GIS Hydro 2006 Part 1
An Introduction to GIS and
Surface Hydrology
David Maidment
Steve Kopp
Nawajish Noman
Dean Djokic
Louis Wasson
1
UC 2006 Tech Session
Outline
• Hydrology overview
• GIS tools and data for hydrology – the building blocks
• GIS data models and specialized tools (ArcHydro)
• 10:15 Break
• A user’s perspective on ArcHydro
• Hydrologic modeling
• Hydraulic modeling
2
UC 2006 Tech Session
Water Resources Overview
• 2 broad categories of terrestrial water
– Surface water
– Groundwater
• 2 broad categories of water modeling
– Quantity
– Quality
• Today’s focus surface water quantity
3
UC 2006 Tech Session
Surface Water Quantity
• How much water is there?
– Rainfall-runoff modeling, a type of hydrologic modeling, determines
for a given storm on a landscape, how much water will become
runoff.
• Where will it go?
– Hydraulic modeling takes the quantity of water and the shape of
the landscape and stream channel and determines how deep the
water will be and what area it will cover in the event of a flood.
4
UC 2006 Tech Session
Hydrologic Modeling
• Goal: Find stream discharge, Q, at a location for a given
precipitation.
• GIS is used to summarize terrain and hydrologic
characteristics of the watershed for input to a model.
• Many ways to calculate Q.
– Statistical methods
• USGS regression equations (NFF, StreamStats)
– “Physical” modeling (rainfall-runoff models)
• HEC-HMS (successor to HEC-1), etc.
5
UC 2006 Tech Session
Hydrologic Modeling
• Map natural processes onto software tasks
• Aggregate landscape characteristics to simplify
– “Lumped parameter model”
6
UC 2006 Tech Session
Hydraulic Modeling
• Goal: to predict water surface elevations for the creation
of flood inundation maps.
– Also predict velocity, sedimentation, quality
• Input: channel and floodplain geometry with hydraulic
characteristics, plus discharge and initial water surface
level.
• Output: water surface elevation at each cross section and
other characteristics.
7
UC 2006 Tech Session
GIS Data for Hydrologic and
Hydraulic Modeling
• Digital Elevation Model
• http://seamless.usgs.gov/
• http://edna.usgs.gov/
• Watershed boundaries
• http://www.ncgc.nrcs.usda.gov/products/datasets/watershed/
• Hydrography
• http://nhd.usgs.gov/
• Soils
• http://www.ncgc.nrcs.usda.gov/products/datasets/statsgo/
• http://soildatamart.nrcs.usda.gov/
• Landcover
• http://seamless.usgs.gov/
• Current and historic water records
• http://waterdata.usgs.gov/nwis
• http://www.epa.gov/STORET/index.html
• Climate, weather, rainfall
• http://www.ncdc.noaa.gov/oa/ncdc.html
• http://www.nws.noaa.gov/ndfd/
• Channel geometry (cross sections)
8
UC 2006 Tech Session
Elevation Data
• Types
– DEM : Digital Elevation Model
– DSM : Digital Surface Model
• Data Structure
– Raster
– TIN
9
UC 2006 Tech Session
Where do you get DEM data?
• Sources
– USGS DEM, NED, DTED, ETOPO30, SRTM
– Interpolated from points and lines
– Generated photogrammetrically
– LiDAR
• Created with interpolation tools
– especially TOPOGRID, TopoToRaster
• What cellsize and accuracy?
– Horizontal and Vertical resolution must be appropriate for the
landscape and scale being modeled.
10
UC 2006 Tech Session
DEM Construction
• DEM construction issues
– Resolution and extent
– Projection (for hydrology - equal area)
– Source elevation data
– Interpolation techniques (IDW, spline, via TIN)
• Problems with contour input
– Specialized DEM construction software/components
(ANUDEM, TOPOGRID, TopoToRaster)
11
UC 2006 Tech Session
Drainage System
Watershed
(Basin, Catchment,
Contributing area)
Watershed Boundaries
(Drainage Divides)
Pour Points
(Outlets)
12
UC 2006 Tech Session
GIS Tools for Describing
Surface Water Movement
DEM
Apply Threshold
FLOW ACCUMULATION
FLOW DIRECTION
SINK
No
Are there any sinks?
Yes
FILL
Depressionless
DEM
STREAM ORDER
STREAM LINE
STREAM LINK
FLOWLENGTH
SNAP POUR
WATERSHED
13
UC 2006 Tech Session
Flow Direction
78 72 69 71 58 49
2
2
2
4
4
8
74 67 56 49 46 50
2
2
2
4
4
8
69 53 44 37 38 48
1
1
2
4
8
4
128 128 1
2
4
8
64 58 55 22 31 24
68 61 47 21 16 19
2
2
1
4
4
4
74 53 34 12 11 12
1
1
1
1
4
16
Flow Direction
Elevation
32
64 128
16
8
1
4
2
Direction Coding
14
UC 2006 Tech Session
Flow Accumulation
32
0
0
0
0
0
0
1
1
2
2
0
0
3
7
5
4
0
0
0
0
20
0
1
0
0
0
1
24
0
0
2
4
7
35
2
64 128
16
8
0
1
4
2
Direction Coding
15
UC 2006 Tech Session
Function Processing
DEM
Apply Threshold
FLOW ACCUMULATION
FLOW DIRECTION
SINK
No
Are there any sinks?
Yes
FILL
Depressionless
DEM
STREAM ORDER
STREAM LINE
STREAM LINK
FLOWLENGTH
SNAP POUR
WATERSHED
16
UC 2006 Tech Session
Creating Vector Streams
Value = No Data
1
1
1
2
2
2
2
2
2
StreamToFeature
2
2
NET_GRID
RasterToFeature
17
UC 2006 Tech Session
Stream Link
• Assign a unique value to each stream
segment.
– Can be used as input to Watershed tool
18
UC 2006 Tech Session
Stream Ordering
1
1
1
1
1
2
2
2
2
2
3
Strahler
19
UC 2006 Tech Session
1
1
1
2
1
1
1
1
1
1
2
3
3
4
7
Shreve
Watershed
• Delineate the contributing area to a cell or
group of cells.
20
UC 2006 Tech Session
SnapPour
• Snap the “pour point” of a watershed to the cell of
highest flow accumulation within a neighborhood.
– Prevents accidental creation of tiny watersheds on channel
side slopes.
Snap
distance
Cell you
clicked on
21
UC 2006 Tech Session
The cell that will be selected
(cell with highest flow accumulation)
Flow Length
• Calculate the length of the upstream or
downstream flow path from each cell.
22
UC 2006 Tech Session
Using the tools in ModelBuilder
23
UC 2006 Tech Session
DEM Errors – Sinks and Spikes
• Sinks: when sinks are (or are not)
sinks – lakes, depressions, …
– Global fill
– Dealing with internal basins
– Selective fill
• Depth
• Area
24
UC 2006 Tech Session
FilledSink
sink
DEM Editing
• Streams: when streams are not where they
“should” be
–Flat areas – difficulty in determining the flow pattern
–Barriers (roads) diverting the flow paths
• How to “model” bridges and culverts in DEM
• How to model dams
–Imposing the flow pattern - to burn or not to burn
(beware of the scale issues and artifacts – Saunders,
2000)
• Simple burn
• AGREE
• OMNR
25
UC 2006 Tech Session
DEM Editing (cont.)
• Boundaries - when watershed boundaries are not
where they “should” be
–To fence or not to fence
–Ineffective flow areas
26
UC 2006 Tech Session
DEM Editing (cont.)
• Tools
–Global operators
•
•
•
•
•
Fill
Agree (burn/fence)
OMNR (when it becomes available)
SWFWMD
Custom – model builder
–Micromanagement
• DEM Editing tools
• Custom – model builder
27
UC 2006 Tech Session
Enhanced Flow Direction (OMNR – Kenny & Matthews)
• Main steps
– Standard flow directions (D8)
– A hybridized raster/vector
topological analysis to assign D8
flow directions to cells that intersect
the network.
– An iterative raster single cell dilation
and D8 assignment from within
water bodies to focus flow towards
the virtual segments.
– A merging of results from steps 1, 2
and 3 to produce a final “enhanced
flow direction grid”.
28
UC 2006 Tech Session
Summarizing Watershed Characteristics
(Zonal Statistics)
• A zone is all the areas/cells with the same
value.
• Calculate a statistic within the zones for each
cell in a raster.
• Input zones can be feature or raster.
• Output as a raster, summary table, or chart.
–Max flow length per watershed
–Average slope per watershed
–Average curve number per watershed
29
UC 2006 Tech Session
Zonal Overlay (cont.)
Slope
Mean Slope per Watershed
Watersheds
30
UC 2006 Tech Session
Where is this functionality?
• ArcInfo GRID Functions
• ArcView 3.x Spatial Analyst
– Avenue requests
– Sample extension
• ArcGIS Spatial Analyst 8.x
– HydrologyOp containing ArcObjects methods
– Sample Toolbar on ArcObjectOnline
– ArcHydro data model tools
• ArcGIS Spatial Analyst 9.x
– Tools in the Spatial Analyst Toolbox
31
UC 2006 Tech Session
Demonstration of Spatial Analyst
Hydrology Tools
32
UC 2006 Tech Session