Potential factors which can impact upon the flood hydrograph
What is a flood hydrograph?
A graph that shows how a drainage basin system responds to a period of rainfall. They show how long it takes after a rain storm has started for a river to reach its peak flow.
different hydrographs and make assumptions on the characteristics of a drainage system.
GEOLOGY
The rock type can have a significant effect on the flood hydrograph. Impermeable RELIEF (SLOPE)
catchments cannot store as much water. There is more surface runoff, therefore If a catchment has very steep sides then the water will have less t
the water reaches the river quickly, resulting in a shorter lag time, and a higher into the soil and there will be more increased overland flow. This
peak discharge. The rising limb will also be steeper. water reaching the river channel faster. There will be a short
If a catchment is permeable, more water can be stored and percolate through the If the basin is very shallow, the water will have more time to inf
rock. Therefore it takes longer for the water to reach the river, leading to a longer stored on the surface, therefore the lag time will be lo
lag time.
LAND USE/HUMAN ACTIVITIES
How land has been used can have a significant impact. If a land ha
TEMPERATURE to urbanisation, then the surfaces become impermeable. This le
High temperatures throughout the year would lead to higher rates of evaporation infiltration, more surface runoff or overland flow, a steeper rising li
and evapotranspiration. This would lead to more water in the atmosphere and peak discharge. Drains, guttering and roofing can also increase th
the development of thunderclouds, leading to more intense precipitation. water reaches the river. Different types of farming practises can
impact on the flood hydrograph. The direction in which farmers
fields can either increase or decrease the speed at which water rea
ANTECEDANT CONDITIONS VEGETATION
The conditions prior to a storm can impact the flood hydrograph. If there has Catchments that are heavily vegetated will have more interceptio
been a lot of rain before the storm event, then the ground will already be vegetation storage. These catchments will be able to store more
saturated. This means that no more water will be able to infiltrate and be stored catchments that have been deforested. Therefore deforested catc
in soil water storage. There will be more overland flow, a steeper rising limb, have an increased level of surface runoff, leading to higher peak
shorter lag time and overall a more “flashy” hydrograph. steeper rising limbs and shorter lag times.
What is a flood hydrograph?
A graph that shows how a drainage basin system responds to a period of rainfall. They show how long it takes after a rain storm has started for a river to reach its peak flow.
different hydrographs and make assumptions on the characteristics of a drainage system.
GEOLOGY
The rock type can have a significant effect on the flood hydrograph. Impermeable RELIEF (SLOPE)
catchments cannot store as much water. There is more surface runoff, therefore If a catchment has very steep sides then the water will have less t
the water reaches the river quickly, resulting in a shorter lag time, and a higher into the soil and there will be more increased overland flow. This
peak discharge. The rising limb will also be steeper. water reaching the river channel faster. There will be a short
If a catchment is permeable, more water can be stored and percolate through the If the basin is very shallow, the water will have more time to inf
rock. Therefore it takes longer for the water to reach the river, leading to a longer stored on the surface, therefore the lag time will be lo
lag time.
LAND USE/HUMAN ACTIVITIES
How land has been used can have a significant impact. If a land ha
TEMPERATURE to urbanisation, then the surfaces become impermeable. This le
High temperatures throughout the year would lead to higher rates of evaporation infiltration, more surface runoff or overland flow, a steeper rising li
and evapotranspiration. This would lead to more water in the atmosphere and peak discharge. Drains, guttering and roofing can also increase th
the development of thunderclouds, leading to more intense precipitation. water reaches the river. Different types of farming practises can
impact on the flood hydrograph. The direction in which farmers
fields can either increase or decrease the speed at which water rea
ANTECEDANT CONDITIONS VEGETATION
The conditions prior to a storm can impact the flood hydrograph. If there has Catchments that are heavily vegetated will have more interceptio
been a lot of rain before the storm event, then the ground will already be vegetation storage. These catchments will be able to store more
saturated. This means that no more water will be able to infiltrate and be stored catchments that have been deforested. Therefore deforested catc
in soil water storage. There will be more overland flow, a steeper rising limb, have an increased level of surface runoff, leading to higher peak
shorter lag time and overall a more “flashy” hydrograph. steeper rising limbs and shorter lag times.
