disposition