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GIS4048/5100 Applications in GIS. GIS in Hydrology. Watershed management Definitions Algorithms Watershed delineation Automatically delineating watersheds Flow length Raster to vector conversion. Overview. Watershed management Definitions Algorithms & Watershed delineation

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gis in hydrology

GIS4048/5100 Applications in GIS

GIS in Hydrology
  • Watershed management
  • Definitions
  • Algorithms
  • Watershed delineation
  • Automatically delineating watersheds
  • Flow length
  • Raster to vector conversion
overview
Overview
  • Watershed management
  • Definitions
  • Algorithms & Watershed delineation
  • Automatically delineating watersheds
  • Flow length
  • Raster to vector conversion
watershed management
Watershed management
  • Important topic in modern landscape management
  • In the past, landscapes have been managed by ownership
  • Plant & animal species do not obey ownership boundaries
  • Need for physically or biologically based land divisions
watershed management1
Watershed management
  • Watersheds are physically & biologically meaningful
  • Various interest groups can agree on watershed boundaries
  • Watersheds are easily defined based on elevation models
  • Management activities applied on watershed-by-watershed basis
overview1
Overview
  • Watershed management
  • Definitions
  • Algorithms & Watershed delineation
  • Automatically delineating watersheds
  • Flow length
  • Raster to vector conversion
definition of watershed
Definition of watershed
  • “The region draining into a river, river system, or body of water”
    • American Heritage Dictionary
  • The upstream area of any given point on the landscape
  • Physically defined by drainage point and upstream area
  • Also known as basin, sub-basin, catchment, and contributing area
definition of watershed1
Definition of watershed
  • A watershed can be defined at a broad regional scale, such as the Columbia River watershed

or . . .

definition of watershed2
Definition of watershed
  • At a small local scale, such as the Husky Stadium watershed
overview2
Overview
  • Watershed management
  • Definitions
  • Algorithms & Watershed delineation
  • Automatically delineating watersheds
  • Flow length
  • Raster to vector conversion
how it works algorithm
How it works: algorithm
  • Axiom: Water always flows downhill
  • For any point on a grid representing a landscape,a drop of water can be traced downhill

 direction of flow is known for every DEM cell

  • For any point on a grid representing a landscape,a flow pathway can be traced back uphill

 flow accumulation is known for every DEM cell

  • Uphill back-tracing proceeds to a ridgeline or to the edge of the grid
  • Termination of uphill back-tracing defines watershed boundary
watershed delineation steps
Watershed delineation: Steps

ArcToolbox:

  • Create a depressionless DEM
  • Calculate flow direction
  • Calculate flow accumulation
  • Create watershed Pour points
  • Delineate watersheds
watershed delineation creating a depressionless dem

elevation

Watershed delineation: Creating a depressionless DEM
  • DEM must eventually drain off edge of grid
  • Areas of internal drainage will result in unprocessed areas
  • FILL routine fills in sinks or cuts off peaks creating a new grid with no drainage errors
watershed delineation flow direction
Watershed delineation: Flow direction
  • Every cell flows into another cell or off the grid edge
  • Flow direction is calculated as the direction of steepest downward descent
  • Flow direction is stored in numerically-coded schema
  • Flow direction values are not ratio or proportional
  • Flow direction is calculated for each cell, resulting in a new grid theme
watershed delineation flow direction2

north-flowing cells

  • coded as 64
Watershed delineation: Flow direction
  • This is a bookkeeping scheme, not a ratio or proportion
watershed delineation flow direction3
Watershed delineation: Flow direction
  • Individual cells/zones in the grid are coded for flow direction
watershed delineation flow accumulation
Watershed delineation: Flow accumulation
  • Each has just been coded for direction of flow
  • Cumulative flow is calculated from flow direction
  • Output grid is created where values are the number of tributary (upstream) cells
  • Lower accumulation values are ridge tops
  • Higher accumulation values are valleys & stream channels
watershed delineation flow accumulation1
Watershed delineation: Flow accumulation
  • Higher-flow cells have a larger value

3

5

1

watershed delineation watershed pour points
Watershed delineation: Watershed “Pour points”
  • Watersheds are defined by outlets (pour points)
  • Pour points should be placed in high-flow pathways
  • Basins will be generated from pour point to ridgeline or to upstream sub-basin
  • Pour points should be numerically coded per sub-basin
  • Pour points should be converted to a grid layer
watershed delineation delineating watersheds
Watershed delineation: Delineating watersheds
  • Preliminary steps are completed
    • Filled DEM
    • Flow direction
    • Flow accumulation
    • Pour points created & converted to grid
  • Run tool to create watersheds
overview3
Overview
  • Watershed management
  • Definitions
  • Algorithms & Watershed delineation
  • Automatically delineating watersheds
  • Flow length
  • Raster to vector conversion
watershed delineation automatic delineation
Watershed delineation: Automatic delineation
  • Basin tool
  • No user control
  • Pour points automatically selected by “intersection” of highest-flow pathways and grid edge
overview4
Overview
  • Watershed management
  • Definitions
  • Algorithms & Watershed delineation
  • Automatically delineating watersheds
  • Flow length
  • Raster to vector conversion
flow length
Flow length
  • Flow distance for every cell to outlet
flow length1
Flow length
  • Flow distance for every cell to closest stream
raster to vector conversion
Raster to vector conversion
  • Conversion from rasters to lines or polygons
    • Stream network as line shape
    • Stream links as points
    • Stream order (Strahler or Shreve)
    • Watershed grid theme as a polygon theme
applications of watershed analysis
Applications of watershed analysis
  • Watershed themes can be incorporated with other raster & vector analysis methods
    • Road & stream densities
    • Forest age analysis
    • Sedimentation effects
    • Habitat area in different basins
    • Animal movement analysis