Wc10 - flood hydrograph

• flood hydrograph


  graph that shows how discharge changes over time
• discharge


  the quantity of water in a stream that passes a given point in a period of time
• peak rainfall


  the greatest amount of rainfall that falls in a storm
• rising limb


  the period of rising river discharge following a period of rainfall
• lag time


  time between peak rainfall and peak discharge
• peak discharge


  the greatest volume of water that flows in the river at a given time
• falling limb


  the decrease in river discharge as the river returns to its normal level
• base flow


  normal discharge of the river
• bank full discharge


  the maximum discharge a river can hold before the water overflows its banks
• storm flow


  discharge resulting from storm precipitation involving both overland flow, throughflow and groundwater flow
• how does the shape of drainage basin cause variations in the flashiness of a flood hydrograph?


  -circular means water arrives in the river at similar times -> flashy hydrograph

  -long and thin means water arrives at different times -> low, flat hydrograph
• how does drainage basin relief cause variations in the flashiness of a flood hydrograph?


  -steep gradient means water is funnelled quickly into river -> flashy hydrograph

  -gentle gradient means water slowly flows into river -> low, flat hydrograph
• how does drainage density cause variations in the flashiness of a flood hydrograph?


  -high drainage density means water arrives in the river at the same time -> flashy hydrograph

  -low drainage density means less water arrives at the same time -> low, flat hydrograph
• how does antecedent soil moisture cause variations in the flashiness of a flood hydrograph?


  -saturated soil means overland flow is increased and lag time is reduced -> flashy hydrograph

  -unsaturated soil means infiltration capacity has not been reached so overland flow is reduced -> low, flat hydrograph
• how does geology cause variations in the flashiness of a flood hydrograph?


  -impermeable rock means overland flow is high -> flashy hydrograph

  -permeable rock means overland flow is low -> low, flat hydrograph
• how does vegetation cover cause variations in the flashiness of a flood hydrograph?


  -little vegetation means low levels of interception, so increased overland flow -> flashy hydrograph

  -thick vegetation means high levels of interception so decreased overland flow -> low, flat hydrograph
• how does size of drainage basin cause variations in the flashiness of a flood hydrograph?


  -large drainage basin catches more precipitation so higher peak discharge -> flashy hydrograph

  -small drainage basin catches less precipitation so lower peak discharge -> low, flat hydrograph
• how does deforestation cause a flashy hydrograph?


  -reduced vegetation reduces interception, so rain directly hits surface leading to rapid overland flow -> flashy hydrograph
• how does urbanisation cause a flashy hydrograph?


  -increased impermeable surfaces reduces infiltration and increases overland flow -> flashy hydrograph
• how does size of drainage basin cause variations in the flashiness of a flood hydrograph?


  -grazing animals remove roots from soil which reduces infiltration and increases overland flow -> flashy hydrograph

  -ploughing breaks up topsoil and leads to greater infiltration -> low, flat hydrograph
• how do flood management schemes cause variations in the flashiness of a flood hydrograph?


  -reservoirs release water quickly leading to rapid rise in river discharge -> flashy hydrograph
• how does water abstraction cause a low, flat hydrograph?


  -water flowing downstream is reduced, leading to lower base flow levels