Factors affecting the storm hydrograph

Question 1

Area

Answer 1

large basins receive more precipitation than small basins therefore have larger run off and have larger lag time.

Question 2

Shape

Answer 2

elongated basins will have a lower peak flow and longer lag time than a circular one

Question 3

Relief

Answer 3

in steep upland valleys water reaches the river more quickly as water flows faster down a steep slope. Rising limb is steeper and lag time shorter in steep sided valleys.

Question 4

Rock type

Answer 4

Permeable rocks like limestone will means rapid percolation, so little surface run off. Impermeable rocks like granite do not allow percolation so there is no storage, resulting in a steep rising limb and high peak discharge.

Question 5

Soil Type

Answer 5

Sandy soils have larger pore spaces to allow rapid infiltration. Clays have much smaller pore spaces reducing infiltration capacity. The more infiltration that occurs, the longer the lag time and the gentler the rising limb.

Question 6

Land Use

Answer 6

in urban areas with large proportions of tarmac and other impermeable surfaces, drains ensure that water reaches river very quickly, resulting in a steep rising limb and short lag time.

Question 7

Precipitation and Temperature

Answer 7

Short intensive rainstorms can produce rapid overland flow giving a steep rising limb. Extreme temperatures can result in the ground being hard (either baked or frozen) again causing rapid surface run off.

Question 8

Type of precipitation

Answer 8

Flooding most frequently occurs after long periods of heavy rain, when the ground has become saturated and infiltration has been replaced by run off. Heavy snowfall means that water is stored and river levels drop. When temperatures rise and thaw sets in, melt water reaches river quickly.