Monday, April 6, 2009
1st April 2009
Hi all! Happy April Fool's Day! Sorry for the belated post for the 1st of April Geography Lesson with Mr. Faizal. Anyway, here it is:We started of on the revision of water balance, where Input = Output. Input consists of the precipitation and the Output consists of total streamflow (Q), evapotranspiration (E) and storage (S).
We then moved on to the section on Hydrographs. Basically, a hydrograph shows how a river reacts to rainfall. So there are 5 main sectors of the Hydrograph.
1) Antecedent flow rate
- This is the point before the rainfall effect starts and is at the start of the hydrograph
2) Rising Limb
3) Peak of the graph
- This part of the graph is known as the peak flow rate, where peak discharge is observed
4) Falling Limb
5) Groundwater recession
- After the rainfall, when the river's discharge is close to zero.
And there are other important details to remember in a hydrograph.
Firstly, the baseflow and stormflow. The storm flow is the sector of the graph between the rising limb and the falling limb and the baseflow is the sector of the graph between the Antecedent flow rate and Groundwater Recession.
Secondly, the bankfull discharge. The point of bankfull discharge is determined by calculations. If the graph goes above the bankfull discharge level, it means that the river experiences a flood.
And thirdly, the lag time. Basically, the lag time is the time between peak rainfall (Antecedent flow rate area) and peak discharge (Peak flow rate of graph)
We then evaluated how and why storm hydrographs differ. This is dependant on many factors, such as the rate of rainfall, amount of rainfall, and basins with impermeable bedrock.
The rate of rainfall determines the overland flow. If there is high rate of rainfall, there is high overland flow, resulting in dramatic hydrographs, with steep limbs and high peaks.
Less dramatic hydrographs occur when there is light, summer rain when evaporation rates are high and when discharge is easily absorbed.
Ok, so that's about it! I hope I didn't miss out much. Please add in comments too. See Ya!
Akshay