♥ 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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