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

128

16

1

8

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 - Land Use

– Flow Path Centerlines (optional) - Levee Alignment

– Main Channel Banks (optional) - Ineffective Flow Areas

– Cross Section Cut Lines - Storage Areas

• Water surface profile data and velocity data exported from HEC-RAS simulations are processed by HEC-GeoRAS 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 one-

dimensional steady flow, unsteady flow, sediment transport/mobile bed computations, and water temperature modeling.