AUTOMATING MANNING S N COEFFICIENT VALUE ASSIGNMENTS FOR HYDRAULIC MODELING

Transcription

1 Imagery Source: Bing Maps via ESRI AUTOMATING MANNING S N COEFFICIENT VALUE ASSIGNMENTS FOR HYDRAULIC MODELING Kyle Gallagher, GISP Black & Veatch Special Projects Corp.

2 Project Overview USACE Tulsa District 2,200 river miles 17 reservoirs Steady and Unsteady flows Prepped with HEC-GeoRAS Simulated with HEC-RAS Sources: ESRI, USGS NHD

3 Hydraulic Modeling General Overview Simulating the flow of water downstream based on a provided elevation source(s) and calibrated to historic flooding events HEC-GeoRAS extension used to prepare hydraulic modeling components in a geodatabase Stream centerlines are digitized from aerial imagery Cross sections (XS) lines are digitized perpendicular to a stream s flow direction Elevations are assigned to the XS lines and areas in between XS are interpolated Flood boundaries produced in HEC-RAS Lots of equations!

4 Manning s n Coefficient Values Component of the hydraulic modeling process Used to account for surface friction (roughness) as water moves downstream Assigned to each cross sections left and right overbanks Based on Land Cover each category has its own respective n value

5 The Problem Extract N Values tool in HEC-GeoRAS Extremely long cross sections create many elevation and N- value change points that tend to exceed HEC-RAS limitation of 500 points per cross section.

6 The Problem Needed to find a workaround solution to assign one weighted n value to each left and right overbank section Distance away from stream centerline How much of a XS s controlling area falls within each specific landcover category? Used ModelBuilder for testing exported to a Python script with input parameters for automation Source: mapzlibrarian.blogspot.com

7 Initial Data Setup Digitize Stream Centerline and XS XS Bounding Polygon Split XS Bounding Polygon with Centerline to create Left and Right Polygons ET GeoWizards Populated L_R field as either L or R R L Stream Centerline XS XS Bounding Polygon XS L/R Polygons

8 Input Script Parameters All I/O data for an individual stream stored in its own feature dataset Output Cell Size = 30m Mask = XS Bounding Polygon

9 Polygon to Raster Land Cover polygon feature class based on Manning s n field Produces ManningsN Raster NoData Open Water areas removed (NoData) Used to mask subsequent rasters

10 Euclidean Distance Stream Centerline Euclidean Distance Raster

11 Map Algebra #1 (1/ Euclidean Distance Raster) * Produces Inverse Distance Weighted (IDW) Raster Represents weighted component

12 Map Algebra #2 IDW * ManningsN Produces IDW x N raster Incorporates Manning s n values

13 Resulting Raster Outputs Raster outputs are used to perform a weighted average calculation Weighted Avg = Sum (IDW x N) / Sum (IDW)

14 Euclidean Allocation Converted XS lines to a raster using HydroID field (XS Raster) Used XS Raster for EA input Each XS Area of Influence (AOI) is defined

15 Raster to Polygon XS Allocation Raster XS AOI Will contain GRIDCODE field with HydroID values

16 Intersect L/R polygons with XS AOI polygons XS-AOI-LR intersect L R

17 XS-AOI-LR polygons Add Field: CODE_LR Calculate Field: CODE_LR = [GRIDCODE] & [L_R]

18 Zonal Statistics As Table Two runs XS-AOI-LR & IDW Raster XS AOI LR & IDW x N Raster CODE_LR field IDWxN SUM / IDW SUM = Manning s n value (after Join) CODE_LR and SUM fields are most relevant

19 Add Fields Will not be able to perform SUM / SUM when tables are joined Add N field to IDWxN Zonal Stats table will represent final n value Add SUM2 field to IDW Zonal Stats table Calculate SUM2 = SUM

20 Join Field (Data Management) Use the CODE_LR field of each Zonal Stats table Carry over the SUM2 field Calculate N = SUM / SUM2 Manning s n values can now be attached to the HEC-GeoRAS cross sections

21 Summary Needed to find workaround solution to assign Manning s n values to cross sections 4,500 cross sections 9,000 Manning s n values generated Batch processing allowed for multiple streams to be calculated at once Time and money saver, allowed project to move forward

22 Questions?? Kyle Gallagher, GISP