GIS tools for surface water
modeling and analysis
http://resources.arcgis.com/en/communities/hydro/
Digital Elevation Models
Elevation data in raster
format – GIS analysis
Digital Elevation Model (DEM)
DEM in Grid Ascii format
ncols
2218
nrows
2013
xllcorner 203315.48791178
yllcorner 905650.13397789
cellsize 8.8654680523268
NODATA_value -9999
5.27725 55.36783 55.52513 55.79526 …
57.22343 57.69468 58.06146 58.32586 …
…
Scale
Datums
• Define the shape
of the earth
– Ellipsoid (size and
shape)
– Origin and
Orientation
(aligns ellipsoid to
best fit for region
of work)
http://www.icsm.gov.au/mapping/datums1.html
Projections
Displaying
the earth on
2
dimensional
maps
The “World From Space”
Projection from ESRI,
centered at 72 West and 23
South. This approximates
the view of the earth from
the sun on the winter
solstice at noon in
Cambridge, MA
Map projections
• Spatial relationship between locations on
earth and their relative locations on a flat map
• Mathematical expression
• Cause distortion of one or more map
properties (scale, distance, direction, shape)
Map projection classifications based
on distortion characteristics
Conformal – maintains local shapes
and angular relationships
Ex: Mercator projection:
Equal-Area – maintains areas
Ex: Albers Equal-Area
Conic projection:
Equidistant – distance from a single
location to all other locations are
preserved
Azimuthal – maintains accurate
directions from a single location to
all other
Q: Why project data?
A: Accurate calculations with GIS software
Choosing projections
• Look at maps
• USA: State Plane
• World: Universal
Transverse Mercator
(UTM) - maintain area
when east-west width
< 6 degrees longitude.
UTM Zones
Numbered 1 through 60 from Longitude 180
UTM projection
• Conformal (area preserved within zones)
• Cylindrical surface
• Zones - 6 degrees of longitude wide
Data integrity matters
• Look at metadata for reported errors.
• Raster data needs sinks identified and filled
for hydrology analysis.
ArcGIS Tools
•
•
•
•
•
•
Projections
Fill Sinks
Flow Direction
Flow Accumulation
Stream Definition
Watershed Delineation
Flow Direction
• Finds drainage
networks and divides
• Direction determined
by elevation of
surrounding cells
(water flows into only
1 cell – the one with
the lowest elevation
surrounding each cell)
Eight Direction Flow Direction Model
32
64
16
8
128
1
4
2
Flow Accumulation
• Number of cells contributing to runoff into a
given cell
Finding watersheds
• Find all cells that flow
into a chosen source
cell.
Finding drainage networks
Geodatabases for data model
• Holds and manages collection of datasets
• Used to define spatial and tabular behavior
Topology relationships
Attribute relationships
Domains and subtypes
Networks
ArcHydro
• Describes geospatial and temporal data
• Addresses 3 questions:
– What are the water resource features of the landscape:
– How does water move through the system?
– What are the time patterns of water flow and water
quality?
HEC-GeoHMS
• Transforms drainage paths and watershed
boundaries into a hydrologic data structure
that represents the drainage network
• Allows users to:
–
–
–
–
visualize spatial information
document watershed characteristics
perform spatial analysis
delineate sub-basins and streams
HEC-GeoRAS
http://www.hec.usace.army.mil/software/hec-georas/
• Create line themes for input to HEC-RAS as RAS Themes
–
–
–
–
Stream Centerline
Flow Path Centerlines (optional)
Main Channel Banks (optional)
Cross Section Cut Lines
- Land Use
- Levee Alignment
- Ineffective Flow Areas
- Storage Areas
• Water surface profile data and velocity data exported
from HEC-RAS simulations are processed by HECGeoRAS for GIS analysis
–
–
–
–
floodplain mapping
flood damage computations
ecosystem restoration
flood warning response
Using GIS with US Army Corps of
Engineers Hydrologic Engineering
Center (HEC) Software
• HEC-GEOHMS
http://www.hec.usace.army.mil/software/hec-geohms/documentation/HEC-GeoHMS_Users_Manual_10.1.pdf
• HEC-GEORAS
http://www.hec.usace.army.mil/software/hec-georas/documentation/HEC-GeoRAS_43_Users_Manual.pdf
Hydrologic Modeling System (HEC-HMS)
http://www.hec.usace.army.mil/software/hec-hms/
• designed to simulate the precipitation-runoff processes of
dendritic watershed systems.
River Analysis System (HEC-RAS)
www.hec.usace.army.mil/software/hec-ras/
• performs onedimensional steady
flow, unsteady flow,
sediment
transport/mobile
bed computations,
and water
temperature
modeling.