Thursday, April 9, 2009
April 7th entry
Today Mr Faizhal went to our class and told everyone to read the textbook page 240, which is about the River channel processes. Here is a summary of these 2 pages:
Water energy depends on: the amount of water
the steepness of the slope.
Competence: ability of river to transport sediment.
Load: material carried by the river.
Sediment movement depends on:
1) Nature of the bed and banks
2) The flow of the river
3) Human intervention.
Erosion: the picking up and removal of material. Three processes of erosion:
1) Corrasion (most significant type): particles of rock carried by the river grind away at the bank and bed.
2) Hydraulic action: water crashes on onto the bed or against the banks.
3) Solution: Carbon dioxide in water may react with limestone and chalk.
Deposition occurs where particles can not be carried any more due to the small flow speed. Some places where it can occur: inside bend of meander, bed of river, close to river’s bank, where river enters the sea, etc.
Velocity is the main factor controlling transportation, erosion and deposition.
The Hjulstrom curve has a critical erosion velocity line and a critical deposition line. Basically, it is like this:
- The larger the particle the greater the velocity required to pick it up. (It makes sense right)
- However the small particles tend to stick together, so higher velocity required to pick them up. (It also make sense right?)
- Velocity falls, successively smaller particles drops.
There is an increase in velocity with distance downstream, due to:
- Greater volume of water, because water from many sources join the main flow.
- Roughness of channels is reduced because silt replaces pebbles and boulders è less turbulence.
- Channel tends to adopt more efficient profile.
It was raining romantically today, that’s why Mr. Faizhal asked the whole class to go out and look at the rain. We observe the overland flow, the process of interception and the maximum infiltration capacity of the land. We observe the flow of water outside 01 classroom. We discussed the hydrograph of a random point along the flow. The hydrograph should be very steep with a short lag time.
That’s all we have for today lesson. It was quite interesting as the whole back row people were laughing all the times, and no one slept in class.
-Lam-