Exercise 3: Estimation of design flood

A synthetic sequence of extreme precipitation has been derived by meteorologists (Table 1). Now it is your task to estimate the flood that this sequence would cause for the River Fyris at Vattholma (Uppland). In other words, you should estimate a design flood. You have decided to use the HBV model to solve this problem. Some friendly hydrologist put all necessary files together (most important the 'ptq.dat'–file with areal precipitation, temperature and observed runoff for an eleven-year period), but the model is far from well-calibrated. 

You have to complete three steps:

1) Calibration

Change the following parameters in order to get an as good fit as possible between observed (blue) and simulated (red) runoff: TT, CFMAX, SFCF, FC, BETA, LP, K1, K2, PERC, MAXBAS (K0 och UZL should not be used (i.e. put them to zero), do not change the values for for CFR, CWH och CET (0.05, 0.1, 0.1)). Use the period 810901 to 870831 for calibration (with the 'warming-up' period starting at 810101). 

2) Validation

Before you use your calibrated model for any prediction it is important that you test your parameter set for an independent time period. Use the period 870901 to 911231 for this test. Is the fit worse? Can you give an explanation? How will your design flood be affected? 

3) Simulation of flood

1. Make a backup-copy of ptq.dat 
2. Open the file ptq.dat in a text editor (or Excel) 
3. Choose a period for which you replace the observed precipitation by the synthetic sequence (Table 1 or file Precipitation_data.xls) 
4. Save the file (if you use Excel choose the format '*.csv' (colon-separated), but use the name "ptq.dat") 
5. Restart HBV light and run the model. Check the peak value of your simulated flood. 
6. Return to the backup-file, choose a different period and continue with 2. Do this 5-10 times. 
7. Answer the questions: What influences the size of the simulated flood?nder which conditions becomes the simulated flood largest/smallest? 

Exercise 4

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