watershed delineation

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					Watershed Delineation
       Delineating Watersheds
► Watershed   (Catchment, Drainage Basin):
   A topographically delineated area drained by a
    stream system, or, the total land above some
    point, on a river/stream that drains past that
    point.
   Can range from a fraction of an acre to
    thousands of square miles.
   Why is this unit of area important to us as land
    and water managers?
  Delineating Watersheds Cont’d
► The  watershed is a hydrologic unit of land used as
  a physical, biological, socioeconomic, and political
  unit for the management and planning of natural
  resources.
► Aids in describing and quantifying the variables
  that influence water quality:
     Topography
     Soils
     Vegetation
     Land use, et.
        Watershed Delineation
► Identifies the boundaries of our hydrologic
  unit / area of study.
  Identifying Watershed Boundaries

► Steps   to delineation
   Trace/outline outline the main stem of the
    stream that you want to examine
   Trace all perennial or influential tributaries
   Locate the lowest point/outlet of the main stem
    and work uphill
  Identifying Boundaries Cont’d
► Working uphill, Identify the ridges and hill
 tops that divide the water from flowing into
 separate watersheds

► When   in doubt, consider,
   Where will the rain drops go
          Map Reading hints
► Water flows downhill (perpendicular to
  contours)
► Ridges make “V” shapes pointed downhill
► Draws make “V” shapes uphill
                 Area / Size
► Important   to watershed features because
   Estimating total annual water yield
   Flood potential
   Hydro characteristics: drainage density, time of
    concentration, drainage shape, etc..
   Amount of ground that you must deal with
     Methods to Determine Size
► Planimeter
► GIS
          Data (USGS etc.)
► Historical
► Dot method using a grid
      GIS as a measuring tool
► Polygons   have an area column
       Aspect and Orientation
► Differentwatersheds have unique
 differences and aspect has an affect

   Watersheds with south facing slopes are dryer
    due to evapotransperation and vegetation.
         Aspect Calculation
► Direction
   Vector perpendicular to        7       7 7
    the plane of the slope
   Values 0-360 (degrees)         6       6 6
   Southern aspect is 180         5       5 5

                              Aspect Map
       Aspect and Orientation
             the General of the main stem
► Orientation-
 of the watershed
   Obtain total stream length
   Determine 10% from the top and 15 % from
    the bottom
   Connect these points and get the aspect of that
    line
       Watershed Orientation
► East/west orientation is likely to have slopes
 that are predominantly north/south
               Slope Calculation
                                  6 5 6
 Rise over run                   5 7 6               40
 Percent or angle
                                  4 3 4
 Steepest point


 If cells are 10 m^2 then…

 (7-3) / 10 = .4*100= 40% slope




                                          Slope map
                    Slope
► The  vertical difference between the upper
  and lower most points divided by the
  horizontal difference in the points.
► Why is slope important”
   Runoff, stream transport power, sediment type
    and load, aggrading or degrading.
   Calculate for the entire reach and individual
    sites.
               Stream Profile
► Graph that provides longitudinal profile of
 the stream.
   X-axis is stream mileage
   Y-Axis is elevation
► Stream   profiles help to stratify zones
   Alpine, foothills, basins
► Locatesample sites
► Zones of erosion etc.
               Profile Cont’d
► Using   a 1:24,000 or better map
   Record interval at contours

   Using a graphing program, create a line graph
    with elevation as the y-axis and stream miles as
    the x-axis
                      Sinuosity
► The repetition downstream of patterns of channel
  curves for a given length of stream. (channel
  length / valley length)
► Measure of:
   Bends
   Curves
   Meanders
► Sinuosity   is important for:
   Stream Classification
   Variation in erosion and sediment concentration
         Calculating Sinuosity
► GIS
             Profiles in the field
► Longitudinal
► Standard Map and Map Wheels
              Stream Order
► Characterizesthe drainage networks
► Broad reference for flow characteristics of a
  watershed
► Higher streams usually mean higher flow
  volume
      Calculating Stream Order

► Single tributaries are order 1 streams
► Two 1st order streams meeting = order 2
► Two 2nd order streams meeting = order 3
► 1st order meeting a 2nd order = order 2
            Watershed Shape
► Watershed   shape has an effect on flow
  characteristics
► Shape can be calculated by form factors and
  circulatory ratios
► Circular watersheds will concentrate water quickly
  and have a flashy discharge
► Long narrow watersheds tend to have steep
  slopes, high overland flow, high sediment yields,
  lower peak volumes over long periods of time.
Relief:
Slope           Parent
                Material:
                Soil
                Enhancement
                (3 layers)

Relief:
Relative
Elevation
                  Organisms:
                  Fractional
                  Vegetation


Relief:
Compound
Topographic
Index (acc.
on slopes
perp. drain   Climate/Relief:
direction)    Aspect

				
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posted:10/25/2012
language:English
pages:29