PRACTICAL UNIT 1 exercise task

Transcription

1 Practical Unit PRACTICAL UNIT 1 exercise task Developing a hydraulic model with HEC RAS using schematic river geometry data In the course of practical unit 1 we prepare the input for the execution of a onedimensional hydrodynamic numerical simulation within a schematic river reach. Therefore, basic knowledge of the applied software is indispensable, whereas the main focus is given to the problem orientated processing and not to the specific features of this software product (in principle same structure in other 1D programs like e.g. MIKE 11, WASPI). basic knowledge of the software building up a schematic river reach Aims Starting a new project Entering and editing geometric data (cross sections) Assignment of roughness values Definition and assignment of flow data (discharges [profiles]) Definition of boundary conditions Visualization of the input (cross sections, longitudinal plot, plan view) Input Data Information about the geometry of the schematic river reach Roughness values for channel and floodplains (LOB and ROB [left and right overbank]) Steady state flow data (discharge)

2 Practical Unit PRACTICAL UNIT 1 approach 1. Starting the program and creation of a new project starting the program The program HEC RAS is available for free download under ras/hecras download.html Furthermore, this web page features a detailed manual as well as a collection of practical examples. The newest version is currently version 4.0. Before starting the program it is necessary to set the computer to US standards. These settings concern the interpretation of dots and commas as well as date specifications. Start Einstellungen Systemsteuerung Regions und Sprachoptionen set to Englisch (USA) Now we are ready to start the program. HEC RAS is composed of several moduls, that means a main menu allows access to various sub menus (geometry, steady and unsteady flow data, simulation, visualization). main menu: Geometry Editor Enter / Edit steady flow data View cross sections View Profiles View General Profile Plot View computed rating curves main menu Enter / Edit quasisteady flow data Enter / Edit unsteady flow data View 3D multiple cross section plot Stage and flow hydrographs Hydraulic property table plots View DSS data Summary of errors, warnings and notes View summary output Enter / Edit sediment boundary conditions Enter / Edit water temperature boundary conditions Perform hydraulic design simulations Perform a water quality simulation Perform a sediment transport simulation Perform an unsteady flow simulation Perform a steady flow simulation View detailed output

3 Practical Unit File: new/open/save/rename/delete project, import/export data Edit: geometric data, flow data, sediment data, water temperature Run: perform analysis View: visualization and data tables Options: default values, unit system Help: online help, users manual, application guide, Mannings n reference online Names of loaded data files (project, plan, geometry, flow data) Project description Creation of a new project: Filename and project folder can be specified in File New Project please choose the directory which is given by your workstation number (C#) creation of a new project Don t forget to check if the unit system is set to SI (Système International)!!!

4 Practical Unit Input of geometry data geometry input In the next step we enter the geometric data of a schematic river reach. Geometric data consists of connectivity information for the stream system (river system), crosssection data and hydraulic structure data (bridges, culverts, weirs, etc.). The schematic reach has a total length of 4000 m and features an average bed slope of 1.5. Distance between cross sections is 100 m. The trapezoidal cross sections are characterized by an approximately 32 m wide river bed with 1:2 inclined river banks. The input of geometry data is carried out in the geometry window, where we have to define a river reach first. entering a river reach The flow direction within the river reach is defined by the starting and the end point of the line (upstream to downstream). Note: The form of the line (straight or curved) does not influence the results of the calculation. River bends are taken into account by entering different values for Downstream Reach Length in the cross section window.

5 Practical Unit The cross sections shown in the figure above are entered in. entering cross sections Entering new cross sections under Options Add A New Cross Section We start with the last cross section downstream labeled with river station 0 (for real rivers it is common to enter the river kilometer or hektometer). Cross sections are ordered within a reach from the highest river station upstream to the lowest river station downstream. Cross Section Coordinates: Downstream Reach Length: input of positioning and height of the terrain points (from orographic left to right river bank; positioning may also be negative, but the sequence must be in strict ascending order) Distance to the next downstream crosssection between left overbank (LOB), channel and right overbank (ROB). The last cross section downstream features a downstream reach length of 0 m, the others are determined by a downstream reach length of 100 m for all three sections, which means, that a straight river section is defined.

6 Practical Unit Manning s n Values Input of roughness values for LOB, Channel and ROB Main Channel Bank Stations delineation between channels and LOB / ROB Cont/Exp. Coefficient Manning (s/m 1/3 ) Strickler (m 1/3 /s) LOB Channel ROB contraction and expansion coefficents (have to be changed e.g. at bridges or weirs) Pushing the button Apply Data refreshes the graphical output. Having entered the first cross sections, further cross sections can be easily created by copying the first one. We start with the first cross section upstream. Options Copy Current Cross Section River Station: 4000 The elevation of this cross section must be altered corresponding to the given slope (1.5 * 4000m = 6 m): Options Adjust Elevations +6 Downstream Reach Length is set to 4000 m for LOB, Channel und ROB. The following cross sections are generated by interpolation: Tools XS Interpolation Between 2 XS s Constant Distance = 100 m interpolation of cross sections Note: in case of generated cross section with irregular river stations (e.g instead of 100) this can be changed by: Options Rename River Station (leave the * because it marks interpolated cross sections and facilitates the deletion of these cross sections This data has to be saved File Save Geometry Data under the name Praktikum_1.

7 Practical Unit Possibilities to check the input is graphically given in the longitudinal plot and the 3Dplot: or

8 Practical Unit Input of steady state flow data Normally, the modeled discharges are related to certain discharges like a 100 years flood (HQ 100 ) or HQ 30. Such steady state flow data can be entered in input Geometrie Input of steady state data Based on the function Enter/Edit Number of Profiles the number of discharges can be edited. For our practical unit we select the following 4 discharges: 300 m 3 /s, 500 m 3 /s, 700 m 3 /s and 1200 m 3 /s. Note: in HEC RAS the term profile is used synonymously for discharge and not for cross section. Definition of boundary conditions boundary conditions As boundary condition in case that no information about the correlation of discharge and water surface (Known W.S., rating curve) exist, the critical depth or the normal depth have to be selected. For the practical unit the normal depth is suggested. This means that as initial conditions the energy slope is selected (steady state conditions = energy, water surface and bed slope are equal). The definition of boundary condition must be done for both, upstream and downstream. The input data are saved by File Save Flow Data As Name: Praktikum_1 After defining all necessary input data (geometric and steady state data) the whole project has to be saved.

9 Practical Unit Visualization of input data visualization As done before, the geometric input can be basically visualized as longitudinal profile and 3D plot. Cross sections as well as the assigned roughness values can be visualized under.