Influences on Hydrographs

Question 1

What are the factors affecting storm hydrographs?

Answer 1

• length/intensity/type of pptn
• soil type + depth
• urbanisation
• agri.
• (forest) veg.
• drainage basin density/size/shape
• relief
• rock type
• lakes + reservoirs
• grassland + moorland
• deforestation

Question 2

Drainage basin density

Answer 2

• higher density = shorter lag time + greater peak discharge
• shorter lag time: shorter distances rainfall has to travel to reach river

Question 3

Drainage basin size

Answer 3

• larger basin = higher peak discharge + longer lag time
• bc collects water from larger area so more enters river
• longer lag time: water has to travel larger distance to reach river

Question 4

Drainage basin shape

Answer 4

• circular basin (not elongated) = shorter lag time + higher peak discharge
• bc less time for water to reach channel as all extremities are roughly equidistant from channel

Question 5

Relief

Answer 5

• steeper = shorter lag time + higher peak discharge
• bc water reaches river more quickly as water travels more quickly downhill

Question 6

Rock type

Answer 6

• impermeable rocks = shorter lag time + higher peak discharge
• bc doesn’t allow percolation (saturated quickly) so more throughflow + overland flow
• permeable rocks:
  
  • porous (sandstone + chalk): contains pores able to fill w + store water
  • pervious (limestone): allows water to flow along bedding planes + down joints in rock

Question 7

Length of pptn

Answer 7

• prolonged pptn: shorter lag time + higher peak discharge
• bc ground is saturated + infiltration replaced by overland flow (flooding may occur)

Question 8

Intensity of rainfall

Answer 8

• intense/heavy rainfall: shorter lag time + higher peak discharge
• bc intensity > soil infiltration capacity: overland flow inc.

Question 9

Type of pptn

Answer 9

• heavy snowfall: lag time longer + peak discharge lower
• bc water is held in storage + when temp rises snow melts + infiltration capacity is exceeded or ground is frozen + overland flow inc.

Question 10

Soil type

Answer 10

• sandy soils: longer lag time + peak discharge dec.
• bc large pore spaces have high infiltration capacities + allow rapid infiltration
• clay soils: shorter lag time + peak discharge inc.
• bc smaller pore spaces have low infiltration capacities + allow little infiltration

Question 11

Soil depth

Answer 11

• thin soils: shorter lag time + peak discharge inc.
• bc stores small amounts of water: saturated quickly + inc. throughflow + overland flow

Question 12

Vegetation

Answer 12

• soils under forested areas: longer lag time + peak discharge dec.
• bc have high infiltration capacities: inc. infiltration rates + allows more throughflow

Question 13

Forest vegetation

Answer 13

• inc. forest veg: longer lag time + peak discharge dec.
• bc high lvls of interception: inc. water in drainage basin + slows flow to river + allows inc interception loss so less water entering river
• in winter: trees deciduous so less interception + higher discharge

Question 14

Urbanisation

Answer 14

• more urbanisation: shorter lag time + peak discharge inc.
• bc less permeable surfaces so inc. surface runoff + drains carry water quickly to rivers

Question 15

Deforestation

Answer 15

• more deforestation: shorter lag time + peak discharge inc
• bc less surface storage + interception so less evapotranspiration + more surface runoff

Question 16

Grassland + moorland

Answer 16

• more grassland + moorland: shorter lag times + peak discharge inc.
• bc lower veg. densities: less interception loss + soil infiltration + moisture capacity lower so inc. overland flow