AWBM modelling
This assessment is designed to test your achievement of course objectives 4 to 6 focussing on model calibration and rainfall-runoff modelling. This assignment is based on a hypothetical project and is divided into two main activities:
- Familiarisation with AWBM software –described in Section 2
- Calibration of AWBM for the Caboolture River catchment – described in Section 3
Details of the submission requirements for Assignment 1, as well as how the assignment will be marked, is described in Section 4.
Activity 1:
This activity is assessable and is included as a way for you to trial the RRL software before embarking on the full calibration exercise (See Section 3). Refer to Section 4 on the submission requirements for this part of the assignment.
Open the Jardine River project file (AWBM_Jardine.jobf) and use the RRL software to complete the following:
- For the available data from 1974 to 1989, what is the average annual rainfall, evapotranspiration and observed runoff for the Jardine River?
- Setup the following simulation periods: Warmup from 1 January 1974 to 31 December 1974 and a calibration period to 31 December 1986. Use the SCE-UA optimisation method and the RMSE objective function to optimise the AWBM. What are the AWBM calibrated parameter values that are generated from this optimisation? In terms of the degree of fit with the observed data, what are the RMSE, Nash-Sutcliffe E and Coefficient of Determination (Correlation) values?
- Extract a scatter plot of monthly observed and predicted runoff. Also provide a ‘zoomed in’ plot of observed and calculated runoffs covering the 1976 wet season.
As well as becoming familiar with the use of RRL, you should also understand the AWBM model algorithms (see good modelling practice Module 2.4). In particular, you should gain an appreciation of how the model results change when a parameter value is adjusted (see the ‘electronic control box’ analogy Module 2.3). This understanding will assist you in calibrating the AWBM to measured streamflows. Complete the following: - The scatter plot and 1976 wet season plot generated from the above Step 3 provides a benchmark or starting point to compare how the AWBM streamflows may change in response to adjustment of the AWBM parameters. The total runoff is also a useful measure of model results.
- Taking each AWBM parameter in turn, rerun the AWBM with a higher and lower parameter value and regenerate the above outputs. Keep the values of the other parameters constant, so the effect of the selected AWBM parameter is isolated. You may need to substantially vary some parameters.
- Describe the effect of adjusting each AWBM parameter on the plotted results. Describe, based on your knowledge of the AWBM model structure, why this effect has occurred.
AWBM Validation –Caboolture River streamflows
This part of the assignment involves the calibration and verification of an AWBM of the Caboolture River catchment, based on the modelling practices and validation procedures described in the Study Book Module 2 and 3. A gauging station is operated by the Queensland Department of Natural Resources and Mines (QDNRM) on Caboolture River at Upper Caboolture (GS 142001A). Details at the streamgauge can be found at the Qld Government Water Information Monitoring Portal. https://water-monitoring.information.qld.gov.au/
Gauge Station 142001A started operating in 1965. The purpose of the validated AWBM is to synthetically extend the length of streamflow data at the streamgauge by making predictions of the monthly runoff volume from the period from 1940 onwards. These estimates can be made from the rainfall and evaporation data that is available. The extension of measured streamflow data based on simulated estimates is commonly used in engineering hydrology to obtain a more representative measure of the frequency and occurrence of wet and dry extremes. The AWBM is considered to be a suitable model for this type of simulation, especially if calibration data is available.
Check and Prepare Input Data
BOM Climate Data Online provides a map showing rainfall stations in the local region of the Caboolture River catchment. Rainfalls are also measured at the streamgauge. Identify potential rainfall sites based on proximity and data availability. The hydrology data from BOM have quality codes indicating missing data or other problems that may affect the reliable use of the data. It is thus critical to review the data and to identify time periods when data is of poor quality or missing and unsuitable for modelling. This is essential to have confidence in the simulation periods that are selected to validate the AWBM.
The River Analysis Package (RAP) freely available from the eWater Toolkit website is useful software that can be used to identify gaps in timeseries data and plot the data. It also has the capability to fill in missing data by linear interpolation or by multiple linear regressions using data from other rainfall gauges.
Check and Prepare Inout Data:
Download the historical streamflow data and identify missing periods and/or poor quality data. Evaluate the likely accuracy of the streamgauge rating curve based on the number and magnitude of the gaugings that have been done. This will provide an indication of the overall quality of the streamflow discharges derived from the rating curve. Identify periods of record that would be useful to test the AWBM streamflow estimates and generate a daily discharge file to load into AWBM. Ensure that days with missing data are assigned the correct RRL value (e.g. -9999).
Generate a topographic base plan using the QTopo website. Draw the catchment boundary of the Caboolture River gauge and the locations of nearby rainfall stations. If you do not have access to mapping or CAD software, it is suggested that a pdf editor will be adequate to do this task. PDF XChange Editor has basic polygon drawing and measurement tools. A free version can be downloaded from Tracker Software.
Plot the rainfall timeseries and check the available rainfall data for completeness and quality. Tabulate time periods for each station that you consider have data suitable for the AWBM modelling.
If rainfall sites have comparatively small gaps of missing data, use RAP to infill these gaps generate a catchment-average daily rainfall input file for AWBM
- Obtain monthly potential evapotranspiration from BOM online maps. Generate a daily evapotranspiration input file for AWBM. RAP software may be useful for this purpose.
AWBM utilises daily rainfalls representative of the spatial average (or areal rainfall) across the catchment, whereas the measured rainfall data are point rainfalls. Thus, a geographical spread of rainfall stations should be selected that allow you to estimate the areal rainfall – stations outside of the catchment boundary may be required.
The BOM Water Data Online website includes the Caboolture River streamgauge within its compilation of Australian water information and also shows useful information for this site.
Calibrate and Verify the AWBM
The rainfall, evapotranspiration and observed streamflow data used for AWBM need to be loaded into the RRL. After the data files have been inputted into RRL, make use of the Input statistics to check that no errors have been made.
The setup and validation of the AWBM involves the use of three different approaches:
- Testing of the AWBM using ‘initial guess’ parameter values adopted from available publications.
- Calibration using AWBM Auto Calibration
- Calibration using a selected optimisation method
Details of the three approaches are provided in Table 3.
AWBM Sensitivity Analysis
Computer modelling always carries a level of uncertainty and one approach to address uncertainty is to undertake a sensitivity analysis of the model parameters. The simplest approach is referred to as a ‘one-at-a-time’ analysis. This involves selecting a parameter, increasing the parameter value by a fixed proportion (typically +10%), rerunning the model (keeping the other parameters to ‘calibrated’ values) and reporting the model results. This process is repeated for a reduction of the parameter value (typically -10%). The whole process is then repeated for a different AWBM parameter until the sensitivity of model results to each individual parameter is established.
Use the selected AWBM parameter set as the starting point for the sensitivity testing. From the sensitivity analysis, you should be able get an appreciation of which parameters are more important in terms of their effect on model outcomes. This will guide you on which parameters should be closely checked (refer next task).
Sanity Check of AWBM Outputs:
Sanity checks should (always) be made to give you confidence that the AWBM model is providing acceptable results and that no major errors of analysis or data input/output has been made. The sanity checks should include:
- Checking that the selected AWBM values are consistent with the underlying principles of the model. For example, the store capacities should increase in size (i.e C1<C2<C3)
- Computing the observed and predicted mean annual runoff (ML/yr) for the full streamflow period. As a guide, these mean estimates should match to within 5%.
- Compare the above estimate with the average annual runoff for the catchment based on Boughton and Chiew (2007).
- Closely inspect how well AWBM daily flow estimates match recorded flows for a selection of large individual floods within the streamgauge record. This includes the peak discharge and the recession curve of the flood.
- Compare flow duration curves for observed and predicted daily flows. These curves can be prepared within RRL.
These sanity checks may necessitate some adjustments to the AWBM parameter values. Manual changes to AWBM parameter values can be made in RRL.
Generate Monthly Streamflows:
Once you are satisfied with the accuracy of model predictions, run the AWBM with the final set of parameter values to generate monthly streamflows for the period from January 1940 to December 2017. Tabulate the annual runoff for each year and estimate the average annual runoff.
Also compute and plot the average flow volume for each month of the year to show how flows vary seasonally within Caboolture River. (Note, these volumes are the average of each calendar year over multiple years e.g. January average). The RAP software can generate monthly average statistics or this could be done in Excel.
Tabulate the annual runoff for each year and estimate the average annual runoff.