1. Introduction to GIS David R. Maidment
Center for Research in Water Resources
University of Texas at Austin

2. Presentation Outline Using GIS to connect hydrology and meteorology
Representation of spatial objects in GIS
Terrain analysis using Digital Elevation Models
Geodesy and map projections

3. Hydrologic Cycle: Connecting the Land Surface with the Atmosphere

4. Connecting Hydrology and Meteorology
Two Spatial Scales
Drainage basin scale for consideration of severe storms and flood (Nexrad radar precipation as input, flood runoff as output)
Regional or global scale for consideration of climate change (Global climate models as input, time series of river flows as output)

5. Regional flood analysis in Houston
Study region

6. Nexrad Rainfall for Storm of Oct 1994

7. Discharge in Buffalo Bayou at Katy October, 1994 storm

8. Calibrated Flow with HEC-HMS

9. Global Runoff (mm/yr)
According to NCAR’s CCM3.2 Global Climate Model (GCM)

10. GTOPO30 - 30” Digital Elevation Model of the Earth
Source:

11. Drainage in North America
Source:

12. Drainage Basins of North America
Source:

13. Streamflow Hydrographs for Large Basins
Runoff Input from Climate Model
Streamflow Output at River Mouth
Amazon River
MacKenzie River
Yangtze River
Congo River

14. A Fundamental Dilemma Land Surface Hydrology has:
drainage patterns organized by rivers and watersheds which are spatially discrete
analysis in Cartesian coordinates (x,y,z)
Atmospheric Science has:
circulation patterns which are spatially continuous over the earth
analysis in Geographic coordinates (f, l, z)
GIS can be used to connect these two spatial frameworks

15. Presentation Outline Using GIS to connect hydrology and meteorology
Representation of spatial objects in GIS
Terrain analysis using Digital Elevation Models
Geodesy and map projections

16. Discrete and Continuous Space
Discrete Space: Vector GIS
Continuous Space: Raster GIS

17. Geospatial Database: a set of compatible data layers or themes

18. Spatial Data: Vector format
Vector data are defined spatially:
(x1,y1)
Point - a pair of x and y coordinates
vertex
Line - a sequence of points
Node
DRM
Polygon - a closed set of lines

19. Feature Attribute Table
Fields
Records

20. Relational Linkages Descriptive Attributes Spatial Attributes
Water Right
Locations
Descriptive Attributes

21. Locations on the Stream Network
Digital Stream Network
Connects Control Point Locations

22. Watersheds defined using a Digital Elevation Model

23. Spatial Data: Raster format
Cell size
Number of
rows
NODATA cell
(X,Y)
Number of Columns
Definition of a Grid in GIS

24. Points as Cells

25. Line as a Sequence of Cells

26. Polygon as a Zone of Cells

27. Raster-Vector Data Model
Real World

28. Presentation Outline Using GIS to connect hydrology and meteorology
Representation of spatial objects in GIS
Terrain analysis using Digital Elevation Models
Geodesy and map projections

29. Study Region in West Austin
Hog Pen Ck
4 km
4 km

30. Watershed Delineation by Hand Digitizing
Watershed divide
Drainage direction
Outlet

31. 30 Meter Mesh Standard for 1:24,000 Scale Maps

32. DEM Elevations
720
720
Contours
740
720
700
680
740
720
700
680

33. DEM Elevations
Contours
700
680

34. Eight Direction Pour Point Model32 16 8 64 4
128 1 2

35. Direction of Steepest Descent1 1 67 56 49 53 44 37 58 55 22 67 56 49 53 44 37 58 55 22
Slope:

36. Flow Direction Grid 2 4 8 1 16
128

37. Austin West 30 Meter DEM Elevations in meters ftp://ftp. tnris. state
Austin West 30 Meter DEM Elevations in meters ftp://ftp.tnris.state.tx.us/tnris/demA.html

38. Flow Direction Grid 32 16 8 64 4
128 1 2

39. Grid Network

40. Flow Accumulation Grid3 2 3 2 2 2 11 1 1 11 1 15 1 15 2 5 2 5 24 1 1 24
Link to Grid calculator

41. Flow Accumulation > 5 Cell Threshold3 2 11 1 15 24 5

42. Stream Network for 5 cell Threshold Drainage Area3 2 2 1 11 1 15 2 5 1 24

43. Streams with 200 cell Threshold (>18 hectares or 13
Streams with 200 cell Threshold (>18 hectares or 13.5 acres drainage area)

44. Watershed Outlet

45. Watershed Draining to This Outlet

46. Watershed and Drainage Paths Delineated from 30m DEM
Automated method is more consistent than hand delineation

47. DEM Data Sources 30m DEMs from 1:24,000 scale maps (urban watersheds)
3" (100m) DEMs from 1:250,000 scale maps (rural watersheds)
15" (500m) DEM for the US resampled from 3” DEM (large drainage basins)
30" (1km) DEM of the earth (GTOPO30)

48. Presentation Outline Using GIS to connect hydrology and meteorology
Representation of spatial objects in GIS
Terrain analysis using Digital Elevation Models
Geodesy and map projections

49. Shape of the Earth
It is actually a spheroid, slightly larger in radius at the equator than at the poles
We think of the
earth as a sphere

50. Geographic Coordinates (f, l, z)
Latitude (f) and Longitude (l) defined using an ellipsoid, an ellipse rotated about an axis
Elevation (z) defined using geoid, a surface of constant gravitational potential
Earth datums define standard values of the ellipsoid and geoid

51. Ellipse Z b O a X  F1  F2 P An ellipse is defined by:
Focal length = 
Distance (F1, P, F2) is
constant for all points
on ellipse
When  = 0, ellipse = circle Z b O a X F1   F2
For the earth:
Major axis, a = 6378 km
Minor axis, b = 6357 km
Flattening ratio, f = (a-b)/a
~ 1/300 P

52. Ellipsoid or Spheroid Rotate an ellipse around an axisZ b O a a Y X
Rotational axis

53. Representations of the Earth
Mean Sea Level is a surface of constant
gravitational potential called the Geoid
Earth surface
Ellipsoid
Sea surface
Geoid

54. Definition of Elevation
Elevation Z P
z = zp •
z = 0
Land Surface
Mean Sea level = Geoid
Elevation is measured from the Geoid

55. Coordinate System A planar coordinate system is defined by a pair
of orthogonal (x,y) axes drawn through an origin Y X
Origin
(xo,yo)
(fo,lo)

56. Earth to Globe to Map Map Projection: Map Scale: Scale Factor
Representative Fraction
Globe distance Earth distance =
Scale Factor
Map distance Globe distance =
(e.g. 1:24,000)
(e.g )

57. Conic Projections (Albers Equal Area, Lambert Conformal Conic)

58. Cylindrical Projections (Universal Transverse Mercator)
Oblique

59. Azimuthal (Lambert Azimuthal Equal Area)

60. Presentation Summary Using GIS to connect hydrology and meteorology
Representation of spatial objects in GIS
Terrain analysis using Digital Elevation Models
Geodesy and map projections