Automated Techniques for Hydraulic Modeling Applications David Knipe Engineering Section Manager

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

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

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

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

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)

Manning’s equation

Manning’s equation

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

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

Line directionality

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

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

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

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

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

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)”

Manning’s N

Channel Bank Stations Defines channel from left & right overbank

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 http://pubs.usgs.gov/sir/2013/5078

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

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

Automated Techniques for Hydraulic Modeling Applications David Knipe Engineering Section Manager