1. Automated Techniques for Hydraulic Modeling Applications
David Knipe
Engineering Section Manager

2. Presentation Outline Basics of Hydraulic Modeling
Using the new local resolution NHD data in modeling
Using DEM or TIN topography to derive cross section points
Deriving hydraulic modeling parameters
Post processing of hydraulic modeling

3. IDNR modeling efforts Zone A modeling First Order Approximations
Geo – Sub Divided Area Rating

4. Basics of Hydraulic Modeling
Compute flood elevations
Determine floodway
Determine impact of projects
Bridge / Culvert modeling

5. HEC-RAS USACE modeling program / Hydrologic Engineering Center
Industry standard
1-d hydraulic modeling

6. Manning’s equation Q – peak discharge (cfs)
N – manning’s n (roughness)
A – Area
R – Hydraulic Radius (Area / Wetted Perimeter)
S – Slope of energy grade line (approximate by stream slope)

7. Manning’s equation

8. Manning’s equation

9. Geometric Setup for HEC-RAS
Stream Centerlines
Cross Sections
Bridge / Culvert modeling

10. Local Res NHD Under development Stream centerlines at 1:2400 or better
Much more dense than 24K NHD

11. Line directionality

12. Stream centerline Need to extract centerline from the NHD
Directionality of line is important

13. Cross section stationing
Use Tokens and “Polyline” commands to compute stationing
CrossSections = [] for row in arcpy.da.SearchCursor(“S_XS.shp", CrossSections.append(row[0]) for x in CrossSections: pt1 = StreamCenterline.intersect(x, 1).centroid sta = int(StreamCenterline.measureOnLine(pt1))

14. DEM / TIN High quality DEM’s are important (30M DEM will not cut it)
May need to enhance with below water information
Will need 3D analyst to do most functions

15. Interpolate Shape Need (Station, Elevation) for RAS
Use “InterpolateShape_3d” to create 3D layer
Use Linear Referencing tools to create M – or use Polyline measurement tools

16. Cross Sections in RAS Extend sections farther than normal
500 point limit – need to filter
Can write “sdf” file to import into RAS

17. Manning’s N Relating Manning’s N To NLCD dataset
Table from “Web Based implementation of Fast Dam Break Flood Modeling Capabilities (Altinakar, et al) (2011)”

18. Manning’s N

19. Channel Bank Stations
Defines channel from left & right overbank

20. Channel Bank Stations
Robinson, B.A., 2013, Regional bankfull-channel dimensions of non-urban wadeable streams in Indiana: U.S. Geological Survey, Scientific Investigations Report 2013–5078, 33 p., available only at

21. Post processing Floodplain delineations Depth Grids
Depth grids are a Risk MAP non regulatory product, but are easy to produce.

22. Post processing Need to remove artifacts
Smooth out boundary using “Bend Simplfy”

23. Automated Techniques for Hydraulic Modeling Applications
David Knipe
Engineering Section Manager