HEC-GEORAS on a small
stream in North Branch,
Clear Creek
Zhihao Wang
Sep 2011

HEC-RAS
◦ perform one-dimensional steady and unsteady
flow river hydraulics calculations

HEC-GeoRAS
◦ pre- and/or post-process GIS data and HECRAS results for flood inundation mapping using
ArcGIS

HEC-GeoRAS creates a file of geometric
data for import into HEC-RAS, and
enables viewing of exported results from
RAS.
Preprocess
Postprocess

HEC-GeoRAS requires a DTM (digital
terrain model) in the form of TIN or GRID.
TIN of part of the North branch,
Clear Creek
30mDEM
8mDEM, 23m z
tolerance
8mDEM, 1m z
tolerance
Flow rate
generated by
GeoWEPP
(referred to as
runoff)

Create RAS layers:
◦ Stream centerlines, Banks, Flow paths, Cross
section cutlines, other optional layers
◦ By creating empty layers and digitize manually
Banks
Stream
centerlines
Flow paths

Cross section cutlines

Assign attributes to:
◦ Stream centerlines (names, topology, length)
◦ Flow paths (left/right/center)
◦ Cross section cutlines (river/reach name, bank
stations, elevation…)

Manning’s value
Extract GIS data
HEC-RAS
geometric data

Cross section view in HEC-RAS

Set up the flow rate data

2-year scenario simulation results
Conventional
tillage
No tillage
Conservation
tillage