1.2 Hydrographs

Question 1

What are the factors which effect hydrographs?

Answer 1

Drainage Basin Characteristics
- Size
- Shape
- Drainage Density
- Relief

Human
- Landuse/urbanisation
- Deforestation
- Positive

Environmental
- Climate
- Vegetation
- Soil & Rock Type

Question 2

How does drainage basin size effect hydrograph

Answer 2

Small
- Lower overall discharge
- fast rising limb and falling limb - flashy
- flash floods

Large
- Higher overall discharge
- larger lag time
- less flashy

Question 3

How does drainage basin shape effect hydrograph

Answer 3

Circular
- Flashy, quick response time, smaller lag time
- meets one spot all at same time - high flood risk

Elongated
- Less flashy, longer lag time
- Doesnt meet all at same time

Question 4

How does drainage density effect hydrograph

Answer 4

Higher
- = more stream rivers etc
- therefore more overland flow moves faster overland
- faster lag time, flashy higher peak

Question 5

How does relief effect hydrograph

Answer 5

Steep
- Less infiltration as water can’t absorb because its moving (gravity)
- higher surface runoff
- flashier etc

Flat
- Inverse

Question 6

How does land use effect hydrograph

Answer 6

• Impermeable materials used = less infiltration
• more faster surface runoff
  -storm drains prevent too much surface runoff - but also flow quicker so increase peak discharge + more flashy

Question 7

How does deforestation effect hydrograph

Answer 7

• more overall discharge as less water is stored and transpired or evap
• faster flow due to less interception/stemflow/throughflow

Question 8

How does climate effect hydrograph

Answer 8

Temp
- Very hot = increased evptrn but can bake soils so less infiltration 20% more discgarge due to climate change
- Very cold = no infiltration - snow melt

Rainfall Intensity/type/duration

Question 9

How does rocktype effect hydrograph

Answer 9

Porous;
- Higher field capactiy

Permeable
- higher infiltration rate e.g. snad 3-12mm/hr vs clay 0-4mm/hr

Question 10

How does vegetation effect hydrograph

Answer 10

• Can store, 40,000 gallons in broadleaved beech trees a year in evapotranspiration
• slow down flow of water
• bare soils - o-10mm/hr due to rain splash vs 50-100mm/hr on vegetated

Question 11

Example; River Mole

Answer 11

• Tear drop shape - flash flood in 68

Question 12

Example; Indus

Answer 12

2010
- Glacial Melt
- Taliban deforested KPK valley until 2009

Question 13

Example; Lower Mersey

Answer 13

25% increase in urbanisation
lead to 25,000 properties in flood risk

Question 14

Example; River Valence Bodmin

Answer 14

2004
- Steep valley sides
- small catchment area