Processing Geospatial Data with HEC-GeoRAS 3.1 CLICK Good afternoon class, I am Brad Endres and today I will present my project entitled Processing Geospatial Data with HEC-GeoRAS 3.1. You should be familiar with HEC-GeoRAS from Friday’s presentation by Lim, so I plan to highlight some of the finer points of using this extension. Brad Endres CVEN 689 28 April 2003

Overview Hydrologic Review Hydraulics Review Applicable Software Data Requirements Major Functions of GeoRAS Demonstration of Capabilities Application to Area of Interest Benefits and Drawbacks Questions Since we have a variety of engineers in class, I will start by giving you some background knowledge, or review, of hydrology and hydraulics. I will introduce the leading software packages that can be used in conjunction with ommercial GIS software – specifically ESRI’s ArcView program. I will cover the digital data that is required to effectively use these programs. A demonstration of GeoRAS using the example data provided by the Hydrologic Engineering Center will showcase the capabilities. An application to an water resources problem area will depict its analytical capabilities. I’ll give you my perspective on the benefits and drawbacks of using GeoRAS and I’ll entertain any questions you might have at the end of the briefing. CLICK

Hydrologic Review Engineering Hydrology Occurrence, circulation, & distribution of water Frequency & magnitude of events (flood/drought) for engineering designs Gage station Hyetograph Hydrograph Scientific and engineering hydrology are very broad topics, so I just want to cover the basics to help you understand how the software programs incorporate these principle in their modeling abilities. As engineers, our main objective in studying the waters of the earth is to find out how much we can expect to encounter in a certain area, and how often we expect to encounter it. We want to protect society from the extreme events of floods and droughts, so we make estimates using proven methods and equations that result in a flood frequency analysis. Some of the components involved include U.S. Geological Survey gaging stations,, hyetographs that depict rainfall intensity (in/hr or cm/hr) for the 3 major regions of the U.S., and the resulting hydrograph at a water shed outlet that shows discharge (cfs or cms) over time. CLICK

Hydraulics Review Hydraulics Results in design specifications for bridges, culverts, and hydraulic structures Water Surface profile calculations based on flow data Energy Equation Example Floodplain By closely approximating these hydrologic variables for a give watershed, engineers are able to design effective flood control structures or water supply facilities. Of particular importance in hydraulics is the calculation of the water surface profile of a stream for the purposes of floodplain management. Using the inputs from hydrologic studies of a watershed, the hydraulic engineering seeks to find out how high the water will rise for a given rainfall event. The first law of thermodynamics, known as the conservation of energy equation, allows for the computation of a water surface elevation. It basically states that the head energy at a point downstream equals the head energy upstream minus the head loss due to friction between the points. Manning’s equation applies to open channel flow and is used to calculate the discharge rate at a cross section of stream using an estimated value of roughness called Manning’s n. CLICK

Hydraulics Review Floodplain Delineation Conventional Method of quad maps & hand calculations Digital Method Digital Terrain Model (DTM) in ArcView 3.2 GeoRAS automates geometry calculations HEC-RAS models given flow & delineates floodplain Export back to ArcView for additional grids One result of applying the energy equation is the water surface elevation, or height above the channel bottom at each calculated cross section. When compared to the elevation of the surrounding terrain, a floodplain can be delineated to indicate the level to which the water will rise. The old method for doing this called for hand drawing cross sections on topographic, or quadrangle, maps, and recording the contour lines that were crossed. When plotted and connected, these points served as the cross section profile of the stream at a specific point. With GIS tools, this can now be done using software programs if the appropriate data is available. If a digital terrain model exists, then the GeoRAS extension to ArcView can be applied to automate the previously described channel geometry. This data can be imported to the Hydrologic Engineering Center’s River Analysis System to delineate the floodplain through computer simulation. Once exported back to ArcView, a floodplain can be delineated on the terrain model, as well as depth and velocity grids that provide further analytical capability to the engineer. CLICK

Applicable Software ArcGIS w/ extensions HEC-HMS HEC-RAS 3D & Spatial Analyst HEC-GeoHMS HEC-GeoRAS HEC-HMS Simulates rainfall-runoff for the watershed HEC-RAS Simulates water surface profile of a stream reach

Data Requirements Triangular Irregular Network (TIN) DEM (high resolution) use stds2dem.exe if downloading from USGS Land Use / Land Cover Manning’s Coefficient See USGS website CRWR image

Major Functions of GeoRAS Interface between ArcView and HEC-RAS What does it do? PreRAS Menu - prepares Geometry Data necessary for HEC-RAS modeling GeoRAS_Util Menu – creates a table of Manning’s n value from land use shapefile PostRAS Menu – reads RAS import file; delineates flood plain; creates Velocity and Depth TINs

Demonstration of Capabilities 3-D Scene Load TIN Create Contour Lines 3-D Scene

Demonstration of Capabilities Create Stream Centerline Create Banks Theme Create Flow Path Centerlines Create Cross Section Cut Lines Add/Create Land Use Theme Generate RAS Import File

Demonstration of Capabilities Land Use Theme Stream Centerline Right Bank Flow Path Centerlines Cross Section Cut Lines

Demonstration of Capabilities Generate RAS GIS import file Open HEC-RAS and import RAS GIS file Complete Geometry, Hydraulic, & Flow Data Run Analysis Generate RAS Export file

Demonstration of Capabilities RAS GIS import file:

Demonstration of Capabilities RAS GIS export file:

Demonstration of Capabilities New GIS data PostRAS features Water Surface TIN Floodplain Delineation – polygon & grid Velocity TIN Velocity Grid

Demonstration of Capabilities Floodplain Delineation (3-D Scene)

Demonstration of Capabilities Depth Grid (Darker = Deeper) Velocity Grid (Darker = Faster)

Application to Area of Interest Background on Bolinas Lagoon, CA USGS Map USACE Map

Application to Area of Interest Bolinas Lagoon, CA USACE Image USACE Image

Application to Area of Interest Employing ArcView, GeoRAS, and RAS for Main Channel Depth Analysis (1968) PreRAS PostRAS 13.5 ft

Application to Area of Interest Employing ArcView, GeoRAS, and RAS for Main Channel Depth Analysis (1988) PreRAS PostRAS 21.0 ft

Application to Area of Interest Analysis of Results Sensitivity to stream centerline placement Accuracy improves with more XS cut lines XS cut lines hard to draw on meandering stream Possible deepening of the main channel over time Analysis of area complicated by tidal flows Validate findings FEMA floodplain maps USACE studies Bolinas watershed

Benefits & Drawbacks Overall Benefits Elevation data is more accurate with TIN files Better representation of channel bottom Rapid preparation of geometry data (point and click) Precision of GIS data increases precision of geometry data Efficient data transport via import/export files Velocity grid Depth grid Bolinas Lagoon on 10m DEM

Benefits & Drawbacks Overall Benefits Floodplain maps can be made faster Floodplain maps can include several flow scenarios HEC-RAS allows steady & unsteady flow analysis GIS tools aide engineering analysis Automated calculation of functions (Energy Equation) Structural validation of hydraulic control features Voluminous data on World Wide Web Makes data into visual event – easier for your brain to process! More GIS!

Benefits & Drawbacks Overall Drawbacks Time required to learn several software packages Availability of TIN or high resolution data Estimation of Manning’s Coefficient Few LU/LC files have this as attribute data Creating XS cut lines demands attention to detail Velocity distribution data may not be calculated HEC-RAS export file without velocity data means no velocity TIN or grid

Questions What are your questions? New 3-D Viewer in HEC-RAS 3.1