2014 AWRA Annual Water Resources Conference November 5, 2014 Tysons Corner, VA

Transcription

1 2014 AWRA Annual Water Resources Conference November 5, 2014 Tysons Corner, VA

2 HEC-RAS Overview, History, & Future How HEC-RAS Works Model Development Standard FEMA Assumptions Building A Model FEMA Levels of Study Model Results & Outputs Leveraging FEMA HEC-RAS Models Ways to leverage How to acquire FEMA Models

3 HEC-RAS is the most frequently used and widely accepted model for developing FEMA flood profiles and mapping. There are hundreds of thousands of models that have been developed to support FEMA Flood Insurance Studies throughout the United States. Flood studies don t just generate models, but also produce valuable supporting data: Terrain (LiDAR & Contours) Survey Field investigation data Models and supporting data are available to the public.

4 HEC-RAS is a River Analysis System modeling software, developed by U.S. Army Corps of Engineers, Hydrologic Engineering Center HEC-RAS What can we do with the software? Perform One-Dimensional Hydraulic Models Steady & Unsteady Flow Analysis Sediment Transport Analysis Water Quality Analysis Hydraulic Design and much, much more

5 Cross sections are the basic building blocks of HEC-RAS hydraulic modeling. Bridges Floodplains Culverts Dams

6 OldGen (HEC-2) NexGen (HEC-RAS)

7 HEC-RAS 5.0 will offer combined 1D and 2D modeling, including the ability to model hydraulic structures inside of 2D flow areas.

8 One-dimensional Hydraulic Model (1-D) A mathematical model that computes hydraulic conditions of flow for a constant discharge and only calculates the hydraulics in terms of flow depth variations and velocity in the direction of the stream line. Flow Path

9 HEC-RAS basic methodology is to compare energy between cross sections to determine the water surface elevation of the next section. This is referred to as a direct step method calculation. Basic Equations are: Energy Equation Continuity Equation V2 A2 V1 A1 Z: elevation of the bottom of the channel Y: elevation of the water surface V: flow velocity : coefficient g: gravity h e : head losses A: area of cross section Z V 2 g V 2 g Y2 2 Z1 Y1 1 he

10 HEC-RAS Basic Assumptions: 1. Cross sections have one water surface elevation (WSE) along the entire length. 2. Average water velocity and depth is adequate to determine WSE. 3. Water only flows perpendicular to the cross section. 4. Flow Q is constant in any given set of calculations.

11 2 basic model inputs Hydrology - Flows Floodplain Geometry & Characteristics Cross Sections Stream Line Structures HEC-RAS Model

12 Two main sources of flows are: Regression Hydrology Rainfall-Runoff Modeling

13 Where does the information come from to build geometry? Base Terrain Data Landuse & Imagery

14 Where does the information come from to build these models? Survey & As-builts Field Visits

15 FEMA Standard Assumptions: 1. Subcritical flow 2. Steady state flow 3. Profiles are smooth and ever rising (no drawdowns) 4. Volume is not considered

16 FEMA study methods Study Method Detailed Methods Limited Detail Studies Methods Approximate Methods Redelineated (Detailed) Products (Results) Floodplains, BFEs, & Floodway Floodplain & BFEs Floodplain Updated Floodplains, Unchanged BFEs & Floodway Base Terrain High-quality LiDAR or survey High-quality LiDAR or survey Typically DEM Newer and original Terrain Channel Geometry Surveyed Channels No survey for channels No survey for channels Existing Model Structure Geometry Surveyed Structures Limited structure survey No surveyed structures Existing Model Flow Data Regression or Rainfall-runoff Regression or Rainfall-runoff Regression Existing Flow Data Model Availability Definitely Yes If you re lucky Often HEC-2

17 HEC-RAS has over 20 standard output results table

18 Outputs can be visualized in plan or profile views

19 Water Surface Profiles can be converted to mapping products Profiles are combined with a terrain model (DEM or TIN) to delineate Special Flood Hazard Areas. Floodplains Depth Grids Velocity Grids Elevation (BFE) Grids Etc

20 Model can be used out of the box for: Sediment transport and scour modeling Water quality modeling (temperature, dissolved nitrogen, dissolved oxygen, etc.) Structure design Model components can be incorporated as: Base data for SWMM hydraulics Base data for a Flo-2D analysis Other useful model data: Terrain, LiDAR, & Contours Survey, Cross sections, & Structures Discharges (Flows) Gage Analysis HMS Models for rainfall-runoff modeling

21 FEMA Library All models and data (if available) Fee to research and collect data /fhm/st_order.shtm Map Service Center Maps and Mapping Products Effective DFIRMs GIS Layers for cross sections, floodplains, depth grids, etc.

22 First places to look: Local community floodplain administrator State or County Agency (Emergency Management, Department of Environment & Resources) Local CTP (Cooperating Technical Partner/State) -technical-partners-ctpprogram/cooperating-technicalpartners-ctp-program

23 Data is becoming more readily available. Download Models for: NC & NC Flood Risk Information System - Harris Flood Control District - WV Flood Tool -

24 Joseph C. Kirby, P.E., CFM Technical Director, Water Resources & GIS ESP Associates, P. A Kingdom Way Suite 208 Raleigh, NC