If there is programme to prevent flooding at the middle course. How the features of the channel change?
Ms Leung's response:
Brilliant questioning mind :) Appreciated! Yes, it'll be a heat question in public exam. We'll touch on it in unit 2.5. It'd be lovely if smart students can respond to this brilliant question. Try!
A river source is usually a spring where underground water gets onto the ground surface. Want to know how the source of Chang Jiang was found? Pls watch this video: http://www.youtube.com/watch?v=9u3s6i-V2Qg (for the river source: pls go straight to 2'15")
For a more details of a trip to "follow a river to the source" http://www.youtube.com/watch?v=NH1IghSJwhE (for the river source: pls go straight to 5'10")
Ms Leung's response: There are only uuper and middle courses of rivers in HK. The lower course of rivers usually pass through urban areas / new towns, so they're all channelized , i.e. the river course is straightened. So we can't see mature meanders in HK.
If there are some obstacles on the channel, will this cause waterfall?
Ms Leung's response: Obstales on the channel usually form turbulence. Rapids & potholes, etc are formed. Waterfalls are closely related to outcrops of resistant rocks.
What is the factor lead to the formation of delta?
Ms Leung's response:
There are 2 main factors for depostion: 1. Large amount of loads 2. Small amount of energy (river / sea)
Under what conditions will there be large amount of loads transported to the sea? Under what conditions will there be smaller amount of river energy? --> Who'd like to answer these 2 challenging questions?
During revision, I ve read Ch 2.3. But I what I dont understand is that the lower course has the largest discharge overall = largest river energy, right? However, the lower course favours deposition landforms. Also, the upper course shall have the least river energy, but the major fluvial process is erosion. Isnt that the larger the river energy, the more erosion occurs?? Why is there such phenomenon?
Ms Leung's response;
You have an inquiring mind. Appreciated :)
You have correct concept on the general relationship between river energy and fluvial processes. Clever girl !
I think you can pay attention to the following prinicples in studying relationship / correlation between X and Y.
1. If X is the cause and Y is the result,
you should note if X is the only cause.
--> Cause & effect are not linear usually.
--> There are often multiple causes and even mulitple effect.
For example, one of your queiry is, "If there is little energy in the upper course, why isn't there a lot of deposition?"
The conditions for deposition: (1) Yes, little energy. (2) Supply of sediments.
In the upper course, river water has just started running (starting from the source). There is not enough time and energy for erosion. So there is little supply of sediments. How can there be deposition? 無遮無扇,神仙都難變啦~
2. How can we define the major / dominating fluvial process? It is defined in terms of proportion, not in absolute amount.
For example, just for comparison (the following data are NOT true value):
Amount_______Upper course______Lower course
Discharge__________10______________1000
Erosion_____________7______________200
Transportation______2______________100
Deposition__________1______________700
(Assuming: 1. the units are the same; 2. The amount of fluvial processes equals to the amount of discharge.)
In terms of absolute amount, the lower course has the largest discharge, so all the fluvial processes are large in amount.
But in terms of proportion, in the upper course, the proportion of erosion is the largest. In the lower course, the proportion of deposition is the largest.
Q.4 If there is programme to prevent flooding at the middle course. How the features of the channel change?
Response by Chong Sum Ping:
The feature of the channel become straightened river banks become symmetric and river bed becomes smoother.
The speed of water flood increase natural erosion and the position decrease transportation increase.
Advantage of flood prevention Reducing the risk of flood along the middle and lower courses of the river is able to prevent the “once-a-century”(百年一遇) flood.
Disadvantage of flood prevention Increase the risk in flooding in upper course threatens the safety in the lower courses regions is the dam collapses.
Soil erosion in the upper course will increase the sediment in the river. Thus, the transportation mainly takes place. When the river flows to a reservoir, where water is kept beyond the dam. As the river discharge is low, so deposition is the major process. Therefore, the sediment deposits on the river bed and thus silting takes place. This will raise the river level (river bed) and hence reduce the river capacity. Flooding will be more likely to happen.
Q11 Sometimes, the waterfall is not so high or straight, like the waterfall in 新娘潭, so how can we classify rapids and waterfall?
Response by Chong Sum Ping:
Rapids is a section of fast-flowing, turbulent running water Develop when there is hard rock dipping downstream. The soft rock downstream is worn away more quickly, leaving the hard rock sticking up into the river channel. Waterfall is a vertical fall of water in the water caused by abrupt change of the channel slope over a short distance
Question 1:
回覆刪除What do river bank and riner bed mean/ Do they have the same meanings?
Ms Leung's response:
River banks are on the 2 sides of a river channel.
River bed is at the bottom of the channel.
Question 2:
回覆刪除Are Velocity and discharge the same?
Ms Leung's response:
Velocity: speed of river flow
Discharge: amount of river water
Question 3:
回覆刪除Why do the river sources have changes in only headward erosion?
Ms Leung's response:
There can be downcutting too at the river source. But there is too little water to do so.
Question 4:
回覆刪除If there is programme to prevent flooding at the middle course. How the features of the channel change?
Ms Leung's response:
Brilliant questioning mind :) Appreciated!
Yes, it'll be a heat question in public exam. We'll touch on it in unit 2.5. It'd be lovely if smart students can respond to this brilliant question. Try!
Question 5:
回覆刪除At the upper course, why does water concentrate on the shortest path?
Ms Leung's student:
We can tell that the student asking this question has a logical mind. Who'd like to try to answer this question, please?
Question 6:
回覆刪除How does soil erosion cause silting?
Ms Leung's response:
Let's see if any student can answer your question
Question 7:
回覆刪除What does the river sources look like?
Ms Leung's response:
A river source is usually a spring where underground water gets onto the ground surface.
Want to know how the source of Chang Jiang was found? Pls watch this video:
http://www.youtube.com/watch?v=9u3s6i-V2Qg
(for the river source: pls go straight to 2'15")
For a more details of a trip to "follow a river to the source"
http://www.youtube.com/watch?v=NH1IghSJwhE
(for the river source: pls go straight to 5'10")
Question 8: Where does the water come from the river sources?
回覆刪除Ms Leung's response:
李白不是說: 君不見黃河之水天上來嗎?
What do you think?
Question 9:
回覆刪除Are there any meander in Hong Kong?
Ms Leung's response:
There are only uuper and middle courses of rivers in HK. The lower course of rivers usually pass through urban areas / new towns, so they're all channelized , i.e. the river course is straightened. So we can't see mature meanders in HK.
Question 10:
回覆刪除If there are some obstacles on the channel, will this cause waterfall?
Ms Leung's response:
Obstales on the channel usually form turbulence. Rapids & potholes, etc are formed. Waterfalls are closely related to outcrops of resistant rocks.
Question 11:
回覆刪除Sometimes, the waterfall is not so high or straight, like the waterfall in 新娘潭, so how can we classify rapids and waterfall?
MsLeung's response:
Good question. Who can answer this question please?
Question 12:
回覆刪除What is the factor lead to the formation of delta?
Ms Leung's response:
There are 2 main factors for depostion:
1. Large amount of loads
2. Small amount of energy (river / sea)
Under what conditions will there be large amount of loads transported to the sea?
Under what conditions will there be smaller amount of river energy?
--> Who'd like to answer these 2 challenging questions?
Question 13:
回覆刪除During revision, I ve read Ch 2.3.
But I what I dont understand is that the lower course has the largest discharge overall = largest river energy, right?
However, the lower course favours deposition landforms.
Also, the upper course shall have the least river energy, but the major fluvial process is erosion.
Isnt that the larger the river energy, the more erosion occurs??
Why is there such phenomenon?
Ms Leung's response;
You have an inquiring mind. Appreciated :)
You have correct concept on the general relationship between river energy and fluvial processes. Clever girl !
I think you can pay attention to the following prinicples in studying relationship / correlation between X and Y.
1. If X is the cause and Y is the result,
you should note if X is the only cause.
--> Cause & effect are not linear usually.
--> There are often multiple causes and even mulitple effect.
For example, one of your queiry is, "If there is little energy in the upper course, why isn't there a lot of deposition?"
The conditions for deposition:
(1) Yes, little energy.
(2) Supply of sediments.
In the upper course, river water has just started running (starting from the source). There is not enough time and energy for erosion. So there is little supply of sediments. How can there be deposition? 無遮無扇,神仙都難變啦~
2. How can we define the major / dominating fluvial process? It is defined in terms of proportion, not in absolute amount.
For example, just for comparison (the following data are NOT true value):
Amount_______Upper course______Lower course
Discharge__________10______________1000
Erosion_____________7______________200
Transportation______2______________100
Deposition__________1______________700
(Assuming: 1. the units are the same; 2. The amount of fluvial processes equals to the amount of discharge.)
In terms of absolute amount, the lower course has the largest discharge, so all the fluvial processes are large in amount.
But in terms of proportion, in the upper course, the proportion of erosion is the largest. In the lower course, the proportion of deposition is the largest.
Q.4 If there is programme to prevent flooding at the middle course. How the features of the channel change?
回覆刪除Response by Chong Sum Ping:
The feature of the channel become straightened river banks become symmetric and river bed becomes smoother.
The speed of water flood increase natural erosion and the position decrease
transportation increase.
Advantage of flood prevention
Reducing the risk of flood along the middle and lower courses of the river is able to prevent the “once-a-century”(百年一遇) flood.
Disadvantage of flood prevention
Increase the risk in flooding in upper course threatens the safety in the lower courses regions is the dam collapses.
Q.6 How does soil erosion cause silting?
回覆刪除Response by Chong Sum Ping:
Soil erosion in the upper course will increase the sediment in the river. Thus, the transportation mainly takes place. When the river flows to a reservoir, where water is kept beyond the dam. As the river discharge is low, so deposition is the major process. Therefore, the sediment deposits on the river bed and thus silting takes place. This will raise the river level (river bed) and hence reduce the river capacity. Flooding will be more likely to happen.
Q.7 What does the river sources look like?
回覆刪除Response by Chong Sum Ping:
The river source gathers the water from tributaries
Q.8 Where does the water come from the river sources?
回覆刪除Response by Chong Sum Ping:
The water come from the ocean，the melting of snow and glacier and the
rainfall
Q.9 Are there any meander in Hong Kong?
回覆刪除Response by Chong Sum Ping:
I found that 新界北區梧桐河is an example of the meander
Q11 Sometimes, the waterfall is not so high or straight, like the waterfall in 新娘潭, so how can we classify rapids and waterfall?
回覆刪除Response by Chong Sum Ping:
Rapids is a section of fast-flowing, turbulent running water
Develop when there is hard rock dipping downstream.
The soft rock downstream is worn away more quickly, leaving the hard rock sticking up into the river channel.
Waterfall is a vertical fall of water in the water caused by abrupt change of the channel slope over a short distance
Q12 What is the factor lead to the formation of delta?
回覆刪除Response by Chong Sum Ping:
Removal of sediment is lower than deposition
There gentle slope near the shore
The water is shallow
Among of load is large
Questions of Ms Leung
回覆刪除Under what conditions will there be large amount of loads transported to the sea?
Response by Chong Sum Ping:
River flowing through an area composed of loose materials
Joining of tributaries
Active erosion in the upper course and on the river channel