L4 - Fast and Furious? Flashcards
What are the features of a storm hydrograph?
Rising limb - water level rising after rainfall
Lag time - time between precipitation falling and river containing most amount of water (peak discharge)
Falling limb - discharge falling
What factors affect storm hydrograph shape?
Precipitation, geology, basin shape and size, soil, vegetation, towns/cities, antecedent conditions
How do precipitation and geology affect storm hydrograph shape?
Precipitation - more means higher peak discharge due to the volume of water, vice versa
Geology - impermeable rock means higher peak discharge due to high surface run off, vice versa (permeable rock can hold some water decreasing peak discharge)
How does the basin shape/size affect storm hydrograph shape?
Large basin - high discharge
Small basin - rainfall reaches river quickly
(Both ^ result in high peak discharge)
Circular basin rather than elongated, water reaches source slower and gives lower peak discharge
How does soil affect storm hydrograph shape?
Saturated or frozen soil can hold little water so there is more surface run off making the peak discharge higher.
Dry soil can absorb more water reducing peak discharge and increasing lag time
How does slope gradient as soil depth affect storm hydrograph shape?
Steep slope and thin soil - rapid surface run off - higher peak discharge
Gentle slope and deep soil - slower surface run off - lower peak discharge
How do antecedent conditions affect storm hydrograph shape?
If there has been previous high rainfall, infiltration is reduced and new rainfall causes high surface run off and high peak discharge
If there hasn’t been rainfall, more water can permeate the soil to be absorbed and there is lower surface run off.
How do towns and cities affect storm hydrographs?
Urban - less permeable roads - higher peak discharge
Rural - permeable surfaces, more soil permeation - surface run off reduced
