Elevation Surface

Generation for

HEC-RAS Modeling

Jason Gibbons

Anderson Perry Natural Resource Tech/GIS Tech

GEKELER SLOUGH

• Surface Water Management Plan (SWMP)

Project Overview

– Located in Grande Ronde Valley, Union County,

Oregon

– SWMP – Gekeler Slough

• City of La Grande

• Union County

– Focus of SWMP

• Evaluate possible improvements to address:

– Water quality issues

– Water quantity issues

PROJECT LOCATION

PROJECT LOCATION

PROJECT STATISTICS

• Study Area:

– Approximately 18,000 Acres

• Gekeler Slough and Associated Tributaries:

– ±11.8 miles

– 68 Channel Structures (e.g., culverts, bridges)

• Most efficient and cost-effective way to

perform analysis?

ANALYSIS SOLUTION

• USACE HEC-RAS Software and ArcGIS

Software

– LiDAR data to produce surface in ArcGIS

– Import surface elevation data into HEC-RAS

– Perform HEC-RAS analysis

– Export results to ArcGIS

• Perform analysis to produce visual reference

guides

PROCESS

Source: USACE HEC-GeoRAS GIS Tools for Support of HEC-RAS using ArcGIS User’s Manual. Version 4.3.93. Feb., 2011

SURFACE GENERATION

• Mosaicked LiDAR

DEMs, procured from

DOGAMI, to produce

new surface in ArcGIS

– Entailed geoprocessing

operations for projection

transformations and vertical

elevation conversion to

correspond to NGVD 29

elevations

DEM INPUTS

TRANSFORMATIONS

• DOGAMI LIDAR data for the study area were delivered in the following

geographic coordinate systems and units: – Oregon Geographic Information Council High Accuracy Reference Network (HARN) Projection:

Oregon Statewide Lambert Conformal Conic

– Horizontal Datum: North American Datum 1983 (NAD 83) HARN

– Vertical Datum: North American Vertical Datum of 1988 (NAVD 88)

– Units: International Feet

• One LiDAR dataset is the exception to this, which was delivered in the following

coordinate system and units: – Projection: UTM Zone 11

– Horizontal Datum: NAD 83 HARN

– Vertical Datum: NAVD 88

– Units: Meters

• The Project Raster Tool was used to project the LiDAR DEMs into: – Projection: Oregon State Plane North Lambert Conformal Conic

– Horizontal Datum: NAD 83

– Vertical Datum: NAVD 88

– Units: International Feet

SURFACE GENERATION: MODEL BUILDER

FINAL SURFACE - DEM

File size: 1.09 GB

FINAL SURFACE - TIN

File size: 393 MB

CONCLUSION • Integration of HEC-RAS and ArcGIS software packages provided the following

benefits for this project: – Efficient DEM production for large project area.

– Ability to analyze data in one program and convert that data to a usable format in another.

– Ability to convey specific information related to floodwater elevations and evaluating alternative improvements for the Gekeler

Slough.

– MAPS – Tools that enhanced communication and collaboration among project partners.