Hydrographs Flashcards
What do storm hydrograph show
How a river responds to a rainfall event (in a specific location)
Flashy hydrograph meaning
A hydrograph with a steep rising and falling limb and short lag time
Subdued hydrograph meaning
A hydrograph with a gentle rising and falling limb and a long lag time
Which type of hydrograph has a gentle rising and falling limb and long lag time
Subdued
Which type of hydrograph has a steep rising and falling limb and a short lag time
Flashy
8 physical factors that effect the shape of hydrographs
Drainage basin shape (circular vs long and thin)
Drainage basin relief
Drainage density (the number of tributaries there are)
Antecedent rainfall
Soil and rock type
Vegetation
Amount and intensity of precipitation
Drainage basin size (larger vs smaller)
How does drainage basin shape (circular vs long and thin) affect the shape of the hydrograph
Drainage basins more circular in shape mean that the water has a shorter distance to travel to reach a river so there is a shorter lag time which leads to flashy hydrographs
Long and thin drainage basins have a longer lag time as the water has to travel further to reach a river
Which out of circular and long and thin drainage basins have a shorter lag time and why
Circular
The water has less far to travel to reach a river compared to drainage basins that are long and thin so it reaches the river quickly and there is less time between when the precipitation fell and when the precipitation gets into the river
How does drainage density effect the shape of the hydrograph
A higher drainage density (a drainage basin with more tributaries relative to its size) leads to a short lag time and flashy hydrographs as the tributaries transfer the precipitation to the main river very quickly
How does the relief of the drainage basin affect the shape of the hydrograph
Steep sided drainage basins have shorter lag times than gently sloped drainage basins. This is because the force of gravity leads to less infiltration and more overland flow which transfers the water over the surface downhill very quickly and into the river.
How does antecedent rainfall affect the shape of the hydrograph
A high level of antecedent rainfall causes the drainage basin to become saturated. This means that less infiltration can occur and there is more overland flow so water enters the river very quickly leading to a short lag time
How does soil and rock type affect the shape of the hydrograph
Impermeable rock leads to increased overland flow and less through flow and infiltration so water enters the river very quickly. This causes a short lag time
How does vegetation affect the shape of the hydrograph
A large amount of vegetation (thick vegetation cover) intercepts precipitation so slows down the movement of water to the ground (and into the river) creating a longer lag time. Water from vegetation surfaces is also lost by evapotranspiration meaning that less water gets into the river and there is a lower peak discharge
How does the amount and instensity of the precipitation affect the shape of the hydrograph
Heavy storms (where the precipitation is intense and there is a large amount of it) mean that there’s a lot of water entering the drainage basin over a short period of time leading to increased overland flow as the soil becomes saturated. This creates a short lag time as the water enters the river very quickly. The high volume of rainfall also leads to a high river discharge
How does the size of the drainage basin affect the shape of the hydrograph
Larger drainage basins catch more precipitation than smaller drainage basins so have a higher peak discharge however they also have a longer lag time as the water has further to travel
How does agriculture affect the shape of hydrographs
Contour ploughing is where the plough follows the contour lines of the slope and high slows down the movement of water and encourages infiltration, hence reducing overland flow and creating a longer lag time.
Ploughing up and down a slope leads to fast overland flow via the furrows which creates a short lag time
How does deforestation affect the shape of the hydrograph
Deforestation means there are less trees to intercept the precipitation and there are less roots in the ground to create channels in the soil for s higher rate of infiltration. Therefore there is a lower rate of infiltration and high rate of overland flow creating a short lag time. Deforestation also causes the soil to become more exposed to the sun, making it more easily eroded which leads to sedimentation of the soil and an increased risk of flooding
How does growth of urban area affect the shape of the hydrograph
Urban growth leads to more impermeable surfaces (e.g roads and car parks made of tarmac) leading to a high rate of overland flow and short lag time as water cannot percolate into the ground. Most settlements have camber roads which are designed to transfer water away from the human activity and to the nearest river as quickly as possible, again creating a short lag time.
4 human factors that effect the shape of hydrographs
Deforestation
Afforestation
Agriculture
Growth of urban areas
Which type of ploughing is where the plough follows the contour lines of the slope
Contour ploughing
What is contour ploughing
Where the plough follows the contour lines of the slope
Which type of ploughing leads to a longer lag time
Contour ploughing
Which type of ploughing leads to a short lag time
Ploughing up and down
What is peak discharge
The maximum discharge of the river
What is peak rainfall
The highest amount of rainfall
What is lag time
The period of time between peak rainfall and peak discharge
What is raising limb
The period of time where the river discharge is rising
What is falling limb
The period of time where the river discharge is decreasing
