Friday 17th April 2009 =D
Today we did a recap on River Processes:
1) Erosion
2) Transportation
3) Deposition
So basically, the river erodes the rocks or soil and transports it and then deposits it when there is not enough energy left to carry it. (details are in the previous post by DL =D )
So we went over to the concept of Energy!
What affects the energy of the river?
- Discharge, which is the amount of water
- Velocity, which is based on the gradient, the cross-section/channel shape, and friction)
Discharge is easy to understand. If the river has more water flowing, it has more energy =D
Gradient too, if the river is more sloped (say, a waterfall, then it has more energy)This is due to gravity:
Remember this?
Oh the horror...
Now for Channel Shape.
If the channel is narrower, there will be less friction for the water because there is a greater wetted perimeter/ greater amount of water in contact with the perimeter, thus wetting it/ greater- oh i dunno what la...
(wikipedia puts it as 'the greater the wetted perimeter, so there =D )
Also, wetted perimeter = the cross-sectional area that is 'wet' (courtesy of wiki as well xD)
So a river channel like this
will have more friction than one like this
supposedly, but won't the additional water that figure 1 can hold make up for the increase in the wetted perimeter, thus having a canceling effect or something?
ANYWAY, lastly, we have friction =D
This changes with different types of rocks
Next, we split into groups to try and predict how velocity changes from source to mouth.
btw, the source is defined as the tributary that is furthest away from the mouth =D
My group said that it varies because the friction due to greater wetted perimeter cancels out with the greater amount of discharge, so it's mostly dependent on the gradient, which can change randomly =D
The correct answer, anyway, was that velocity increases downstream as the eroded rocks get smaller and rounder, sediment load decreases, so velocity increases downstream =D
KK so that's basically what we did for lesson xD with this final extra question:
Will a group of salmon travelling upstream to, let's say, Bread, affect the velocity of the river?
My answer: No! xD
Here's a diagram why:
oh look, a fish!
Fishie wags his tail...
Fishie moves forward, Pushing the water infront of it infront...
So now we have a swarm of salmon...
AND VIOLA!!! (i'm sure i spelt this wrongly)
THE ARROWS CANCEL EACH OTHER OUT!!!
you can see that there are the same number of front-arrows as back-arrows =D
And this concludes LLJ's FISH THEORY OF CONSTANT VELOCITY
(All pictures courtesy of ME and Macromedia Fireworks xD [seriously, you all should get this])
Current Geo Challenge Score: 1833 (T.T)
Oh well...
Until next time then...
Well-Wishes
LiangJie
MR HEAH GET WELL SOOOOON!!!!!!!!! <3 (hahas yes i just typed that)
posted by 08ip01 at
12:00 AM
6 Comments:
Your Fishie Theory seems interesting but somehow there is error in you reasoning :D My question is: what force will cancel the push force of the first fish??? and what will cancel the force at the back of the last fish?? :)) To me, i think that those fishes dont have much a significant impact on the velocity of the river.
(Vu Ngoc Quang)
Hello! The fish is sooooooo cute!!! But are you sure that the arrows will be able to cancel out? Cause like what Quang raised, there is no force to cancel out the force produced by the first row of fishes. In the diagram, the arrows cancel out because you used the arrows from the last fish to cancel out that of the first, but I doubt if it is possible in reality.
Yo LLJ nice blog post. Although the fish part is kinda fishy and i dont agree like Jingyi and Quang for the same reason haha ain't possible in reality.
Yeah. Like what the people above said, the force only apply to the individual fishes. If there was no resultant force, they won't even have an accelertaion. Besides, using your theory, its saying that if there was only one fish, it would affect the river's velocity but if there was a swarm, then it would. That kind of doesn't make sense. :D
My view echoes that of Quang :) However,
Even if there is a large shoal of fish swimming upstream against the flow, the fishes are built in such a way that it is streamlined, hence deeming any force output negligible. Moreover, fishes that swim in shoals are normally miniature, thus the force generated is small.
It does affect, to a small extent. A large scale velocity change would be somewhat akin to group of muscular hippopotamuses swimming cohesively upstream, but I believe that is highly unlikely.
I think fishies swimming upsteam would affect the velocity of the strem. Even if the fish was completely stationary, it still presents an obstacle to river flow, somewhat akin to how a rock would disrupt the flow of the river. Dumping a large bunch of rocks into a river would certainly impair the velocity of the river, even if it only causes the water to flow around them, wouldn't there still be friction?
But then again, even if fishies did affect the velocity of the river, i suppose it's effect can only be marginal. I, for one, have never heard of any unusual river activity due to a large swarm of salmon swimming upstream during the breeding season.
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