Advanced Hydrology 2018



During this educational webinar we dive into Australia’s favourite hydrologic method and take a look at the more advanced parameters.

  • See an overview of the new ARR 2016 & BOM data
  • Understand how Aerial Reduction Factors & Spatial Varying Rainfall can affect your project
  • Preview the soon to be released xprafts 2018.1 all new features
  • Learn how to link your hydrology results directly to your hydraulic model



Q & A’s – Advanced Hydrology 2018

Q: How do we decide how many time steps to smooth pre-burst depth over?
A: Determining pre-burst duration is an interim measure while we wait for the full storm temporal patterns.  The pre-burst should be spread over sufficient time to ensure the burst storm is not dwarfed by the pre-burst. I.e. The pre-burst should not cause the peak runoff.  If however, the pre-burst is small compared with the initial loss in the area, 1 timestep should suffice.

Q: How do you apply different IFD’s to different sub catchments?
A: Each sub-catchment has a ‘Location’ field that can be populated to match the ARR16 design rainfall (if using spatially varying).

Q: Any document about area reduction factor?
A: Refer to ARR 2016 Guidelines, Book 2 – Chapter 4

Q: Should we be selecting the median or mean pattern result?
A: The latest update is to use the MEAN.  This is consistent with the ARR 2016 guidelines text.  

Q: Is there a way to convert LOC and TOT files outside of the InfoWorks / XPSWMM environment?
A: The conversion of LOC and TOC into ICM is an interim measure while we investigate the best way to embed RAFTS method into ICM.  

Q: Is the export file compatible with other software (such as 12d?) Are there any collaboration between RAFTS/12d with the new ARR16?
A: We would recommend using XPSWMM / XPSTORM to integrate with 12d for ARR16.  They have a very good relationship and data plus, results can be moved back and forth easily.

Q: How do you recommend we represent equivalent impervious areas in split sub catchments?
A: Very good question! The equivalent impervious areas method is generally used for catchments with calibration data.  We would still recommend splitting the catchment into impervious and pervious and then adjusting the losses and roughness to suit.

Q: Does RAFTS allow importing a shapefile catchment and extract spatial varying IFD into it directly?
A: This is certainly something we would like to incorporate in future. 

Q: Do you think moving forward we should concentrate on InfoWorks and not XPSWMM?
A: We would recommend moving to InfoWorks ICM if working in a large team or on large flood projects.  XPSWMM is still the best product for small drainage design and basin sizing.

Q: Can anyone get a demo version of new XPRAFTS like the previous?
A: We would be happy to provide a personal demonstration of XPRAFTS 2018.1 at your convenience.

Q: Can I simulate routing links in XPRAFTS 2018.1?
A: Yes, the model shown in the demonstration was built using lag links, but all previous options for link routing have been retained.

Q: What is the reason for use of 63.2% AEP?
A: The 63.2% AEP refers to the 1yr ARI. Typically used for design of bank full flows and for assessing environmental impacts such as scour.

Q: If we utilise ilsax (moment area theorem), would this work instead of the laurenson method?
A: ILSAX is a linear method meaning a doubling of rainfall results in a doubling of runoff.  Studies have shown that most catchments (especially large rural) have a non-linear response to changes in rainfall meaning a doubling of rainfall would not result in a doubling of runoff.  

Q: Does this mean, this method would not be applicable in NSW?
A: XPRAFTS is suitable for use in all states of Australia.

Q: What is the difference between the inbuilt RAFTS function from DRAINS and XPRAFTS model?
A: We were not involved in the RAFTS function from DRAINS so, are unable to comment on the differences to the RAFTS method developed by Allan Goyen.

Q: Can I use discharge calculated from Drains at U/S boundary?
A: Yes, InfoWorks ICM can use upstream boundaries from any hydrologic package.

Q: How is the spatial variation calculated? Is it just averaged or is a Thiessen weighting type method used?
A: The spatially varying function just allows multiple design rainfalls to be used, downloaded and included in the one model. The design rainfalls are named and applied directly to the nodes with that location name.

Q: Does XPRAFTS 2016 have features compatible with ARR2016 hydrology calculation?
A: No, XPRAFTS 2016.1 was released prior to the Guidelines and therefore does not include the design rainfall.  The hydrologic routing calculations are however, unchanged.

Q: Is there an updated manual for XPRAFTS 2018.1 being prepared, or training opportunities for using ARR2016?
A: Check our training dates on our website for XPRAFTS 2018.1 training closest to you:

Q: Why is there a difference in peak flow using the hydrology in XPRAFTS compared to XPSWMM?
A: There are small differences in the convergence criteria between the Laurenson’s method implementation in xpswmm and xprafts, with xpswmm having a higher max number of iterations to achieve convergence. This can lead to small differences between xpswmm and xprafts, but they should be in agreement for most levels of tolerance.

Q: Can we still identify the critical channel flow depths and velocities within XP Table?
A: Yes, this functionality has remained the same.

Q: Does splitting the catchments not effectively assume two directly connected catchments rather than allow the likely longer time of concentration from a catchment with impervious amongst pervious?
A: XPRAFTS allows the modeller to construct hydrology models with both split or unsplit catchments. Research has found better calibration for a number of catchments with split models, however if the user believes that a combined catchment gives better results for their scenario that is possible within the XPRAFTS program.

Upcoming Training

Hydrology for Flood Risk Management
Brisbane, Australia
Nov 27, 2018

Introduction to InfoWorks ICM SE (Sewer Edition)
Melbourne, Australia
Nov 27-28, 2018

Canceled Event/Class
Melbourne, Australia
Nov 28-29, 2018

Canceled Event/Class
Howbery Park, UK
Nov 28-29, 2018

MicroDrainage: Two Day Introduction
Howbery Park, UK
Dec 4-5, 2018

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