Project 2

Objective:- To Develop a Hydraulic Model for a Major River selected from particular area using RAS Mapper tool of HEC-RAS. Calculating catchment area over a River reach of 10 Km and do flow calculations for the river using UH method. Considering Steady flow and Unsteady Flow analysis both and run the simulation model for different profiles.

Tools used:- High resolution DEM file, Toposheets, Google Earth Pro, MS excel, Flood estimation report by CWC, HEC-RAS, Autocad, 25 and 100 year isopluvial data etc.

• Launch the HEC-RAS and start a new project by clicking File->>>>New project. Give desired name and location and select OK button. Then, go to options menu and select units system from us customary to SI and press Ok button. a dialog box will appear asking to change. Press Yes. 

• Now, click on the RAS Mapper sign available on option bar to open RAS Mapper or go to GIS Tools->> RAS Mapper. After Mapper is opened, Go on to Tools option from menubar and set projection for project. After setting projection select New Terrain option from same Tools option from menu bar.

• A new terrain layer dialog box will appear. Click on + icon on upper left part of screen. File manager box to select the terrain file will appear.

• select the downloaded DEM file and click on Open button. Then after click on create button of Terrain dialog box. A dialog box asking permission to  set SRS will appear. Click on Yes.

• Creation of Terrain layer will be started. After few minutes DEM file will be imported and a Terrain layer will created on window.

Our imported DEM file will look like as shown below. We can change some properties by going to Terrain option on bottom left part of Mapper window and right clicking there. Select the image display properties and change the properties as you like. 

We can also add contours by selecting plot contours and setting their intervals, color etc.

Now we can see our river flow path in middle portion of our DEM file. For better understanding we can also add map layers to this file.

For this go onto Map layers option and right click there. Select the option Add web imagery layer. Now a dialog box will appear with different satellite and maps. Select Google Satellite and click on OK.

Now we will see map layer too where we can clearly see our river selected for project.

Thus now after identifying our river go on to Geometry data window and select File->>>> save geometry data as. Enter the desired name for geometry and click OK.

Now we need to draw our River reach, its flow path and bank lines. For this, follow the following steps:-

• Select the Geometries option from upper left part of Ras mapper window and on Ras geometry button. Right click on Rivers button and select edit geometry option. 

• Draw the reach of river and double click at last point. A box will appear asking name and reach of river. give the desired name and reach name and press OK.

• Now again right click and select close geometry. A dialog box will appear asking save edits. Click on Yes.

• Now similarly right click on bank lines option and click on edit geometry. Draw left and right bank lines by same way as reach line drawn above and double click at last. For better understandimg of bank lines we can draw it by selecting map layers on. Now after drawing both lines we can right click on bank lines option and select stop editing and press Ok on edit geometry dialog box.

• Now, similarly draw the flow paths by selecting flow path and repeating the steps as depicted above.

• Now select cross sections--> right click->> edit geometry. Start drawing by drawing a line for bank stations from left to right bank lines. after drawing again right click and select stop editing. Save the edits.

Thus now after following all these steps our river geometry is ready to use. Go on to file menu and select save button. Geometry file will be saved under selected project.

Now, go to Hec-RAS main window. Go edit>> geometric data and geometric data window will open. We can view cross sections data by going to cross section option.

we will enter manning's N values as cross sectional data is directly taken from gis, so it need to be eneterd.

Now, we need to calculate flow of the river using UH method. For this we will need raw data and parameters to draw a UH for a river flow. We need to download flood estimation report by CWC for any desired river basin as per our choice and use it. In this file we will find all data required fo our calculations and will use it as per our need as shown in steps below:

• First of all we need to find Equivalent Slope. For this we calculate catchment area and length of stream from origin to site and from Centroid to side Using Autocad and store it in a Excel sheet. Reduced distance from point of study and reduced level of river bed, Height above Datum at certain points are found by survey and stored. Now we will find formula to derive equivalent slope in mentioned manual and will calculate it using Excel.

Now after Equivalent Slope is calculated, We need to calculate SUG Parameters using formulas from used Report and draw SUG.

• Now when SUG is plotted we will find major coordinates for our storm duration. from this plotted graph we will see SUG coordinates 66,126 and 80 as our storm duration of 3 hours for calculating flow.

 After all parameters for SUG is calculated we move to find last 25 and 100 year rainfall and rainfall excess and flood estimation using these last 25 and 100 year's data from used Flood estimation report of CWC. For this we first need to find latitude and longitude of project which will be done by google earth pro by following steps:

• Launch Google Earth Pro and Open the Place saved for the project. Move Hand icon to the place whose latitude and longtitude is to be determined and see in the bottom right corner of the screen. we will find latitude and longtitude of desired location.

From here we will find latitude and longtitude of our project. Now using CWC Report, from Isopluvial maps we will find rainfall data of last 25 years over the region and also hourly and areal reduction factors of the rainfall. Average Rainfall for last 25 years will be calculated from this.

Thus after this we have found Rainfall of 10.80 cm for last 25 years.

• Now we will calculate rainfall excess over last 25 years rainfall.For this distribution coefficient  for storm duration is seen from the CWC report and Excess rainfall is calculated over all intermediate hours during storm and rainfall excess is arranged against graph coordinates. Maximum excess is kept against peak coordinate and direct runoff is calculated for all coordinates. Base flow for the catchment area is calculated and added to total direct runoff to Find total Flow of river.

• Now finally 25 year computation of peak flood is done by using arrangement of UHG coordinates against rainfall excess in ascending order and calculating Maximum flow at last.

Now, for estimating 100 year peak flood we will repeat steps same as done above, only change will be of taking data of last 100 years instead of 25 years.

Now, we have to enter Steady flow data of 25 and 100 year for steady flow computation. 

• Click on View/Edit Steady Flow Data option and Steady Flow Data dialog box will appear.

• In the Enter/edit number of Profiles box enter a value 2 as we whave last 25 and 100 years, 2 flow data to enter. Select the river and reach for which data is to be entered and enter the flow data in front of respective river reaches and RS.

• If you want to add more location, click on add multiple button and select desired river reaches and RS to be added and click add button. finally press OK.

• Now enter flow data as obtained for 25 and 100 year at Pf1 and Pf2 respectively. After all data is entered give boundary conditions for all stations.

After all data is entered Click on Apply Data and we need to save data now. Go to Save Flow data as option under File menu and save as dialog box will appear. Type desired name for your data and select desired folder where you want to save and press OK.

• After steady flow data is saved, go on to main window of Hec-RAS and select Perform a Steady flow simulation.  Give a name to new plan and short term identifier. Set all other data as desired and clcik on compute. After computation a dialog box will appear, click on close.

Now we can view our output with several options available on Main window like View cross sections, general profile plot, XYZ perspective plot, rating curve, Profile output table etc. In RAS Mapper we can go to Results and select the given plan and desired output such as depth, velocity etc.

Output from Steady Flow Analysis:-

Now after Steady flow analysis we go for Unsteady Analysis. 

• Go on to the Unsteady flow data option on main HEC-RAS window. Unsteady Flow data window will open.

• Now, if we want to add more RS click on to Add RS and add desired RS. Give Boundary Conditions to selected RS. For upstream RS we use Flow hydrograph and for downstream we use normal depth. Select Flow hydrograph and enter flow data at desird time and interpolate missing values.

• Now save data by File->>> Save unsteady flow data as. Give desired name and select folder to save and click OK.

Now, go onto Unsteady flow analysis button and enter all the required data for computation in appeared dialog box. click on computw then.

Thus now computations are done and we can view our results by choosing various options such as Profile plot, cross section output, hydraulic property table,  XYZ perspective plot etc.

Output after Unsteady Flow analysis:-

And Output from Steady Flow Analysis:-