ARR Data Hub
Before constructing a DRAINS model, users will need to obtain data for a location from the ARR Data Hub and the BOM website, starting with the Data Hub (data.arr-software.org). After obtaining the necessary data it can then be inputted into DRAINS using the Rainfall Ensembles property sheet.
To demonstrate the process of obtaining the necessary data, the example location considered will be Taree NSW and the selected hydrological model will be the ARR 2019 recommended Initial Loss - Continuing Loss (IL-CL) model.
Search for 'Taree NSW' using the search bar provided on the ARR Data Hub, then manipulate the map shown until the blue pointer is located at the site. The latitude and longitude will appear in the boxes to the left of the screen.
Next select the boxes for Storm Losses, Temporal Patterns, BOM IFD Depths, Median Preburst Depths and Ratios and Interim Climate Change Factors, then press Submit.
The ARR Data Hub can show the selected zone for Temporal Patterns being applied by clicking on the show link:
Information will appear that includes Storm Losses, Temporal Patterns | Download (.zip) and a 'click here' link to obtain the 2016 I-F-D data on the BOM Website based on the coordinates entered into the ARR Data Hub.
Storm Losses (applicable for the IL-CL model)
The ARR 2019 guidelines suggest that initial loss and continuing loss values from the ARR Data Hub should only be used in the absence of available local data and that it is essential that assumptions about losses in stormwater models are based on the assessment of local conditions.
As ARR 2019 currently only provides temporal patterns for the Storm Burst, then the remaining Initial Loss within the Burst of the storm must be calculated. This is calculated by reducing the Storm's available Initial Loss (ILs) by the depth of Preburst Rainfall.
The equation is shown below, along with a figure from ARR.
Equ 1: Initial Loss Burst (ILb) = Initial Loss Storm (ILs) - Median Preburst Depths
ARR 2019 Figure 5.3.5 Distinction between Storm and Burst Initial Loss
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If obtaining data from NSW, there are further specific items to consider as detailed here: https://data.arr-software.org/nsw_specific. In summary NSW OEH has developed a guide (www.environment.nsw.gov.au) to assist Councils and consultants undertaking studies under the NSW Floodplain Management Program to transition to ARR 2019. Practitioners in NSW should use a hierarchical approach to the loss and pre-burst estimation. This hierarchy goes from 1 (most preferred) to 5 (least preferred) as indicated in Table 1 on the Data Hub. This guide is supported by ARR 2016 Case Study - Urban and ARR 2016 Case Study - Rural. Note the DRAINS demonstration in the Urban case study report was prepared on an early ARR 2016 version of DRAINS. Please refer to this Help System for current application of ARR 2019 procedures.
Where good local initial loss data is not available (Cases 4 and 5) the Probability Neutral Burst Initial Loss values determined in the WMAWater 2019 study and as available through the ARR Data Hub should be used in all instances unless a detailed Monte Carlo assessment of pre-burst and losses has been carried out.
For NSW Studies, the ARR Data Hub currently advises that if the Continuing Loss (CL) values are to be used from the ARR Data Hub, then they must also be multiplied by a factor of 0.4 & that Probability Neutral Burst Initial Loss (ILpnb) values must be used instead of Median Preburst Depths and Ratios.
In order for software to support the Probability Neutral Burst Initial Loss (ILpnb) values, the ARR Data Hub provides Transformational Preburst depths via a Download.txt button at the bottom of the ARR Data Hub results page after selecting Storm Losses & Median Preburst Depths & Ratios.
The equation to calculate Probability Neutral Burst Initial Loss is.
Equ 2: Probability Neutral Burst Initial Loss (ILpnb) = Initial Loss Storm (ILs) - Transformational Preburst Depths
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If obtaining data from VIC, there are further specific items to consider as detailed here: https://data.arr-software.org/vic_specific.
Following the release of ARR2019, Melbourne Water and DELWP commissioned a study to benchmark the performance of ARR2019 in the state of Victoria. Below is the executive summary of that report, otherwise view the full text.
On the basis of the investigations described in the report, it is recommended flood estimates obtained using ARR2019 Data Hub regional information should be derived using the 75th percentile pre-burst rainfall (in lieu of the median value) in combination with unmodified Data Hub values of initial and continuing loss. Given the distribution of catchments considered, this recommendation is only supported by information obtained for catchments within loss region 3.
While obtaining values from the ARR Data hub it notes that “these losses are only for rural use and not for use in urban areas”. Book 5 Section 3.5.3.2.1 of the ARR 2019 Guidelines states:
“Based on the limited available information, it is recommended that a median ILs of 60% to 80% of the recommended rural catchment ILs be adopted.”
This advice was based on the assumption of lumped impervious (ICIA) & pervious areas within a catchment and simply categorised as “remaining area”. These areas are separated in DRAINS so this ARR recommendation is not directly applicable to Horton ILSAX or the IL-CL as from version 2019.09. Refer to IL-CL Hydrological Model for more information on applying the IL-CL hydrological model in DRAINS.
Book 5 Section 3.5.3.1.2 recommends to adopt a storm initial loss of between 1 to 2 mm for EIA and continuing losses for EIA can be assumed to be zero.
Book 5, Chapter 3, Section 5 states that regional analysis of a small number of urban catchments provides estimated initial losses of 1 to 3 mm for EIA and 20 to 30 mm for indirectly connected areas in sub-catchments and estimated median continuing losses were 2.5 mm/hour in South East Australia and 1 to 4 mm/hour elsewhere.
Following is example rural loss data provided from the ARR Data Hub:
Note: the Storm Losses and Median Preburst Depths and Ratios are only applicable to the Initial Loss Continuing Loss hydrological model.
Note: high initial loss values may result in little to no runoff in frequent storms where the specified initial loss value exceeds the available total rainfall depth.
Note: NSW specific guidance on the Data Hub currently advises that if Continuing Loss (CL) values are to be used, then they must also be multiplied by a factor of 0.4 & that Probability Neutral Burst Initial Loss values must be used instead Median Preburst Depths.
Note: VIC specific guidance on the Data Hub currently advises that if Continuing Loss (CL) values are to be used, and the site is located within Region 3, then the unmoidified loss values should be used with the 75% Pre-burst Depths must be used instead Median Pre-burst Depths.
Temporal Patterns
Find and click on the Temporal Patterns Download (.zip) link and save the .zip file to a convenient location. Extract the contents from this .zip file which will go to a folder of the same name. There will be two .csv files, of which we will be importing the file with the word 'increments' in the title.
2016 IFD Depths
Next find and click on the link to obtain the 2016 I-F-D data from the BOM site. You will be transferred to the Bureau of Meteorology site (www.bom.gov.au/water/designRainfalls/ifd), and a window showing the I-F-D Table will appear.
Click the second leftmost button above the map to download a .csv file containing both Frequent (AEP) and Very Frequent AEP (EY) rainfall depths. Save this file.
Median Preburst Depths
As discussed in the Storm Losses section above, Preburst depths and ratios are needed for the IL-CL model to reduce the depth of IL at the start of the storm, but are only provided by the ARR Data Hub for storm durations of 60 minutes up to 72 hours, for events of 50% AEP through to 1% AEP.
Median Preburst Loss values can be downloaded from the ARR Data Hub using the Download TXT button at the bottom of the ARR Data Hub and then imported into DRAINS using the Rainfall Ensembles property sheet.
Note: failing to apply Preburst Depths could be over-estimating the available Initial Loss in the model
Note: NSW specific guidance on the Data Hub currently advises that if that Probability Neutral Burst Initial Loss values must be used instead Median Preburst Depths.
Note: VIC specific guidance on the Data Hub currently advises that if the site is located within Region 3 then the 75% Pre-burst Depths must be used instead Median Pre-burst Depths.
Example preburst depths are shown below:
Probability Neutral Burst Initial Loss & Transformational Preburst Depths (NSW Only)
For NSW Studies, the ARR Data Hub currently advises that Probability Neutral Burst Initial Loss (ILpnb) values must be used instead of Median Preburst Depths and Ratios.
The equation to calculate Probability Neutral Burst Initial Loss is similar to Equation 1 above for ILb except Transformational Preburst Depths are used instead of Median Preburst Depths.
Equ 2: Probability Neutral Burst Initial Loss (ILpnb) = Initial Loss Storm (ILs) - Transformational Preburst Depths
Similar to Median Preburst Depths the ARR Data Hub only provides data for storm durations of 60 minutes up to 72 hours, for events of 50% AEP through to 1% AEP. DRAINS continues to apply the 60 minute duration depths for durations less than 60 minutes as advised in Table 9.6.5 of ARR 2019 Chapter 6 Book 9.
Preburst Loss values can be imported into DRAINS using the Rainfall Ensembles property sheet.
Example Probability Neutral Burst Initial Loss depths & Transformational Preburst depths are shown below:
Climate Change Factors
Below are example Climate Change Factors obtained from the ARR Data Hub. These are the factors that relate to urban drainage calculations. Climate change adjustments can be made using a climate change rainfall multiplier in the Project Options property sheet of DRAINS.
You are now ready to transfer this data to your DRAINS Model via the Rainfall Ensembles property sheet.
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