HELP: Don't understand FLOOD/STORM HYDROGRAPHS (AQA A GEOGRAPHY)Watch
The peak discharge refers to the highest point on the graph, when river discharge is at its highest.
The lag time is the delay between peak rainfall and peak discharge. The lag time shows the time taken for the water to flow into the river. A shorter lag time means that the river will reach peak discharge more quickly, because the water flows into the river more quickly.
The rising limb is the part of the graph leading up to peak discharge. The discharge increases as water flows into the river.
The falling limb is the part of the graph which is falling after peak discharge. The discharge decreases as less water is flowing into the river after the storm.
A storm hydrograph with a steep rising limb (a short lag time and high peak discharge) is known as a 'flashy' hydrograph.