Hydrographs

• a hydrograph measures the amount of water flowing through a river or stream over a period of time
• on a hydrograph- if there is a steaper rising limb- it means there is an impermeable surface, if it is a flat limb- it means there is a permeable surface
• the peak flow is the highest point on the graph
• Lag time is the time it takes for the channel to reach peak discharge following peak rainfall
• lag time is long (subdued) when the water slowly drains through surfaces
• lag time is fast (flashy) when it drains through drains and sewers
• rainfall is presented in bars on the graph