If your plot does not look like this:- go to options on the Cross section data window Lets look at the profile for our model, click on the cross section data menu tab, then plot/profile g file? Name and save it in the Ras project directory you are using. Now is a good time to save your geometry data, remember the. The cross section interpolation tool has placed the cross sections at intervals ofĠ.096 m (evenly spaced), notice there is no slope on the profile
Your main geometry menu should now look like this Sections and enter the distances between each section. If you continued to have different cross sectional geometry at each cross-section, you would continue to add new cross. Now its time to interpolate cross sectionsIn the main geometry menu click on tools/XS interpolation and selectĮnter 0.1 m as the max distance between XSs, then hit the interpolate button and your geometry is complete Remember to change thedescription to reflect theupstream cross-section Remember toclick apply dataafter you haveentered the geometry The LOB, Channel & ROB distancesbetween sections need to be answeredsince the sections are parallel, then all three distance are the same (1.82m) (Since we have the same geometry we are going to make use of thecopy section function)Įnter the station chainage at the upstream end of the flume(for the flume the upstream end will be located at1.82m)Otherwise, if the geometry was different, you wouldClick options / add a new cross section Since the geometry is uniform from the upstream to downstream extent, we can make use of the cross section interpolation tool to compute the geometry with the specified cross section spacingĪdd a new cross section at the upstream end river station 1.82 m You also have to enter the locations where a flood plain would start if there was one, for this model we will assume the top of the flume is where the flood plain would start (hence at LOB=0m, ROB=0.0757m).Ĭlick on Apply Data to add the cross-sectionto the model and to view the sectionįlume Example Note the differentMannings nvalues in the channeland on the right andleft flood plains for a river. If there were floodplains, this boxdefines the horizontalright and left limitsof the chainagesof the main channel(see page after next for example)Įnter desired description of the cross section Mannings n valuesLOB & ROB would be the left and right flood plains respectively Entered from left to right looking down stream (HEC RAS ESTABLISHES THE DOWN STREAM END AS ZERO FOR A STARTING DISTANCE AN PROGRESSIVELY WORKS UPĮnter and apply data assuming an arbitrary datum of 100.00 m, notice the downstream reach length is zero since we are at the furthest downstream extent of the model Cross-sectional data Width- 7.57 cm (0.0757 m) Wall height- 12 cm( 0.12 m) Flume Length- 182 cm (1.82 m) Slope-none, horizontal Roughness- Plexiglass (n~0.0085) Discharge- 1.5 l/s ( 0.0015 m3/s) Cross section spacing 10 cm (0.1 m) Downstream boundary condition (critical depth at Junctions define where two reaches are connected Bridges and culverts Inline weirs/gates Off channel storage Pumping stations All can be modeled with a reasonable amount of Velocity head changes between cross sections Ineffective flow areas are can store but not convey water downstream Obstruction areas block flow completely Levee elevations confine flow to channel until the levees are overtopped
Geometry Cross sections define the channel/flume geometry Cross sections are defined by Station(x) and elevation (y) in the plane of theĬross section perpendicular to the flow River station, downstream reach length and cross section thalweg elevationĭefine the channel slope Overbank stations differentiate channel and floodplain characteristics Resistance to flow is defined by Manning n coefficients for both the channelĪnd floodplain Expansion and contraction coefficients define energy losses associated with againĬreate a reach- single or dendriticClick here Plan data(what combination of flow/geometry toĪfter you have entered the above, click O.K. Geometry (XS, bridges, weirs, etc.) (.g file)3.
Open project creates (.prj file) Includes:1. Surface elevation for a given discharge, geometry, and resistance Hydraulic Engineering Center:River Analysis Systemġ-D step backwater model Utilizes energy equation to compute water A Tutorial(Model Development of a Small Flume)