Due date: 25 August 2022
Weighting: 25% (250 marks)
This assessment is designed to test your achievement of selected learning objectives of Modules 2 to 5. In particular, the assignment involves flood frequency analyses and working with historical streamflow and rainfall data. The assignment is intended to reinforce and extend your knowledge on hydrological methods and the uncertainty associated with design flood estimation.
Due to intense heavy rainfall which lasted for several days in February 2022 has resulted in damaging flood conditions similar to 2011 floods particularly in Southeast Queensland. Many areas in Lockyer Valley Regional Council have been affected by 2022 floods. Floodplain planning and risk management is very important for responding to emergency situations. Floodplain planning and Risk Management involves a detailed modelling for determining flood levels, extent, velocity data and associated flood maps within the council area. Assuming that Lockyer Valley Regional Council has commissioned a project for a detailed Floodplain planning and Risk Management studies, estimating design flood through flood frequency analysis is one of the key parameters required in the project. In this assessment the focus is given in design flood estimations based on the content covered in modules 2 to 5. We are considering the study area as Lockyer Creek at Helidon (143203C) to provide best estimates of design flood corresponding to a range of Annual Exceedance Probabilities (AEPs) 50%, 20%, 10%, and 1%.
The flood frequency analysis (FFA) will be based on consideration of the outputs of three techniques: Annual Series, Partial Series and the new Regional Flood Frequency Estimation (RFFE) developed as part of the Australian Rainfall and Runoff ARR 2019.
The assignment is based on the following main tasks:
- Obtaining and reviewing the streamflow data
- Annual Series FFA based on fitting a Log Pearson 3 (LP3) distribution to annual discharge maxima
- Partial Series FFA based on monthly discharge maxima
- Design discharge estimation using the RFFE method.
- Compilation of the estimates and selection of a set of design flood discharges, based on consideration of the above outputs
- Assessment of the rainfall frequency associated with the February 2022 flood event
- Preparation of an assignment report
2. Assignment Tasks
2.1 Streamflow Data
Access the Portal and find the stream gauge data. Tabulate the following basic gauge information: location (latitude and longitude), the catchment area, when stream gauging started, when rainfall measurements started, the maximum observed instantaneous discharge and when this occurred, and the maximum observed daily total rainfall and when this occurred.
The hydraulic control and associated rating curve are also of interest. Include in your report an images of the creek cross section at the stream gauge, the comparison plot of gaugings and latest ratings undertaken. How many gaugings have been done up to 2022? What is the highest gauging (level and discharge) and how does this compare with the highest recorded flood? Make a comment of the adequacy of the rating curve based on this information, especially the reliability of the discharges associated with the largest floods.
Download the monthly discharge data from the 1/10/1988 to 30/09/2021. Generate a timeseries plot of monthly peak discharges. What percentage of the data is missing (code 255)?
2.2. Annual Series FFA
The Annual Series FFA is to be first undertaken on the following basis:
- Include data for all water years from the start of record to the end of 2020/2021 water year( Water year in Australia is: 1st October to 30th September)
- Exclude from the analysis the water years that have 4 or more months of missing flow data. ARR recommends several approaches to handle missing data, but this simple exclusion method will be used. This may require an adjustment to the number of years of available data, N that we use in our analysis.
- Fit a LP3 distribution to the Annual Series, estimate 5% and 95% confidence limits and prepare a flood frequency chart. Extract the design discharge estimates for the specified AEPs.
Please observe and report if you found any skew(positive or negative). Skewness may be due to the presence of abnormal discharges/outliers. Including these floods may result in a poor LP3 fit to the much higher major floods, and thus influence the design discharge estimates in this range. Please follow the recommendations provided in ARR on dealing with outliers while fitting the series for flood frequency analysis.
2.3 Partial Series FFA
The Partial Series FFA is to be undertaken on the following basis:
- Use the monthly discharge maxima to extract the Partial Series. Monthly discharge maxima are acceptable for small catchments as typically the peaks between months are sufficiently separated by time to be hydrologically independent.
- Use the monthly discharge data from the start of record to the end of the 2020/2021 water year.
- For months with missing data, assume that no floods occurred during these periods. This assumption differs to that made in the Annual Series, so may give a different N to use in the analysis. The value of N can be non-integer.
- It is recommended that Partial Series threshold should be selected such that K (the number of independent flood peaks above the threshold) equal to N in defining the Partial Series threshold.
- Plot the Partial Series and, from fitting a suitable regression line, provide design discharge estimates for the specified AEPs. Please consider removing outliers and see how this will influence your estimations.
- Prepare a Partial Series flood frequency chart
2.4 RFFE design discharge estimates
You are requested to use Regional Flood Frequency Estimation (RFFE) approach to estimate design peak discharges. An online tool has been developed to generate RFFE estimates that depend on catchment location and this website can be found at https://rffe.arr-software.org/
Generate a set of design discharge estimates for the catchment of Lockyer Creek at Helidon using the RFFE method. Also provide a map showing the catchment boundary and the location of the catchment centroid.
Topographic map can be generated from the Queensland Government’s online QTopo mapping site (http://qtopo.dnrm.qld.gov.au/Mobile/). You can download the contour map of the catchment area using the location coordinates of the stream gauge site available inthe water monitoring portal. Define the catchment boundary and measure the catchment area (you may use the PDF-Xchange Editor tool or any other sophisticated tool). Compare your estimated catchment area with the area provided in the Water Monitoring Portal. Also, locate and mark the centroid of the catchment on the topographic map.
2.5 Design Rainfall: Assessment of February 2022 flood rainfalls
The largest recorded floods have an impact on the fitting of a LP3 probability distribution to the Annual Series, more so than the frequent minor floods. It is thus worthwhile investigating the top ranked floods in some detail.
BOM have prepared detailed reports on notable floods in Australia and Queensland reports are available from http://www.bom.gov.au/qld/flood/fld_reports/reports.shtml. Please look if there are any flood reports for the relatively small Lockyer Creek.
Rainfall measurements are recorded at the stream gauge and the more recent February 2022 flood was selected for analysis. This is understood to be second ranked flood on record. The objective of the analysis is to determine the frequency of the observed rainfall that fell during the February flood event.
The rainfall analysis involves the following tasks:
- Access the Water Monitoring Portal, find and plot the recorded flood hydrograph for the February 2022 flood. Include in the plot at least 2 days of flow record after the flood peak and at least 3 days of record prior to the peak. Generate a plot of rainfall data for the same period of time.
- From the plots, you will be able to identify the period of rainfall that was associated with the flood.
- Estimate the time of concentration of the Lockyer Creek at Helidon catchment (refer to Section 5.3.2 of the Study book).
- Access the BOM IFD site and download the 2016 AR&R IFD data for the nominated stream gauge location (http://www.bom.gov.au/water/designRainfalls/revised- ifd/?year=2016). It is appropriate to use this data as it represents the latest estimates of rainfall frequency. Provide the Rainfall IFD chart (rainfall in mm/hour) for different AEPs.
- Estimate the approximate AEP of the observed rainfall depth for the duration corresponding to the time of concentration (round off to the nearest hour). Estimate the corresponding AEP of the 2022 flood discharge
2.6 Compile and select design discharge estimates
Compile the design discharge estimates for the Annual Series, the Partial Series and RFFE analyses as a table. Plot the discharge estimates on the same graph against specified AEPs.
Select design discharge estimates for each of the required AEP. Provide statements that justify the choice of design discharge for each AEP.
Your submission for Assignment 1 should include:
- A detailed report that documents all the tasks required as part of the Assignment-1. A marking scheme is provided as Table 1. Use this marking scheme to check that you have addressed the full scope of the work. If an element of the assignment has not been documented in the file report than no marks will be given for that element.
- An Excel sheet with all the calculations shall be submitted. Electronic submission of the report and excel sheet should be through the study desk.
- Part of the available marks has been allocated to reward reporting that is well set out and easy to follow. Submissions that are untidy and/or poorly structured and thus difficult to assess will attract less marks for this element.
The following filename convention shall be used: YourName_Ass1.pdf and YourName_Ass1.xlsx,where Your Name is your first and last names.
Penalties for late assignment submission:
If an Assignment is submitted after the published deadline without an approved extension of time, the maximum Mark will be reduced as a consequence. In this case, the available Mark is reduced by 5% (of the original available Mark) for each Calendar Day or part day that the Assignment is late.
An Assignment submitted more than one (1) week after the due date will have a Mark of zero recorded.
For students with an approved extension, a zero Mark will be awarded for an Assessment Item if it is submitted after an approved extension date.
4. Marking Scheme
The marking scheme proposed for Assignment 1 is presented in Table 1.
Table 1: Assignment 1 Marking Scheme
|Annual Series FFA|
|Basic streamgauge data and rating curve||25|
|Missing data (timeseries plot and % missing)||10|
|Annual Series including low floods (missing data table, ranked discharges table)||20|
|Annual Series statistics||10|
|Annual Series FFA charts and design discharge estimates||30|
|Partial Series FFA|
|K and threshold discharge||5|
|Partial Series discharge table||10|
|Regression plot, fitted equation||10|
|Partial Series FFA chart and design discharge estimates||20|
|Catchment plan showing boundary and centroid||20|
|RFFE design discharge estimates||10|
|Assessment of February 2022 flood rainfalls|
|Flood hydrograph and rainfall plots||10|
|Table of February 2022 storm details||10|
|Selection of design discharge estimates|
|Table of discharge estimates||5|
|Selection of design discharges with justification||10|
|Assignment EXCEL spreadsheet||10|
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