The shape of a storm hydrograph is affected by several factors including the size and steepness of the river basin, weather conditions, vegetation cover, rock type, drainage density, and level of urbanization. Smaller river basins with steeper slopes will have shorter lag times as water drains from the land into the river more quickly, while heavy rainfall and saturated ground from prolonged rain increase the amount of surface runoff entering the river. Vegetation and permeable rocks can absorb more water and reduce runoff, whereas impermeable surfaces and efficient drainage systems in urban areas decrease lag time.

1. Storm hydrograph
Thingsthat affectthe shape of the storm hydrograph
Size andshape of the riverbasin – the smallerthe basinthe lesstime ittakesthe rivertodrain so there isa shorter
lag time.The steeperthe riverthe quickerittakestodrain the water.
Weather– heavystormsmeansthat waterdoesn’thave time to infiltrate intothe soil causinglotsof surface runoff.
A lengthyrainfallcausesthe groundtobecome saturatedandthisalsoincreasessurface runoff.
Vegetation –thisinterceptsthe precipitationandaddstorates of evapotranspirationwhichreduces the through
flowasthe rootstake upwater.It isincreasinglycommoninwinterforthere tobe lotsof floodsbecause treesand
plantslose theirleaves.
Rock type – permeable rockslike chalkmayabsorbwaterwhilstimpermeablerocksencourage greater amountsof
surface runoff leadingtoamuch more rapid discharge.
Drainage density –the higherthe drainage density resultsin increasedriskof flooding asthere are more tributaries
and streams.
Urbanisation – impermeable surfaceslikeconcrete andtarmacincrease surface runoff aswell asdrainage systems
helpwaterreachthe riverquickerwhichdecreasesthe lagtime.