Flashcards in Storm Flood Hydrograph 3112 Deck (21):
What is a storm hydrograph?
A graph of the discharge of w river leading up to and following a storm or rainfall event
Why are storm hydrographs useful?
They can predict how a river might respond to a rainstorm and this can help in managing the river.
What is base flow (on a storm hydrograph)?
This is the water that feeds the river by through flow of soil water and groundwater. These movements are slow and therefore means that the changes in the discharge are small.
What happens as storm water begins to enter the drainage basin?
The river beings to be fed by much faster moving water. The discharge rises as shown by the rising limb of the storm hydrograph. It eventually reaches a peak discharge the highest flow in the channel for that event.
What is lag time?
The time taken from peak rainfall to peak discharge.
What a receding limb show?
It shows that discharge is beginning to fall
What happens to the river once all the storm water once is has passed though??
It returns to its base flow.
What is a flashy storm hydrograph?
One that has a short lag time, high peak discharge, steep rising and falling
What is a subdued hydrograph?
One with gentle rising and falling limbs, long lag times and low peak discharge.c
What are the physical factors affecting the shape of a storm hydrograph?
1) shape of drainage basin
2) relief of basin
3) drainage density
4)soil or rock type
5) vegetation cover
6) amount and intensity of precipitation
7) size of the drainage basin
How does the shape of the drainage basin affect the shape of the storm hydrograph?
Drainage basins that are more circular in shape lead to more flashy than those that are long and thin this is because each point in the drainage basin is roughly equidistant from the measuring point in the river.
How does relief of s drainage basin affect the shape of a hydrograph??
Drownings basins with steep sides have flashy hydrographs as water flows more quickly on the steep slopes as through flow or overland flow so gets to the river more quickly
How does vegetation cover affect the shape of a storm hydrograph?
Thick vegetation cover in drainage basins will have a significant effect, vegetation intercepts the precipitation, holding the water on its leaves lowing the movement of rainwater to the ground and so the river channels - water is lost through evapotranspiration from vegetation surfaces reducing how much gets to the river and increasing lag time
How does amount and intensity of precipitation affect the shape of a storm hydrograph?
Heavy storms with a lot of water entering the basin in a shirt a ain't of time result in higher discharge. The type can also have an impact the lag time is likely to be greater if the precipitation is snow as snow takes time to melt before the water enters the channel - when there is rapid melting of snow the peak discharge could be high
How does the size of the drainage basin affect the shape of storm hydrographs?
Larger basins catch more precipitation and so have higher peak discharge compared to smaller basins. Smaller basins generally have shorter lag times be chase precipitation does not have as Fargo travel
Human reasons that shape a storm hydrograph?
4) urban areas
5) soft engineering
6) water abstraction
How does deforestation affect the shape of a storm hydrograph?
Reduces interception rates allowing rainwater to hit the surface directly & lack of roots reduces infiltration rates into the soil. Deforestation also exposes the soil to greater rates of erosion =sedimentation of the channel and reduces bank full capacity and therefore there is a greater chance of flooding.These both lead to flashy hydrographs
How does afforestation shape a storm hydrograph?
Increases infiltration and interception rates slowing the down the progress of water to the rove channel and subdues any changes in discharge
How does agriculture shape a storm hydrograph?
-ploughing breaks up the topsoil and allows greater infiltration, subduing hydrographs
- grass crops increase infiltration and lead to subdued hydrographs
How do urban areas shape storm hydrographs?
- growth of impermeable surfaces lead to flashy floods
- settlements are designed to transfer water as quickly as possible away from human activity and to the nearest river. In the uk there has been a continued loss of front gardens in favour of paved drives due to growing 2/3 car families.