river regime & hydrographs

Define discharge of a river

The amount of water passing a specific point on the river at any given time

What is a river regime

A record of the changes in river discharge over a year

What is a storm hydrograph

A graph showing the change in river discharge after a storm event, usually a short period e.g 24 hrs

What part of the storm hydrographic is labelled as A and what does it show

• rising limb

• Shows the increase in river discharge after

• Steeper the rising limb → faster the river discharge increased

What part of the storm hydrographic is labelled as B and what does it show

• peak rainfall

• The highest rainfall level during the storm (time taken from middle of bar)

What part of the storm hydrographic is labelled as C and what does it show

• Lag time

• Time difference between peak rainfall and peak discharge

• Shorter lag time → higher risk of flooding

What part of the storm hydrographic is labelled as D and what does it show

• peak discharge

• Highest level of river discharge

What part of the storm hydrographic is labelled as E and what does it show

• recessional limb

• The river discharge returning to normal flow

• The faster the limb → the quicker the river returns to normal

What part of the storm hydrographic is labelled as F and what does it show

• base flow

• The normal level of river discharge

How can climate affect river regimes

• High temps → ice + snow melt → higher discharge

• High temps → increase evaporation → lower discharge

• High rainfall → increases river discharge

How can vegetation affect river regimes

• vegetation growing → obstacles for water (interception) and water moves slower → increases infiltration → decreases river discharge

How can land use affect river regimes

• concrete and tarmac in urban areas → impermeable so increases surface runoff or water is taken by drainage systems to river → increases river discharge

How can geology affect river regimes

• permeable rocks → increases infiltration → decreases river discharge

• Impermeable rocks → decreases infiltration → increases river discharge

How can soil affect river regimes

• soft soil → increase infiltration → decrease river discharge

• hard, compacted, frozen soil → decrease infiltration → increase river discharge

How can abstraction, dams and reservoirs affect river regime

• abstraction means water taken for irrigation → decreases river discharge

• Dams control the flow of water → can both increase and decrease river discharge

• Reservoirs experience higher levels of evaporation → decrease river discharge

How can relief affect river regimes

• Steep slopes → increase surface runoff as water travelling fast → increase river discharge

How can drainage density affect river regimes

• high drainage density → increased river discharge