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GIS Applications in Watershed Analysis …..the watershed unit. Dr. Dennis L. Johnson Assistant Professor Michigan Technological University COMET Hydrometeorology 99-2 Friday, 25 June 1999. Today’s Purpose. Introduce the Concepts of a GIS Applications of a GIS Focus on the Watershed Unit

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gis applications in watershed analysis the watershed unit

GIS Applications in Watershed Analysis…..the watershed unit

Dr. Dennis L. Johnson

Assistant Professor

Michigan Technological University

COMET Hydrometeorology 99-2

Friday, 25 June 1999

today s purpose
Today’s Purpose
  • Introduce the Concepts of a GIS
  • Applications of a GIS
  • Focus on the Watershed Unit
  • …. Get you thinking …...

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what is a gis
What is a GIS ?
  • A GIS is a Geographical Information System
  • A series of data layers (maps) that represent some feature on the earth’s surface
  • Ability to “overlay” !!
    • All data is “georegistered”

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georegistered
Georegistered ?
  • Representing a curved surface in a flat plane
  • Locating that plane on the earth
  • 3 issues
    • sphere
    • datum
    • projection

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sphere datum
Sphere & Datum

Mathematically describe a sphere

Lock it down by making it touch the earth somewhere NAD27- Kansas

Use satellites in modern day

NAD83

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project to a flat surface
Project to a Flat Surface

Touches at the equator

Touches at 2 lines of latitude

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unwrap the cylinder
Unwrap the Cylinder

One cylinder for each data layer

Represent the data electronically

A GIS!!!

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gis layers
GIS Layers

Elevations

Discharge Points

Rivers

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a dem
A DEM
  • A Digital Elevation Model or DEM is used to represent the elevations of a section or area of land.
  • The DEM is generally a gridded or raster data set.
  • A raster data set means a series of rows and columns with each grid cell representing a property such as elevation.

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create a dem from a topographic map
Create A DEM from a Topographic Map

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other views
Other Views

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assign flow directions
Assign Flow Directions

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our simple area
Our Simple Area

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each cell flows into another
Each Cell Flows Into Another
  • Note that each grid cell flows into another grid cell and so forth.
  • One could tally or keep track of the total number of grid cells that flow into each “downstream” grid cell.
  • This is generally known as a flow accumulation data set.

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our flow accumulation
Our Flow Accumulation

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let s look at an example
Let’s Look at an Example

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add rivers
Add Rivers

Juniata College

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zoom in
Zoom In

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assign flow directions1
Assign Flow Directions

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calculate flow accumulations
Calculate Flow Accumulations

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overlay streams
Overlay Streams

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let s delineate a watershed
Let’s Delineate a Watershed

Just Below Raystown Lake (dam)

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delineate raystown lake
Delineate Raystown Lake

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another view
Another View

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isolate raystown lake
Isolate Raystown Lake

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south facing slopes
South Facing Slopes

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buffer the streams 100m
Buffer the Streams ~100m

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find south faces 100m from stream
Find South Faces < 100m from Stream

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slide32
DEM

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flow direction
Flow Direction

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slope
Slope

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stream delineation
Stream Delineation

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k values
K Values

K = 1.2

K = 0.48

K = 2.1

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velocity
Velocity

V = KS1/2

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flow length
Flow Length

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advantages of gis
Advantages of GIS
  • Time Savings
  • Replication -Precision not Accuracy!!!
  • Ancillary Data
  • Data Reuses

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lake superior swe
Lake Superior SWE
  • U.S. Army Corps of Engineers
  • Manage Lake Superior
  • Sault Ste. Marie Locks
  • Snowfall is major contributor

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