Freshwater and Society

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Freshwater and Society

• Module 1, part B

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Watersheds
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Hydrological cycle of a watershed
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Watershed definition

• Watershed
• An area of land that drains water, sediment and
  dissolved materials to a common receiving body or
  outlet
• The term is not restricted to surface water
  runoff and includes interactions with subsurface
  water
• Watersheds vary from the largest river basins to
  just acres or less in size

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Organization of watersheds

• A divide represents the boundary of a watershed
• Larger watersheds can often be divided into
  smaller units called subbasins, drainage areas,
  or water resource inventory areas

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Watersheds
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Watershed components

• Latitude, albedo climate
• Geology
• Topography
• Land Use
• Vegetation and impervious surfaces

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Watershed components Latitude

• Energy input into a watershed depends on solar
  height and length of daylight hours
• Determined by the latitude and season
• May 21, Seattle, WA solar altitude at noon is
  62.500
• January 21, Seattle solar altitude at noon is
  22.500

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Watershed components Albedo
Albedo is the reflectance of a surface. The higher the reflectance the less energy input into a watershed. Albedo is the reflectance of a surface. The higher the reflectance the less energy input into a watershed.
Surface Cover Albedo ()
Water 5-10
Bare soil (light colored, dry) 20-35
Marsh and Bogs 15-20
Forest (dense spruce) 5-10
Forest (hardwoods in leaf) 15-20
Snow (fresh) 80-95
Snow (old) 40-70
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Watershed components Climate
http//www.eia.doe.gov/emeu/recs/origin/climzone.g
if

• Temperature regime
• Relative humidity
• Precipitation patterns

http//www.epa.gov/ceisweb1/ceishome/atlas/nationa
latlas/climatezones.htm
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Watershed components Climate

• Precipitation
• Temperature
• Relative humidity (RH)
• Wind

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Watersheds Average annual precipitation

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Watersheds Potential evapotranspiration

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Watersheds Water surplus or deficit

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Watershed components Geology

• Bedrock
• Type and distribution of soils

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Geology Soil permeability

• The ease with which water penetrate or pass
  through a bulk mass of soil or a layer of soil

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Geology soil pore space and water content

• Total porosity of a soil determines maximum water
  content at saturation soils within zone of
  aeration are seldom saturated.
• Textural (primary) porosity voids between
  aggregates.
• Structural (secondary) porosity voids
• within aggregates fracture or poor
• zones

http//wrgis.wr.usgs.gov/open-file/of99-168/Pp-lim
estone.jpg
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Geology Groundwater vs. soil moisture

• Groundwater
• Subsurface water in the zone of saturation that
  is free to move under the influence of gravity,
  often horizontally to stream channels
• Soil Moisture
• Subsurface water in the unsaturated zone held in
  place by capillary forces or osmotic pressure

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Geology moisture content of various soils

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Geology Infiltration

• Infiltration is the flow of water downward
  through the upper layers of soil

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Geology infiltration capacity during a storm

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Geology soil moisture profile after a rain event

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Geology seasonal infiltration trends

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Geology seasonal variation in watershed runoff

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Geology Saturation and runoff generation
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Watershed components Topography

• Topography
• Slope
• Aspect

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Watershed components Topographic interactions
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Watershed components Land use and vegetation

• Vegetation
• Slows runoff
• Reduces soil compaction
• Prevents soil erosion
• Reduces pace of raindrop splash
• Reduce soil material moving downslope
• Influences timing of snowmelt runoff
• Influences water yield

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Land use Stormwater discharge vs. land use
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Land uses Effects upon hydrology/water quality

• Natural Events
• Fires
• Wind storms
• Disease outbreaks
• Floods
• Volcanoes
• Climate change

• Land Uses
• Flood control
• Timber production
• Urban development
• Hydroelectric
• Agriculture
• Mining

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Watershed components land Use

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Organization of a watershed
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Watershed Water budgets

• Water budget
• Evaluation of sources of supply vs. discharges
  with respect to a drainage basin

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Watershed Water budgets

• Annual water budget for Lawrence Lake, Michigan,
  and Mirror Lake, New Hampshire

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Watershed Water budgets

• Water budgets provide a graphic depiction of the
  distribution of moisture throughout the year in
  any given area
• An idealized budget, however, is rarely achieved
• Examples from Los Angles, CA and Pullman, WA,
  illustrate the range of potential deviation from
  the ideal water budget

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Watershed water budget Pacific Northwest
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Watershed Aquatic ecoregions

• North America has been divided into eight major
  aquatic ecoregions
• Arctic rivers and lakes
• Large temperate lakes
• Temperate headwaters and lakes
• Large temperate rivers
• Endorheic rivers, lakes, and springs
• Xeric-region rivers, lakes, and springs
• Temperate coastal rivers and lakes
• Subtropical coastal rivers and lakes

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Aquatic Ecoregions of North America
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Watershed components