RORB - Instructions - lec PDF

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School of Engineering, Civil & Infrastructure Engineering, RMIT University CIVE1145 – Assignment 2 (FLOOD ESTIMATION) The students are expected to do the assignment in Groups of 4 to 5. There are various methods to calculate flood hydrographs. The runoff-routing process is one such example. The objective of this project is for students to experience using a rainfall-runoff model to estimate the design flood hydrograph resulting from a storm with a given Average Recurrence Interval (ARI) occurring over a catchment. Assume that the catchment drains to an environmentally sensitive wetland. The flood hydrograph at the catchment outlet is required for designing the hydraulic features of the wetland. In doing this, you should become familiar with the runoff routing concept and understand the RORB software. RORB is a nonlinear runoff routing program developed by the late Professor Laurenson and Professor Russel Mein at Monash University and used widely in Australia to estimate flood flow rates from rainfall and other channel inputs (see Ch 9, ARR (1987) or Book V, Section 3.4.4, ARR (1998)). Subsequently, the program has been updated (Version 6) with new features resulting from collaboration between Monash University’s Department of Civil Engineering and Sinclair Knight Merz (SKM), with support from the Melbourne Water Corporation . The program allows for the computation of a hydrograph at any point along a catchment stream. It calculates the effects of proposed (or existing) retarding basins, dams, etc., on the hydrograph. RORB model parameters are calculated to provide the best reproduction of an observed hydrograph. The design storms are computed using the IFD curves, and temporal patterns explained in Australian Rainfall and Runoff, Vol 1, Chs 2 & 3 (ARR 1987) or Book II, Sections 1 & 2 (ARR 1998). Theory behind the RORB runoff-routing model 1. The catchment is divided into subareas bounded by drainage divides. 2. Rainfall on each subarea is adjusted to allow for infiltration and other losses. 3. A subarea rainfall excess is assumed to enter the channel network near the centroid of the subarea. 4. There, it is added to any existing flow in the channel. Then the combined flow is routed through storage by a linear or nonlinear routing procedure based on the continuity and a storage function. S = kQm where, S = volume of stored water (m3) Q = discharge from water storage (m3/sec) m = an exponent which reflects the non-linearity of the routing process. A value of m = 1 would imply a linear response. For most channel reach storage, m = 0.8 k = a coefficient related to the delay time of the storage concerned and the particular catchment being studied. k = kc kr kc = empirical coefficient applicable to the entire catchment and stream network. kr = dimensionless ratio called the relative delay time, applicable to individual reach storage.

F = a factor depending on the type of the reach Li = length of reach represented by storage i (km) dav= average flow distance in channel network of subarea inflows (km) kri = relative delay time of storage i.

ai = A= n= di =

area of the ith sub-catchment total area of the catchment number of sub-catchments distance from the centroid of the ith sub-catchment to the outlet of the catchment.

5. The combined hydrographs are routed from one node to the next node. The nodes represent       

Subarea inflow points A confluence of streams from different sub-catchments Inflow points to storage reservoirs Immediate down-stream of the storage reservoirs At any point where the significant outflow from a stream occurs At any gauging station, sites for which design flows are required or other matters of particular interest, and Catchment outlet.

The program is designed to run in 3 modes. In the fitting or calibrating mode, the values of kc and m and loss rates (initial and continuing) can be altered to make the calculated hydrograph resemble the observed hydrograph as closely as possible. The calibrated kc and m values are verified using an independent set of observed rainfall and hydrograph data in the test mode. The design mode run uses the Intensity-Frequency-Duration (IFD) relationships and temporal patterns obtained from ARR as design storms and the fitted k c and m values as catchment parameters to predict the design hydrograph. The program requires the following data: 1. Sub-catchment areas and properties 2. Rainfall hyetographs over subareas 3. Channel reach length represented by the storage (to calculate routing delay times along the catchment streams) 4. The routing vector which controls the computer model operation. The runoff from each sub-catchment in each time period is calculated and then treated as an output hydrograph at the sub-catchment outlet. It is then routed, stored, or added to the inflow hydrograph according to the specified sequence given in the routing vector with the appropriate time delay. The RORB V6.14 runoff routing program is available on the Computer Lab (C drive) under RORB. Students can also download the program and the manual from http://www.harconsulting.com.au/ Read the RORB user manual 

Sections 2.1, 2.2, and 2.3 – these sections give details of how stream systems and catchments are represented in the RORB program.

 

Sections 4.1 and 4.2 – these sections give the control codes which represent the stream network. Chapter 5 describes in detail how the input data file is prepared.

To familiarise the model, sample data files for the South Creek catchment have been created as SCKFIT.cat and SCKMAR56.stm and are given in the RORB user manual (Sec. 10.4). A map of the South Creek catchment is also shown. To familiarise with the model, run RORB using the South Creek data as a FIT run to determine optimum values of k c and m. Change both kc and m separately, and observe how these parameters influence the hydrograph shape. See Activity 4D in the Learning Guide. Exercise Calculate the design hydrograph at the outlet of the given catchment resulting from a storm with an average recurrence interval (ARI) of 100 years, using the RORB model and the Rational Method. a. Each catchment has 4 rain gauges. Use the Thiessen polygon method to calculate the areal uniform rainfall of the given catchment. For the given location, obtain IFD curves and the design storm patterns (temporal patterns) for an ARI of 100 years using Graham Jenkin’s AUSIFD program V(2) (Uploaded on the myRMIT CIVE1145 Blackboard or use Bureau of Meteorology, free software at http://www.bom.gov.au/water/designRainfalls/ifd-arr87/index.shtml It is essential to report the calculation procedure for temporal patterns and the assumptions used. b. The rainfall hyetograph data from two storms and the corresponding streamflow data are given in the Table. Calculate the following and compare results with the results obtained from the RORB model.   

Surface runoff hydrograph (separate baseflow) Excess rainfall hyetograph (or surface runoff volume) Initial loss and continuing loss

Discuss the reasons for the difference in manual and model calculated values. c. Use of the RORB model to calculate the flood hydrograph. The following steps need to be pursued when running the RORB program: Creating Data file Sub-catchment boundaries, nodes, and storage are marked in the catchment map. Measure subcatchment areas and reach lengths between nodes to create the input data file. Prepare the input data file for your catchment as given in the user manual (A sample data file is provided in tutorial slides). To determine optimum values of kc and m use one set of storm data given in Table 2. Write the control vector as given in Sections 4.1 and 4.2 in the user manual. When saving the data file, you have to save it as an extension ‘.dat’. Note: Create the data file using the notepad and save it as an extension ‘.dat’. The first line of the input data file has to be the top row of the page (do not keep a blank line at the top). All subsequent lines have to start from column 1 of each line.

FIT run Once the data file has been created, execute the model using the command RORB (Read Sections 7.2 of the user manual). Independently change both kc and m until you obtain a good fit of actual and estimated hydrographs. Observe how these parameters influence the hydrograph shape. Click on the RORBWin icon to start the program, and then on ‘File’, ‘New’, and ‘Run specification’ to bring up the Run Specification screen.

Click on ‘Single input file (Original RORB format)’ as we have created a single data file with both catchment data and storm data. (If necessary, you can also have two separate files for catchment information and storm information). Browse the computer and select your input data file to run with RORB. Other choices (i.e. loss model etc.) on the screen are left at the default options for this exercise. Pressing the ‘OK’ button brings up the Parameter Specification window. For this Window, you need to give kc and m values. Select arbitrary kc and m values. A value for initial loss also has to be provided. Press the ‘Plot’ button. The program calculates the respective continuing loss, as shown in the screenshot given below. You can superimpose the ‘Parameter Specification” screen on the hydrograph screen by pressing the ‘►’. Change the Kc and m values until you get a good fit between the actual (observed) and calculated (estimated) hydrographs.

You can obtain details about the catchment, rainfall excess, model parameters, comparison between actual and calculated hydrographs by clicking on to ‘View Text Output’ button on the toolbar. TEST run Create another data file with the second set of storm data. To verify the fitted parameters, run the RORB model with the parameters obtained from the fit run (Initial loss could vary). Compare the actual and estimated hydrographs (Read section 7.3 in the user manual). If the fit is satisfactory, kc and m parameters are now considered invariant and fixed as the catchment parameters. If not, find a new set of k c and m parameters from the fit run until satisfactory results are obtained from FIT and TEST runs. DESIGN run When the model has been fitted and tested, the kc and m parameters are constant for this particular catchment. Use these parameters for design purposes. Run RORB, assuming initial loss equal to 0 and continuing losses obtained from the FIT run. Note you need to change the ‘Print’ control code of the catchment input data file in the design run (See Table 4.1 in the manual). As the storm duration to produce the maximum peak discharge is unknown, it is necessary to run the model with different design storms calculated according to Australian Rainfall and Runoff. Obtain Intensity-Frequency-Duration curves and the design storm patterns (temporal patterns) for the given location and for a recurrence interval of 1:100 years using Graham Jenkin’s AUSIFD program V(2) (Uploaded on the myRMIT CIVE1145 Blackboard or use Bureau of Meteorology, free software at http://www.bom.gov.au/water/designRainfalls/ifd-arr87/index.shtml. The RORB model also has a facility to calculate the IFD curves and temporal patterns. However, as a learning exercise, I would like you to use the manually calculated values. Submit copies of input data files and output graphs for Fit, Test, and Design (at least one for the design storm) runs.

(d) Plot design peak discharge (Q p) vs. storm duration to find the storm that produced maximum peak discharge. (e) Prepare a report giving all calculations (if repetitive calculations, provide a sample calculation), assumptions made, and a copy of the data file and representation of observed and estimated hydrographs. (f) Apply Rational method and compare results with the results obtained from the RORB model. Provided Information  Map of the catchment with sub-catchment boundaries marked. The rainfall hyetograph data from two storms and the corresponding streamflow data for each catchment (Fig. 1 – Distributed in class and placed on Canvas.  Catchment location assigned for each group (Table 1)  Assume catchment to be pervious, all channels are in natural condition, and rainfall is uniformly distributed.  The rainfall hyetograph data from two storms and the corresponding streamflow data are given in Tables 2 and 3. REFERENCES  Engineers Australia (1987 & 1998): Australian Rainfall and Runoff Vols. 1 and 2  Laurenson, E.M., Mein, R.G. and Nathan R.J. (1999): RORB Version 5 Runoff Routine Program User Manual (Monash University, Dept. of Civil Engineering)

Table 1 – Catchment location

Grp No.

Location

Catch No

Grp No.

Location

Catch No

1 & 21

Adelaide

1

11 & 31

Queenstown

1

2 & 22

Alice Springs

2

12 &32

Sale

2

3 & 23

Armidale

3

13 & 33

Shepparton

3

4 & 24

Bairnsdale

4

14 & 34

Sydney

4

5 & 25

Ballarat

1

15 & 35

Wodonga

1

6 & 26

Broken Hill

2

16 & 36

Mount Gambier

2

7 & 27

Melbourne

3

17 & 37

Perth

3

8 & 28

Canberra

4

18 & 38

Wagga Wagga

4

9 & 29

Wollongong

1

19 & 39

Horsham

3

10 & 30

Gippsland

2

20 & 40

Geelong

4...