The hydrologic cycle

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The hydrologic cycle
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Paths of precipitation on land
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Paths of precipitation on land

• Direct channel precipitation
• Overland flow
• saturation overland flow
• Interflow (throughflow)
• Groundwater flow

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Paths of precipitation on land

• Direct channel precipitation
• direct interception of precipitation by streams
• much less than 5 and usually less than 1 of
  runoff --but it always occurs
• reflects the area of surface water as a
  proportion of basin area,
• important where there is a large area of wetlands
  or lakes or during floods
• Overland flow
• Runoff occurring as water moves down the slope
  surface
• High flow velocity (10-500 m/hour)
• field studies demonstrated that Hortonian
  overland flow is virtually non-existent in areas
  w/ dense vegetation and thick soils--more often
  saturation occurs from below
• saturation overland flow
• saturation from below
• During a storm, as the water table gets close to
  the surface, saturated material abovesaturation
  overland flow
• water is returned to the surface by exfiltration
  
• in hillslope hollows where groundwater flow lines
  converge
• at slope concavities (i.e., base of many slopes)
  with decreasing hydraulic gradient, flow
  decelerates and therefore the depth of subsurface
  flow increases
• in thin soils over an impermeable surface, e.g.,
  rock, frozen ground, heavy soil horizon

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Paths of precipitation on land

• Interflow (throughflow)
• lateral movement of soil water between the ground
  surface and less permeable layer (soil layers,
  perched water table)
• can account for a significant proportion of the
  runoff in humid regions
• in sloping landscapes, interflow may exfiltrate
  at the surface producing saturation overland flow
• macropore flow (rapid interflow) soil water
  passing quickly to a stream through root canals,
  animal tunnels or pipes produced by subsurface
  erosion
• Groundwater flow
• in the zone of saturation below a perched or
  regional water table
• days, weeks or even years may pass before water
  that seeps to the water table eventually reaches
  a stream

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HORTONIAN OVERLAND FLOW

• OVERLAND FLOWSwhere the rainfall intensity
  exceeds the infiltration capacity, results.

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saturation overland flow
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overland flow
Diffuse overland flow. Note the raindrop impacts.
(Photo http//www.freefoto.com)
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SATURATION OVERLAND FLOW

• occurs mainly at the base of slopes and in
  concavities
• These areas become saturated during prolonged
  rain (by the combination of infiltration,
  interflow (flow down slope within the soil) and
  groundwater flow
• once the soil is saturated its infiltration
  capacity is zero
• any additional rain will not infiltrate - it be
  will stored on the surface or become overland
  flow.

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Which paths will reach stream first?
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hydrographs
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Hydrographs 1996-1997 storm event
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Lag to peak Q with different runoff generation
modes
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Expansion of saturated area after 46 mm
rainstorm, Vermont
Dunne and Leopold, 1978
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Seasonal change in saturated area, NE Vermont
Dunne and Leopold, 1978
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Drainage basins

• As basin area increases, discharge increases and
  lag time increases

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Drainage basins

• As basin area increases, discharge increases and
  lag time increases
• Bigger basins have larger water storage capacity

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rapid mobilization of old water paradox

• In many small catchments, streamflow responds
  promptly to rainfall inputs,
• But fluctuations in passive tracers (such as
  water isotopes and, in sea-salt dominated
  catchments, chloride) are often strongly damped.
• This indicates that storm flow in these
  catchments is mostly old water
• how do these catchments store water for weeks or
  months, but then release it in minutes or hours
  in response to rainfall inputs?

Kirchner, J.A., 2003, A double paradox in
catchment hydrology and geochemistry, Hydrol.
Process. 17, 871874
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A double paradox in catchment hydrology and
geochemistry
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• Perhaps the kindest thing one can say about the
  current state of knowledge is that the mechanisms
  by which catchments store water for extended
  periods, but then release it promptly during
  storm events, are not well understood.

• HYDROLOGICAL PROCESSES
• INVITED COMMENTARY
• Hydrol. Process. 17, 871874 (2003)

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What changes rates of infiltration? What changes
proportion of water that runs off vs. soaks in?
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Effects of landuse on hydrograph shape
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Infiltration change with time during rainfall
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Soil crusting - surface sealing and runoff
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Drainage Basins

• Drainage basinwatershed
• Drainage dividewatershed (UK)

http//facweb.bhc.edu
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Drainage Basins

• Drainage basinwatershed
• Drainage dividewatershed (UK)
• An area on a map outlined by a divide is known as
  a drainage basin
• All of the water within this basin will drain
  down to a stream then flow out of the basin
• No size restrictions on basins - can be large or
  small

http//facweb.bhc.edu
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The drainage basins of the Mississippi River

• Drainage basin the area from which a river gets
  its water supply

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The Columbia River Drainage Basin

• 675,000 km2
• 219 major dams
• Discharge of sediment to the ocean has decreased
  by 2/3 since the late 1800s

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Snake River system
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Drainage Basins

• Drainage basinwatershed
• Drainage dividewatershed (UK)
• An area on a map outlined by a divide is known as
  a drainage basin
• All of the water within this basin will drain
  down to a stream then flow out of the basin
• No size restrictions on basins - can be large or
  small

http//facweb.bhc.edu
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Strahler stream ordering
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Shreve stream ordering
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Strahler stream ordering

• What are these systems dependant on?

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http//facweb.bhc.edu
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Strahler stream ordering

• What are thses systems dependant on?
• Dependant on scalewhat qualifies as a stream?

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Characteristics of drainage basin morphometry
drainage density

• Drainage density (total length of
  streams)/(basin area)
• What would increase drainage density?

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Characteristics of drainage basin morphometry
drainage density

• Drainage density (total length of
  streams)/(basin area)
• What would increase drainage density?
• i rainfall, i veg, h runoff h erosion h drainage
  density
• h relief h erosion, h drainage density
• h erodability of parent material, h drainage
  density

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Characteristics of drainage basin morphometry
basin relief and ruggedness

• Relief of basin difference in elevation (highest
  elevation-elevation of basin mouth)
• Ruggedness numberdrainage density total relief
• Ruggedness is a good flash flood predictor

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Basin hypsometry
of total elevation
0
100
of total area
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Basin hypsometry
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Basin hypsometry
of total elevation
0
100
of total area
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Basin hypsometry
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Basin hypsometry
of total elevation
0
100
of total area
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Hypsometry of the Earth
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http//www.ilstu.edu/jrcarter/LDEO
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The peaks on Earth's curve represent the MEAN
ELEVATION OF THE CONTINENTS (800 m) and the MEAN
ELEVATION OF THE OCEAN BASINS ( 4000 m deep).
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1. Basin morphometry and discharge

• What is the primary difference between these two
  basins? Express as an equation.
• Sketch the flood hydrographs for these two
  drainage basins. Assume the basins are the same
  size, and have received equal rainfall amounts.
• Sketch both curves on the same graph

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2. Basin morphometry and discharge

• What is ruggedness? Express as an equation.
  Which basin is more rugged?
• Which basin would have a flashier hydrograph?
  Why?

Max elevation 8,000 ft Min elevation 6,000 ft

• Max elevation 6,500 ft
• Min elevation 6,000 ft

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3. Influence of geology on basin morphometry

• What are possible geologic settings for these
  cartoon drainage basins?
• Explain how drainage pattern reflects landforms
  or bedrock types.

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4. Basin characteristics and hydrographs

• Sketch and label storm hydrographs for the
  following. Put both hydrographs in each pair on
  the same graph
• basin pre and post urbanization
• Storm track moving up the basin vs down the basin
• According to Costa, (chapter 5 pg. 155) what are
  some common characteristics of basins with
  flashy hydrographs?

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6. The water budget

• Draw a cartoon to illustrate the hydrologic
  budget on page 160 of your book. Explain the
  terms of the equation.
• What are sources of long-term storage in a basin?
  Where is water stored during floods?

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7. Geomorphic mystery!

• What has happened here?

Time 1
Time 2
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