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Water And Carbon Cycle > Flood Hydrograph > Flashcards

Flood Hydrograph Flashcards

1
Q

Define Hydrograph

A

A graph that shows river discharge and rainfall over time

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2
Q

Define Flood

A

When the capacity of a river to transport water is exceeded and water flows over its banks

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3
Q

Define Base Flow

A

The normal day to day discharge of the river and is the consequence of groundwater seeping into the river channel

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4
Q

Define Bankfull Dischatge

A

The maximum discharge that a particular river channel is capable of carrying without flooding

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5
Q

Define Peak Discharge

A

The point of a flood hydrograph when rainfall is at its greatest

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6
Q

Define Lag Time

A

Period of time between the peak rainfall and peak discharge

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7
Q

Define Peak Rainfall

A

The point on the flood Hydrograph when rainfall is at its greatest

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8
Q

Define Falling Limb

A

The fall in discharge back to base level

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9
Q

Define Rising Limb

A

Discharge rates increasing when storm water enters the drainage basin

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10
Q

How long does flood Hydrograph show?

A

Covers a relatively short time period usually days or hours

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11
Q

True or False? The shape of a Hydrograph varies in each river basin and each individual storm event

A

True

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12
Q

What are the physical features of the Drainage Basin which affects Flood Hydrographs?

A
  • Basin size
  • Drainage density
  • Rock type
  • Land use
  • Relief
  • Soil water
  • Rainfall intensity
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13
Q

What are the different types of flood Hydrograph and what are their characteristics?

A
  1. flashy = short lag time, high peak, steep rising + falling Limb (fast response = high discharge)
  2. Subdued = long lag time, low peak, gently rising and falling limbs (slow response = lower discharge)
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14
Q

What type of Basin Size creates a “Flashy” Hydrograph and why?

A

Small basin, as it leads to rapid water transfer

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15
Q

What type of Basin Size creates a “Subdued” Hydrograph and why?

A

Large basin, as it leads to a relatively slow water transfer

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16
Q

What type of Drainage Density creates a “Flashy” Hydrograph and why?

A

High density, speeds up water transfer

17
Q

What type of Drainage Density creates a “Subdued” Hydrograph and why?

A

Low density, slows down water transfer

18
Q

What type of Rock Type creates a “Flashy” Hydrograph and why?

A

Impermeable rocks - encourages rapid Overland flow with less slower throughflow and infiltration

19
Q

What type of Rock Type creates a “Subdued” Hydrograph and why?

A

Permeable rocks = encourages slow transfer by Overland flow with more throughflow and infiltration

20
Q

What type of Relief creates a “Flashy” Hydrograph and why?

A

Steep slopes = leads to rapid water transfer

21
Q

What type of Relief creates a “Subdued” Hydrograph and why?

A

Gentle slopes = slow down water transfer

22
Q

What type of Soil Water creates a “Flashy” Hydrograph and why?

A

Saturated soil = leads to rapid water transfer

23
Q

What type of Soil Water creates a “Subdued” Hydrograph and why?

A

Dry soil = soaks up water and slows down its transfer

24
Q

What type of Rainfall Intensity creates a “Flashy” Hydrograph and why?

A

Heavy rain = exceeds the infiltration capacity of vegetation and leads to rapid Overland flow

25
Q

What type of Rainfall Intensity creates a “Subdued” Hydrograph and why?

A

Light rain = transfers water slowly

26
Q

Human factors affecting Flood Hydrographs include?

A
  • Urbanisation
  • Drainage Systems
  • Water Abstraction
  • Afforestation
27
Q

Define Water Abstraction

A

Taking water from a ground source

28
Q

Define Afforestation

A

The establishment of a forest on land where there was no previous tree cover

29
Q

How does (no) urbanisation create a “Flashy” Hydrograph?

A
  • urbanisation used

- concrete surfaces (impermeable) increases Overland flow and reduce infiltration

30
Q

How does (no) urbanisation create a “Subdued” Hydrograph?

A
  • no urbanisation (rural environment used)

- no concrete surfaces (impermeable) so no increase in Overland flow and no reduction in infiltration

31
Q

How does (no) Drainage basin create a “Flashy” Hydrograph?

A
  • Drainage Basin in place

- leads to short lag time and higher peak discharge as water cannot evaporate or infiltrate into the soil

32
Q

How does (no) Drainage Basin create a “Sudued” Hydrograph?

A

No drainage basin in place

- longer lag time, and lower peak discharge as water can evaporate or infiltrate into the soil

33
Q

How does water Abstraction affect the Flood Hydrograph?

A

Reduces the base flow so more water must reach the channel before it reaches bankfull capacity

34
Q

How does (no) Afforestation create a “Flashy” Hydrograph?

A
  • no Afforestation in place
  • interception not increased
  • evapotranspiration does not increase
35
Q

How does (no) Afforestation create a “Subdued” Hydrograph?

A

Afforestation in place

- interception is increased and evapotranspiration increases, reducing how much water reaches river

36
Q

Why are Flashy Hydrographs more likely in urban areas?

A
  • more likely in urban areas as there is predominantly impermeable surfaces
  • this increases Overland flow due to removal of top soil and vegetation (reduces infiltration)
  • Drainage leads to rapid transportation of water into river channels which reduces lag time
  • For example, in winter of 2015/16 there were floods in Lake District and rivers responded quickly to heavy rainfall events, due to saturated soil conditions and steep slopes which meant water moved rapidly Overland and along river channels
37
Q

Why are Subdued Hydrographs more likely in rural areas?

A
  • rural areas have predominantly permeable surfaces
  • this increases infiltration and reduces Overland flow
  • this increases lag time as there is slow transportation of water to river channels due to interception
  • Peak discharge is lower as it takes water longer to reach river
  • for example, York took days for the water to flow into the river channel

Water And Carbon Cycle (8 decks)

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