Factors influencing hydrographs Flashcards
Name 5 factors that influence hydrographs
- Drainage basin size
- Drainage basin shape
- Vegetation type
- Gradient of valley
- Rock type
- Type and amount of precipitation
How does precipitation type influence a hydrograph?
Snow will cause a much larger lag time than rainfall as it takes a long time to melt, however will cause an increase in river discharge when it melts.
How does precipitation intensity influence a hydrograph?
More rainwater leads to more water in a river, therefore higher discharge
How does vegetation type influence a hydrograph?
If the area surrounding the river has thick vegetation cover then some precipitation will be intercepted, increasing the lag time.
Also peak discharge will decrease because vegetation will absorb water and lose it through evapotranspiration.
Coniferous trees intercept 25-35% of annual precipitation, deciduous trees intercept 15-25%. This increases lag time.
How does drainage basin size influence a hydrograph?
Large basins will have high peak discharges as they catch more precipitation.
However they also have longer lag times as the water takes longer to reach the rivers
How does drainage basin shape influence a hydrograph?
Circular basins will have a more flashy hydrograph as it will have a steep rising limb and high peak discharge.
This is because all points in the drainage basin are equidistant from the river, so water reaches the river at the same time
How does rock type influence a hydrograph?
If a river is surrounded by impermeable rock, it’s going to have a high peak discharge and short lag time. This is because overland flow is quicker than percolation
Also, these can’t store water so peak discharge is higher due to all water being in the river.
How does valley gradients influence a storm hydrograph?
Where gradients are steep, water runs off faster - reaching the river quicker. This causes a steep rising limb.
They will also have a short lag time as water can travel faster downhill
