River Regimes
Bostcastle Flood
Bangladesh Annual & Catastrophic Flood
Flood Defense Schemes 

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Hydrological Change

What is a drainage basin? 
What is a watershed?

What are Inputs?
What are Outputs?
What are Flows?
What are stores? 

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Hydrological Change

A drainage basin is an area of land from which a river receives water.
A watershed is the area of higher ground which separates basins

Additions of water
Losses of water
Movements of water
Storage of water 

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Hydrological Change: Inputs & Stores


What is precipitation? 

What is vegetation storage?

What is surface storage?

What is soil water storage? 

What is groundwater storage? 

What is channel storage?

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Hydrological Change: Inputs & Stores


" The input into a drainage basin" (Water can be deposited from the atmosphere in the form of rain, hail, snow, fog etc)  

"Water stored in or on plants"

"Water stored on the ground (Puddles/Lakes)"

"Water stored in the soil" 

"Water stored in bedrock" 

"Water stored in the river channel"

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Hydrological Change: Flows

What is Interception? 

What is Through fall? 

What is Stem Flow?

What is Surface runoff?

What is Infiltration? 

What is Through flow?

What is Percolation?

What is Ground flow? 

What is Channel flow?

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Hydrological Change: Flows

"Precipitation being trapped by plants" 

"Water dripping off leaves" 

"Water flowing down plant stems/ tree trunks" 

"Water flowing over the ground"

"Water soaking into the soil"

"Water flowing downhill through the soil" 

"Water soaking from soil, into bedrock below" 

"Water flowing downhill through bed rock"

"water flowing in the channel river"

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Hydrological Change: Outputs

What is evapouration? 

What is Transpiration? 

What is Evapotranspiration? 

What is River Runoff? 

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Hydrological Change: Outputs

"Physical loss of water from surfaces into the atmosphere"

"Biological loss of water from a plant into the atmosphere through stomata in the leaves" 

"Evaporation and transpiration" 

"The major output from drainage basins. Loss of water from the river into the sea" 

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River Regimes

What is Discharge? 
What is it measured in?

What is a river regimes?
How is it  measured?
How is it averaged out?  

River regimes are influenced by.....?

Rainy season =
Temperature =
Warmer Season =  

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River Regimes

"The rate of flow of water in a river - at a particular point and time" 
"Measured in CUMECS (M^3/sec) 

"Annual discharge pattern" 
"Measured month by month" 
"Averaged out over 20 years"  

"Influenced by Climate" 

Rainy season = Highest flow
Temperature = Evapotranspiration and/or snow melt
Warmer Season = Lower Flow or Higher flow (If snow melt)

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Factors influencing River Regimes

Geology - How does this affect a river's regime? 

A Spring Maximum might be a result of what?

Evaporation is greatest when?

Precipitation amounts are ..?.. In many areas which seasons give the most precipitation?  

What are some of the human factors influencing river regimes?

How can the position of the measuring station influence a river regime?  

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Factors influencing River Regimes

Where underlying rock is mainly impermeable (Boscastle) - this will give a varying regime. Where rock is permeable it will act as a reservoir - when full, there will be large amounts of surface run off.

Melting Snow 

In summer or during higher temperatures

Precipitation amounts are seasonal... Winter and Autumn usually give the highest rainfall (Northern Hemisphere)

Reservoirs or the abstraction of water may lead to changes

If tributaries meet you may get an increased discharge. It also relates to the size and shape of a basin. 

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What is a flood hydrograph? 

What is lag time? 

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A graph showing precipitation input from a storm and how the discharge changes over a short period of a time. 

Lag time is the time between the peak rainfall and peak discharge

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Boscastle Flood - Quick Facts

  • When did Boscastle flood? 
  • Where is Boscastle? 
  • What sort of flood was it? 
  • When did the rain start? 
  • How much rain fell over what period of time?  
  • When did the river banks burst? 
  • When was the visitor centre cut off? 
  • When did search and rescue begin? 
  • How many deaths? 
  • How many people rescued?
  • How many cars swept away?  
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Boscastle Flood - Quick Facts

  • August 2004
  • North Coast of Cornwall 
  • Flash Flood 
  • 12.00am 
  • 440 millitonnes (8 inches) in 8 hours
  • 3.35pm
  • 4.00pm
  • 4.35pm 
  • 0
  • 100
  • 115
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