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Why the rainfall-runoff process models are called physically based models?
- They try to represent the physical processes observed in the real world. They are ‘Deterministic’ models based on process descriptions (rather than data) and are entirely predictable.
- Typical processes simulated are:
- effective rainfall
- overland flow
- groundwater flow
- channel flow
Give few examples where rainfall-runoff process models are used to solve water issues.
- Determine expected inflows for a storage area such as the Thomson Dam.
- Predict and mitigate floods, landslides or droughts such as QLD and central VIC floods early 2011.
- Designing an urban drainage system such as Little Collins, Elizabeth to Queen, or a new subdivision such as the Peregrine Heights in UFTG.
What data is required in rainfall-runoff process models to convert daily runoff values from the stream gauging station?
Interception (vegetation), evapotranspiration (PET and MAPET), rainfall and MARAIN. streamflow, humidity
What is the input data required to calibrate the SYMHYD and AWBM models?
- SYMHYD: estimates daily streamflow from daily rainfall and areal potential evapotranspiration data. (RRL program)
What is called model calibration and validation?
- Calibration: process of adjustment of the model parameters
- Validation: comparison of model results with an independent data set without further adjustment to the parameters
What are the parameters involved with the SimHyd model?
- INSC, interception store capacity (mm)
- COEFF, maximum infiltration loss (mm)
- SQ, infiltration loss exponent
- SMSC, soil moisture store capacity (mm)
- SUB, constant of proportionality in interflow equation
- CRAK, constant of proportionality in groundwater recharge equation
- K, baseflow linear recession parameter
What are the parameters involved with the AWBM model?
- Surface Storage Capacities
- Partial Areas represented by Surface Storages
- Base flow Index
- Daily Baseflow Recession Constant
- Daily Surfaceflow Recession Constant
- Current Volume in Baseflow Store
- Current Volume in Surface Routing Store
Explain the concept of the AWBM model with a schematic diagram.
What is called Baseflow Index (BFI)?
It is one of the Baseflow parameters in the AWBM RRL model. (The other parameter is the baseflow recession constant.) The BFI determines how much of the runoff is baseflow.
Explain the concept of the SimHyd model with a schematic diagram.
What are the component runoffs
to generate the total runoff in SimHyd model?
Baseflow and Surface
What is meant by surface moisture capacity and soil wetness?
- SW: soil moisture level divided by soil moisture store capacity
How recharge is estimated in SimHyd model?
- It is groundwater store that is estimated as a linear function of the soil wetness.
- = recharge coefficient x soil moisture fraction x infiltrationAfterinterflow
Explain why catchment characteristics are essential in rainfall-runoff process modelling?
catchment characteristics are invaluable for setting realistic bounds on model parameters as well as checking the fluxes out of the model area
Explain the issues that are needed to consider in the preparation of rainfall data for rainfall-runoff process models.
- ensure that the best possible data set is used to speed up the calibration process
- ensure all rainfall sites are gap filled
What is the difference between potential evapotranspiration and actual evapotranspiration?
- PET: evapotranspiration that would occur from
- another well vegetated surface under existing atmospheric condition and when moisture supply is not limiting
- AET: evapotranspiration that occurs under actual soil, ground-cover, and water-availability conditions
Discuss the issues that are needed to consider in the preparation of streamflow data for rainfall-runoff process models.
- 1 How height data is collected
- 2 How stable is the rating at the site
- 3 The relationship between height i.e. how sensitive is a flow estimate to a change in height.
- 4 Looped ratings i.e. where the rating on the rising and falling limbs of hydrographs are different.
- 5 Sticking gauge i.e. how believable is it at low flows.
- 6 The highest rated flow.
Why the data record divided for calibration and verification periods is a preferred method over calibration for entire period?
gives a way of assessing the robustness of the model for periods outside of the calibration period.
When calibration will be biased towards wet periods?
If the dry extreme is above the lower third of rainfall and/or the mean of the calibration period is one standard deviation above the mean of the entire period of record then it is likely the calibration will have a bias toward wet periods. This will mean that the model will perform well during wet periods but is likely to overestimate flows during dry periods.
When calibration will be biased towards dry periods?
If the wet extreme is below the higher third of rainfall and/or the mean of the calibration period is one standard deviation below the mean of the entire period of record then it is likely the calibration will have a bias toward dry periods. This will mean that the model will perform well during dry periods but is likely to underestimate flows during wet periods.
Why model warm-up period is required?
it’s a period where the contents of the storages reach a storage depth that is within 1% irrespective of the value of the model parameters.
Why objective function(s) are used in rainfall-runoff process models?
What are the criteria for the selection of optimizers and objective functions?
What is meant by parameter sensitivity?
If the model is significantly affected by a particular parameter than the focus of calibration should be on that parameter.
What are the functions of the optimizers in the process models? Discuss.