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♥ Sunday, April 19, 2009 ♥
Sorry o3, totally forgot about this!
I'll be referring to the handout.
Page 230: Diagrams
If the shape of the drainage basin is as in the diagrams, then the gauging station is located at the bottom edge of the basin, in order to gauge the entire basin (if it was located at the middle, it would only gauge part of the drainage basin).
Hydrograph of Diagram 1:
-Short lag time
The highest discharge is at the bottom of the basin, due to the wider area and the large amount of tributaries.
Thus, the highest amount of discharge is within the "early" time zone (that is, it reaches the gauging station earlier), leading to an early peak.
Hydrograph of Diagram 2:
-Long lag time
The highest discharge is at the top of the basin, as there is a larger area at the top, so it collects more rainwater.
Thus, the highest amount of discharge is within the "late" time zone (that is, it reaches the gauguing station later), leading to a late peak.
Hydrograph of Diagram 3:
-Double lag time
There are two areas with the highest discharge, one at the top and one at the bottom of the basin, due to the wider areas here.
This leads to a double-peak as the two main discharges reach the gauging station at two different times.
Soil and water:
Base flow comes below the soil
Throughflow comes through the soil
Overflow comes above the soil
Ground water is below the soil and acts like a store of water (it is just above a rock layer), which is a long-term store (as opposed to surface water bodies) and can last for millennia. It is the source of water for wells. It is due to the fact that some rocks are quite porous and can "hold" water after it comes down through percolation, which comes after infiltration.
Throughflow is a less consistent store of water, as opposed to ground water, and it is faster than baseflow. It occurs through infiltration of water through the soil.
Baseflow is slower than throughflow, but it is more consistent than it, since it draws from ground water stores.
The drainage density of a basin is related to the efficiency of the flowing of water (or something like that). The higher the density, the more efficient the flow of water is, leading to a shorter lag time, and vice versa.
A bit on Pg 230, regarding the shape of the basin:
Long basin
-Consistent amount of water
-Early and late time zones both produce the same amount of water.
-Thus, there is an extended peak, as the water does not come all at once.
Round basin
-The discharge reaches the gauging station at around the same time.
-This leads to a short but sharp peak.
Calvin
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♥ Wednesday, April 8, 2009 ♥
Firstly I would like the emphasize that in this post, I would not post pictures/excerpts from our geog textbook as I think it is redundant to do so since it isn't that hard to refer to your geog textbook.
To start things off:
Mr Faizal was once again explaining to us about the water balance because we were unsure about it. This time, he drew a diagram so I took it down...note that not all aspects of the water balance are illustrated here.
Storm Hydrograph:
(enlarge the photo to have a closer view)
This one caused quite abit of a stir...
- Lag time: When a rain drop falls, the water level of a river does not shoot up immediately due to drainage. A rain drop still has to go through various processes occur before the water reaches the river. An example would be...imagine that you are a raindrop( so fun! ) and you precipitated down to earth. You land on the soil and infiltrate it. Thereafter, you would percolate and via throughflow, you reach the river. Hence, from this you can see, time was needed for the water to reach the river. This is lag time. Something to take note, a drainage basin with a steeper profile has less lag time and a drainage basin with a gentler profile has a longer lag time due to the speed at which the water reaches the river.
- Rising Limb: After some time, water from the drainage basin would arrive at the river and it's water level thus rises.
- Max. Capacity: When the river reaches it's maximum capacity and water is still flowing towards it, the river overflows its banks.
- Recession Limb: When it stops raining(precipitating) some water within the drainage basin which hasn't reached the river continues its journey to the river. After which, the water level of the river slowly recedes and this is reason for the recession limb.
- Rainfall Chart: The graph of the rainfall.
Yayy hope you understood it xD
Done by.. me. (:
Chunwai.
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This picture shows a typical meander along the grassland. Notice that the grassland is much flatter and wider than the valley along the upper course. :)
The picture shows a floodplain, which is flat or nearly flat, and is adjacent to a stream or river. This position causes it to be flooded occasionally. :)
