***Didn't see this question otherwise would've answered quickly
Storm hydrograph is a graph used to show the relationship between rainfall & the subsequent water flow in a river.
Its shape varies from basin to basin but each has these features:
Approach segment- Shows water flow prior a rainfall. Water is not directly supplied to a river by the falling rain but from runoff.
Rising Limb- Steep rising limbs indicate water is entering a river fast.
Lag time- Shows the duration of water entry in a river when rainfall & discharge are at their highest (peak). (Short lag times means steep rising limb, therefore water entering fast; the reverse is true for long lag times.
Falling limb- slow discharge in a river