Hydrological Modeling in Gis
Hydrological Modeling in Gis
Hydrological Modeling in Gis
Overview
Core GIS tools for surface water analysis DEM data and processing
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Demo
Not enough (droughts) Too much (floods) Of wrong kind (water quality) In a wrong place (spatial distribution) At the wrong time (temporal distribution)
Hydrologic modeling (precipitation-runoff modeling), determines for a given storm on a landscape, how much water will become runoff.
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.
Hydrologic Modeling
Goal: Find stream discharge, Q, at a location for a given precipitation event. There are many ways to calculate Q.
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Statistical methods
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GIS is used to summarize terrain and hydrologic characteristics of the watershed for input to a model.
Hydrologic Modeling
Map natural processes onto software tasks. Aggregate landscape characteristics and define the layout.
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Hydraulic Modeling
Input: Channel and floodplain geometry with hydraulic characteristics, plus discharge Q and initial water surface level. Output: Water surface elevation at each cross section and other characteristics. GIS is used to summarize terrain and hydraulic characteristics of the channel for input to a model and post process hydraulic modeling results (surface determination).
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Watershed boundaries
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Hydrography Soils
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Drainage System
Watershed
(Basin, Catchment, Contributing area)
Watershed Boundaries
(Drainage Divides)
Pour Points
(Outlets)
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DEM
FLOW ACCUMULATION FLOW DIRECTION
Apply Threshold
SINK
No
Depressionless DEM
FILL
Flow Direction
78 72 69 71 58 49 74 67 56 49 46 50 69 53 44 37 38 48 64 58 55 22 31 24 68 61 47 21 16 19 74 53 34 12 11 12 2 2 1 2 2 1 2 2 2 4 4 4 2 4 1 4 4 8 4 4 4 8 8 4 8 4 16
128 128 1
2 1
2 1
1 1
Elevation
32 16 8 4 64 128 1 2
Flow Direction
Direction Coding
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Flow Accumulation
0 0 0 0 0 0 0 1 3 0 0 2 0 1 7 0 0 4 0 2 5 0 2 4 0 0 0 1
20 0 1 7
24 0 35 2
32 16 8
64 128 1 4 2
Direction Coding
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Value = No Data
1 2
1 1 2 2 2 2 2 2
StreamToFeature
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NET_GRID
RasterToFeature
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Stream Link
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Watershed
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Use the Zonal Statistics tool. 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.
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Max. flow length per watershed Average slope per watershed Average curve number per watershed
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Watersheds
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Elevation Data
Types
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DEM: Digital Elevation Model (bare Earth) DSM: Digital Surface Model (with buildings and trees)
Data Structure
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Sources
Existing data: USGS DEM, NED, DTED, ETOPO30, SRTM - LiDAR, IfSAR - Generated photogrammetrically - Interpolated from points and lines
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Horizontal and Vertical resolution must be appropriate for the landscape and scale being modeled.
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Resolution and extent Projection (for hydrology use equal area) Source elevation data Interpolation techniques
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For hydrologic applications, use TopoToRaster. Avoids problems with contour input - Creates hydrologically correct DEM
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Sinks: when sinks are (or are not) sinks lakes, depressions,
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DEM Editing
Flat areas Difficulty in determining the flow pattern Barriers (roads) diverting the flow paths
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Imposing the flow pattern - to burn or not to burn (beware of the scale issues and artifacts Saunders, 2000.)
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Burning streams Fencing boundaries Bowling lakes Flow splits Selective filling of sinks Streams draining into sinks
Deranged terrains
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Combined dendritic/deranged
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Start
Burning streams
DEM grid
Legend
Start
Bowling lakes
River feature class
DEM grid
Stream segmentation
Fill sinks
Grid datasset
Legend
Alternative Processing
DEM grid
DEM Reconditioning
Grid datasset
Fill sinks
Fencing
Legend
Start
Alternative Processing
Function
DEM grid
HydroDEM (1) grid
HydroDEM (2) grid
Grid datasset
Flow direction
Catchment grid
Alternative Processing
Fill sinks
Fill sinks (2)
Legend
Feature class dataset
Alternative Processing
Build walls
Grid datasset
Flow direction
Function
DEM Reconditioning
Flow direction
Flow accumulation
Optional Function
Flow direction
Function
Optional Function
Stream definition
Stream grid
End
Arc Hydro
Tools in the Arc Hydro Toolbox - Arc Hydro Toolbar
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Arc Hydro
Arc Hydro
Extension of geodatabase model for support of water resources applications (template data model) Culmination of a three-year process (19992002) led by D. R. Maidment through GIS in Water Resources Consortium (Arc Hydro book) Collection of tools for support of Arc Hydro geodatabase design and basic water resources functions Starting point for water resources database and application development
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Target audience: Water resources (surface) community interested in quick start in ArcGIS implementati Starting point for project model design Not a do all design Not implementation/application specific, but provides the key components to develop on top of
The user needs to add additional data structures for their specific requirements theres still work to be done!
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Flow
HydroID
Time
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Detailed representation at the end of corresponding chapters in the book (e.g., p. 51)
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A set of freely available ArcMap-based tools that are a companion to the Arc Hydro data model Developed and maintained by ESRI Water Resources Team (not a core product or a sample) Hundred (100) + tools organized in one main and several supporting toolbars in ArcMap - Geoprocessing (toolbox) implementation of many of the existing tools. All new tools are developed in gp environment.
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Exercise Arc Hydro data model (manage key identifiersHydroID, JunctionID, Next DownID, etc.) Provide some functionality common to water resources analyses
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Terrain analysis Watershed delineation and characterization Tracing and accumulation through networks Schema (node-link) development Specialized data I/O (XML, Excel, etc.)
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Customizable
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Economy of development - Why reinvent the wheel? - Established configuration methodology - Established development framework Industry standard - Established techniques rolled into a publicly available utility Training and support Free maintenance ESRIs commitment to the water resources community
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Demo
Database design Data preparation Terrain preparation Watershed delineation Watershed characterization Parameterization Model pre- and postprocessing
Semigeneric Generic
Model Specific
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Topics Overview
Stream statistics Hydrologic modeling (HEC-HMS, GeoHMS) Hydraulic modeling (HEC-RAS, GeoRAS) H&H integration considerations
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Regression Equations
Used to estimate streamflow statistics, both high and low flows, for ungaged sites (in uncontrolled flow environment) Relate streamflow statistics to measured basin characteristics Developed by all 48 USGS districts on a state-bystate basis through the cooperative program (usually sponsored by DOT) Often not used because of large efforts needed to determine basin characteristics Users often measure basin characteristics inaccurately.
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Q100 = 0.471A0.715E0.827SH0.472
Where A E SH
is drainage area, in square miles is mean basin elevation, in feet is a shape factor, dimensionless
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Role of GIS
Speed up the process (instead of hours, minutes). Provide a common (single) access to the methodology (for users and maintenance). Systematize methodology and datasets used in the process (repeatability). Provide better tools for deriving characteristics for regression equation determination. Provide a map-based user interface. Web and desktop implementation are based on Arc Hydro.
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USGS lead effort State-based ArcGIS Server technology Hosted in Denver Extended functionality
Source: http://water.usgs.gov/osw/streamstats/ssonline.html
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Results - Web
Watershed delineation
20-30 seconds, not much difference with respect to size of the watershed
Parameter computations
10s 1 minute, depends on the region (what parameters to get) and somewhat on the size
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HEC-GeoHMS
HEC-HMS: Hydrologic Engineering Center Hydrologic Modeling System: allows calculation of precipitation runoff processes. HEC-GeoHMS:
ArcGIS preprocessor for HMS - Transforms the drainage paths and watershed boundaries based on DEM into a hydrologic data structure that can be used to model the watershed response to precipitation
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HEC-GeoRAS
HEC-RAS: Hydrologic Engineering Center River Analysis System: allows performing one-dimensional open channel steady and unsteady flow calculations. HEC-GeoRAS:
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Prepare geometric data for import into HEC-RAS Processes simulation results exported from HEC-RAS
Integration Approach
Mix of planning, GIS, and H&H modeling operations (not a push-button operation)
Types of integration
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(e.g., land use/soils/CN or rainfall processing Arc Hydro or general GIS data processing
Linked
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GeoHMS GeoRAS
Integrated
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DSS
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Key steps
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E.g., location of HMS modeling elements and RAS cross sections - Identify sources of precipitation input into the hydrologic model and techniques for their incorporation into the dataset. E.g., Nexrad rainfall - Develop the GeoHMS model (and precipitation submodel).
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Finalize and run the HMS model and generate results (DSS). Develop the GeoRAS model. Finalize and run RAS, taking HMS results as input. Feedback between HMS and RAS is manual.
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Integration Planning
Identify where outputs from one model (HMS) become input to the second one (RAS).
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Place hydrologic elements (subbasins, reaches, junctions) to capture flows at points of interest (confluences, structures). Place hydraulic elements (cross sections) at points of interest. Identify/Specify element-naming conventions between the two models (persistent or transient names).
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Precipitation Sources
Identify sources of precipitation input into the hydrologic model and techniques for their incorporation into the dataset.
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Follow all principles in development of a hydrologic model. In addition, take into consideration integration planning aspects developed earlier.
Placement of flow exchange points - Naming conventions
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Develop Arc Hydro time series for the final subbasin delineation and export to DSS.
Export to HMS.
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Meteorological Component
Develop a custom gauge for each subbasin or for each rainfall observation element with corresponding weights for subbasins. Export the time series for the subbasin gauge from Arc Hydro time series data structure into DSS.
Arc Hydro
DSS
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Complete HMS model with any additional parameters including meteorological model and control specifications. Follow all principles in HMS model development (calibration, etc.).
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DSS View
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Follow all principles in development of a hydraulic model for element placement (confluences, structures, ) In addition, take into consideration integration planning aspects developed earlier
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Naming conventions (add name of the HMS element to the cross-section that will get the elements flows)
Export to RAS
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Complete RAS model with any additional parameters including initial and boundary conditions. Follow all principles in RAS model development (calibration, etc.).
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Construct the floodplain based on the results in the .sdf. Review the results with respect to spatial integrity (extents of cross sections, ineffective flow areas, disconnected flood areas, etc.). Clean results. Revisit RAS.
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GISHMSRAS Feedback
At present, it is manual and at the discretion of the modeler.
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Postprocessing (GeoRAS)
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Floodplain Discontinuity
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Cross-Section Interpolation
TIN-interpolated cross sections
RAS-assumed terrain
Terrain
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Questions?