GIS in Water Resources

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GIS in Water Resources

• Review for Midterm Exam

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Data Models

• A geographic data model is a structure for
  organizing geospatial data so that it can be
  easily stored and retrieved.

Geographic coordinates
Tabular attributes
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Raster and Vector Data
Raster data are described by a cell grid, one
value per cell
Vector
Raster
Point
Line
Zone of cells
Polygon
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ArcGIS Geodatabase
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Geodatabase and Feature Dataset

• A geodatabase is a relational database that
  stores geographic information.
• A feature dataset is a collection of feature
  classes that share the same spatial reference
  frame.

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Feature Class

• A feature class is a collection of geographic
  objects in tabular format that have the same
  behavior and the same attributes.

Feature Class Object class spatial coordinates
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Object Class

• An object class is a collection of objects in
  tabular format that have the same behavior and
  the same attributes.

An object class is a table that has a unique
identifier (ObjectID) for each record
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Relationship
Relationship between spatial and non-spatial
objects
Water quality data (non-spatial)
Measurement station (spatial)
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National Hydro Data Programs
National Elevation Dataset (NED)
National Hydrography Dataset (NHD)
Watershed Boundary Dataset
NED-Hydrology
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1250,000 Scale Soil Information
http//www.ftw.nrcs.usda.gov/stat_data.html
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National Land Cover Dataset
http//landcover.usgs.gov/nationallandcover.html
http//seamless.usgs.gov/
Get the data
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National Water Information System
Web access to USGS water resources data in real
time
http//waterdata.usgs.gov/usa/nwis/
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Arc Hydro Components
GIS provides for synthesis of geospatial data
with different formats
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Burning In the Streams
Synthesis of Raster and Vector data
? Take a mapped stream network and a DEM ? Make a
grid of the streams ? Raise the off-stream DEM
cells by an arbitrary elevation increment ?
Produces "burned in" DEM streams mapped streams


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AGREE Elevation Grid Modification Methodology
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Geodesy, Map Projections and Coordinate Systems

• Geodesy - the shape of the earth and definition
  of earth datums
• Map Projection - the transformation of a curved
  earth to a flat map
• Coordinate systems - (x,y) coordinate systems for
  map data

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Latitude and Longitude in North America
Austin (30N, 98W) Logan (42N, 112W)
60 N
30 N
60 W
120 W
90 W
0 N
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Length on Meridians and Parallels
(Lat, Long) (f, l)
Length on a Meridian AB Re Df (same for all
latitudes)
R
Dl
D
R
30 N
C
B
Re
Df
0 N
Re
Length on a Parallel CD R Dl Re Dl Cos
f (varies with latitude)
A
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• Example What is the length of a 1º increment
  along
• on a meridian and on a parallel at 30N, 90W?
• Radius of the earth 6370 km.
• Solution
• A 1º angle has first to be converted to radians
• p radians 180 º, so 1º p/180 3.1416/180
  0.0175 radians
• For the meridian, DL Re Df 6370 0.0175
  111 km
• For the parallel, DL Re Dl Cos f
• 6370 0.0175
  Cos 30
• 96.5 km
• Parallels converge as poles are approached

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Horizontal Earth Datums

• An earth datum is defined by an ellipse and an
  axis of rotation
• NAD27 (North American Datum of 1927) uses the
  Clarke (1866) ellipsoid on a non geocentric axis
  of rotation
• NAD83 (NAD,1983) uses the GRS80 ellipsoid on a
  geocentric axis of rotation
• WGS84 (World Geodetic System of 1984) uses GRS80,
  almost the same as NAD83

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Vertical Earth Datums

• A vertical datum defines elevation, z
• NGVD29 (National Geodetic Vertical Datum of 1929)
• NAVD88 (North American Vertical Datum of 1988)
• takes into account a map of gravity anomalies
  between the ellipsoid and the geoid

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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)
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Universal Transverse Mercator

• Uses the Transverse Mercator projection
• Each zone has a Central Meridian (lo), zones are
  6 wide, and go from pole to pole
• 60 zones cover the earth from East to West
• Reference Latitude (fo), is the equator
• (Xshift, Yshift) (xo,yo) (500000, 0) in the
  Northern Hemisphere, units are meters

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UTM Zone 14
-99
-102
-96
6
Origin
Equator
-120
-90
-60
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ArcInfo 8 Reference Frames

• Defined for a feature dataset in ArcCatalog
• Coordinate System
• Projected
• Geographic
• X/Y Domain
• Z Domain
• M Domain

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X/Y Domain
(Max X, Max Y)
Long integer max value of 231 2,147,483,645
(Min X, Min Y)
Maximum resolution of a point Map Units /
Precision e.g. map units meters, precision
1000, then maximum resolution 1 meter/1000 1
mm on the ground
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Four Points
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One degree box and its four lines
Geographic Coordinates
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One Degree Box in USGS Albers Projection
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USGS Albers Projection
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Area Calculation in USGS Albers
81.09 km
111.79 km
111.79 km
Area 9130.6 km2
82.26 km
82.26 81.09
x 111.79 9130.5 km2
2
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North American Albers Projection
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Area Calculation in North American Albers
76.64 km
118.17 km
118.17 km
Area 9130.6 km2
77.89 km
77.89 76.64
X 118.17 9130.4
2
Take home message Lengths of lines change but
area is constant in Albers
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Two fundamental ways of representing geography
are discrete objects and fields.
The discrete object view represents the real
world as objects with well defined boundaries in
empty space.
Points
Lines
Polygons
The field view represents the real world as a
finite number of variables, each one defined at
each possible position.
Continuous surface
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Vector and Raster Representation of Spatial Fields
Vector
Raster
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Numerical representation of a spatial surface
(field)
Grid
TIN
Contour and flowline
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Grid Datasets

• Cellular-based data structure composed of square
  cells of equal size arranged in rows and columns.
• The grid cell size and extent (number of rows and
  columns), as well as the value at each cell have
  to be stored as part of the grid definition.

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Raster Sampling
from Michael F. Goodchild. (1997) Rasters, NCGIA
Core Curriculum in GIScience, http//www.ncgia.ucs
b.edu/giscc/units/u055/u055.html, posted October
23, 1997
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The scale triplet
Support
From Blöschl, G., (1996), Scale and Scaling in
Hydrology, Habilitationsschrift, Weiner
Mitteilungen Wasser Abwasser Gewasser, Wien, 346
p.
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Raster Generalization
Central point rule
Largest share rule
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Raster calculation some subtleties
Resampling or interpolation (and reprojection) of
inputs to target extent, cell size, and
projection within region defined by analysis mask


Analysis mask
Analysis cell size
Analysis extent
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Interpolation

• Estimate values between known values.
• A set of spatial analyst functions that predict
  values for a surface from a limited number of
  sample points creating a continuous raster.

Apparent improvement in resolution may not be
justified
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Topographic Slope

• Defined or represented by one of the following
• Surface derivative ?z
• Vector with x and y components
• Vector with magnitude (slope) and direction
  (aspect)

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Hydrologic Slope - Direction of Steepest Descent
30
30
67
56
49
52
48
37
58
55
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Slope
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Eight Direction Pour Point Model
Water flows in the direction of steepest descent
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Filling in the Pits

• DEM creation results in artificial pits in the
  landscape
• A pit is a set of one or more cells which has no
  downstream cells around it
• Unless these pits are filled they become sinks
  and isolate portions of the watershed
• Pit filling is first thing done with a DEM

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Flow Direction Grid
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Cell to Cell Grid Network Through the Landscape
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Contributing Area Grid
Drainage area threshold gt 5 Cells
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Delineation of Streams and Watersheds on a DEM
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Watershed and Drainage Paths Delineated from 30m
DEM
Automated method is more consistent than hand
delineation
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Stream Segments in a Cell Network
5
5
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Subwatersheds for Stream Segments
Same Cell Value
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Vectorized Streams Linked Using Grid Code to Cell
Equivalents
Vector Streams
Grid Streams
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Delineated Catchments and Stream Networks

• For every stream segment, there is a
  corresponding catchment
• Catchments are a tessellation of the landscape
  through a set of physical rules

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Raster Zones and Vector Polygons
One to one connection
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Area goes to Line Connectivity
For each catchment there is a unique drainage line
GridID is same on both Catchment and Drainage Line
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Watershed

• A watershed is the area draining to any point on
  the stream network
• A new kind of connectivity Area flows to a point
  on a line

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Connecting Drainage Areas to the Network
Area goes to point on line
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HydroID a unique identifier of all Arc Hydro
features
HydroIDs of Drainage Points
HydroIDs of Catchments
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Area flows to point on line connectivity through
GridID
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Area flows to point on lineconnectivity through
GridID
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DrainageLine Feature Class Inter-connectivity
using HydroID and NextDownID
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Catchment Feature Class Inter-connectivity using
HydroID and NextDownID
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Hydrologic processes are different on hillslopes
and in channels. It is important to recognize
this and account for this in models.
Drainage area can be concentrated or dispersed
(specific catchment area) representing
concentrated or dispersed flow.
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Drainage Density Dd L/A
EPA Reach Files
100 grid cell threshold
1000 grid cell threshold
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Network Definition

• A network is a set of edges and junctions that
  are topologically connected to each other.

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Edges and Junctions

• Simple feature classes points and lines
• Network feature classes junctions and edges
• Edges can be
• Simple one attribute record for a single edge
• Complex one attribute record for several edges
  in a linear sequence
• A single edge cannot be branched

No!!
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Polylines and Edges
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Junctions

• Junctions exist at all points where edges join
• If necessary they are added during network
  building (generic junctions)
• Junctions can be placed on the interior of an
  edge e.g. stream gage
• Any number of point feature classes can be built
  into junctions on a single network

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Connectivity Table
p. 132 of Modeling our World
J125
Junction
Adjacent Junction and Edge
E2
J124
E3
E1
J123
J126
This is the Logical Network
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Flow to a sink
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Network Tracing on the Guadalupe Basin
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Linear Referencing
Where are we on a line?
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Addressing