Braided Channels and Deltas
Ok, this is my first blog entry and may be my last post also (unless we have 22 more lessons :D).
Today lesson, we've come up with two concepts: braiding and deltas. Now I'm going to do some recap for you guys.
1) Braiding:
- A braided channel is a river within which the stream is divided into smaller and interlacing channels by small islands called "bars". (the picture looks like a bunch of epidemal cells, really)
- These bars are sediments deposited by the river and are very firm (in Bangladesh, people make use of these islands to build house on) because when old sediments are removed, new ones will arrive and be deposited at the bars
- Causes of this braiding features:
+ The river banks are easily eroded (materials from the banks will form the bars)
+ The more abundant the sediments are, the bigger and more of bars will be formed
+ If the river's discharge changes, formation of bars also changes. If less discharge, the river's velocity as well as its ability to transport sediments decrease and vice versa.
+ It also depends on the gradient of the river, if it's steep, velocity of water is greater and hence less deposition occurs. If the water flows more slowly, materials are easily dropped along the way.
2) Deltas:
- When a very large amount of sediments is deposited at the river mouth, materials will be piled up and new lands are formed here. These lands are called "delta".
- The river then has to divide to smaller channels called "distributaries" to overcome these blocks
- There are two types of Delta: arcuate and bird's foot (why not bird's feet???) but since (Miss) Peixin didn't say anything about them so i'm not going to mention here.
Extra stuffs about Delta:
Introduce you guys to the largest Delta in Vietnam!!! We call it "Đồng bằng sông Cửu Long", as translating to English, it'd mean "Nine Dragons river delta":
This Delta is formed at the mouth of the Mekong River. As you can see in the picture, the river itself has divided into 9 (nine) (:D) distributaries, that's why it's called "Nine-dragons...". In this area, people rely heavily on agricuture due to the rich of alluvium brought by the river.
OK that should be it :) Before i end my entry and go mug Chem stuffs, i want to remind you of the contents tested in assessment paper:
+ Atmosphere: - Climates, seasons
- Climograph
- Heat balance (no need to remember all the numbers but if you want to challenge your brain, then go ahead :D)
- Rain formation (adiabetic coolings, movement of air, types of rains)
* No global warming stuffs
+ Hydrophere: - Hyrpgraph
- Drainage basin (not sure about this)
- River channels processes
- Formation of waterfall
- River's features.
OK done! Have fun! :)
OK that should be it :) Before i end my entry and go mug Chem stuffs, i want to remind you of the contents tested in assessment paper:
+ Atmosphere: - Climates, seasons
- Climograph
- Heat balance (no need to remember all the numbers but if you want to challenge your brain, then go ahead :D)
- Rain formation (adiabetic coolings, movement of air, types of rains)
* No global warming stuffs
+ Hydrophere: - Hyrpgraph
- Drainage basin (not sure about this)
- River channels processes
- Formation of waterfall
- River's features.
OK done! Have fun! :)
Vu Ngoc Quang (aka CT rep :D) 5/5/2009
posted by 08ip01 at
8:03 PM
5 Comments:
Deltas are really fertile due to the high mineral content from the sediments, and in many countries farmers grow their crops in these areas. However, deltas are 'fragile'too. Because they are composed of layers of sediments, they erode very quickly. When people build dams, for example, it generates clean electricity. But as the river flow is reduced less sediment gets deposited, and over time the deltas erode away.
This will of course have implications on the ecosystem at the river.
This reminds us that every action we do will always have an effect of the enviroment. And we must always consider not just short-term, but also long-term implications so our decisions can be informed.
it sounds a bit strange to me...if, as Quang said, the small islands are formed by eroded material from the river banks, how come they clump together in the middle of a river instead of just being swept away? Maybe you could have addressed this
When the river reaches downstream it has loss of energy. This leads to deposition of the material the river has eroded in upstream. The material deposited by river leads to formation of small islands in the mouth of river which is known as Delta. The worlds biggest delta is formed by Ganges and Brahmaputra in Bangladesh which is known as Sunderbans.
Like what Victoria mentioned, our actions will have a consequence. Because of our thirst for power to quench our thirst for advancement, we harness energy from all sources humankind can reach out to, like Biofuels, Nuclear power, fossil fuels, and even building dams, tapping into Hydroelectric power.
These actions do affect the world in one way or another, often negatively. Have we actually sat down and reflected on whether technological advancement has indeed accelerated mankind's progress? The usage of laptops is prevalent in today's world, but research has been proven that prolonged usage will cause decrement of sperm growth. In extreme cases, it might even cause impotency. With new and more powerful laptops, wont the effects be more obvious? This is just one of avalanche of new problems arising from technological advancement. Many more problems has already plagued our society. It is high time that we rethink mankind's course of action.
I think that the reason that the small islands do not get washed away is that as the river has low energy, when it 'faces' the island, it does not have enough energy to overcome this obstacle, and instead, may dump some of it's sediments onto it, increasing the size of the island rather than decreasing it. I think =D
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