Tutorial 10 - PMP Estimation In Australia, the Probable Maximum Precipitation (PMP) storms are estimated using three generalised methods: Generalised Short Duration Method (GSDM) for short durations. Generalised Southeast Australia Method (GSAM) for longer durations used in southeast Australia. Generalized Tropical Storm Method (GTSMR) for longer durations used in parts of Australia affected by tropical storms. PMP is defined by the (WMO, 1986) as " Manual for Estimation of Probable Maximum Precipitation The greatest depth of precipitation for a given duration meteorologically possible for a given size storm area at a particular location at a particular time of the year, with no allowance made for long-term " climatic trends. Generalised Methods of estimating PMP use data from all available storms over a large region and include adjustments for moisture availability and differing topographic effects on rainfall depth. The adjusted storm data are enveloped by smoothing over a range of areas and durations. Generalised methods also provide design spatial and temporal patterns of PMP for the catchment. More detailed information can be found in the following . website The storms with return periods within 100 years and PMP are estimated using the method provided in ARR 1997 (Estimation of Large to Extreme Floods – Book Six, ARR 1997). This tutorial details the step by step procedure of estimating PMP using XPRafts for the GSAM Sample B catchment (refer to Guidebook to the estimation of PMP – GSAM, Bureau of Meteorology, 1997). The catchment is located in Northeast Victoria with a total area of 436 km . The catchment lies in the 2 GSAM inland application zone, and GSDM needs to be calculated since the area of the catchment is less than 1000 km² (refer to the following images from the Guidebook to the estimation of PMP – GSAM, Bureau of Meteorology). The Latitude and Longitude of the centroid of the catchment are: 36deg19’ S and 146deg36’E, respectively and it falls under Zone 2 for Australian Rainfall Temporal Pattern. In this tutorial, you will learn the following: In this tutorial, you will simulate the design rainfall events for 5, 20, and 100 years return period and PMP. The durations of the design storms are 15 min, 1 hr, 2 hr, and 1 day. It means that 4 events x 4 durations = 16 design storms will be simulated. While XPRafts can estimate the PMP values automatically, you need to specify the return period and duration.
Transcript
Tutorial 10 - PMP EstimationIn Australia, the Probable Maximum Precipitation (PMP) storms are estimated using three generalised methods:
Generalised Short Duration Method (GSDM) for short durations.Generalised Southeast Australia Method (GSAM) for longer durations used in southeast Australia.Generalized Tropical Storm Method (GTSMR) for longer durations used in parts of Australia affected by tropical storms.
PMP is defined by the (WMO, 1986) as " Manual for Estimation of Probable Maximum Precipitation The greatest depth of precipitation for a given duration meteorologically possible for a given size storm area at a particular location at a particular time of the year, with no allowance made for long-term
"climatic trends.
Generalised Methods of estimating PMP use data from all available storms over a large region and include adjustments for moisture availability and differing topographic effects on rainfall depth. The adjusted storm data are enveloped by smoothing over a range of areas and durations. Generalised methods also provide design spatial and temporal patterns of PMP for the catchment. More detailed information can be found in the following .website
The storms with return periods within 100 years and PMP are estimated using the method provided in ARR 1997 (Estimation of Large to Extreme Floods – Book Six, ARR 1997).
This tutorial details the step by step procedure of estimating PMP using XPRafts for the GSAM Sample B catchment (refer to Guidebook to the estimation of PMP – GSAM, Bureau of Meteorology, 1997). The catchment is located in Northeast Victoria with a total area of 436 km . The catchment lies in the 2
GSAM inland application zone, and GSDM needs to be calculated since the area of the catchment is less than 1000 km² (refer to the following images from the Guidebook to the estimation of PMP – GSAM, Bureau of Meteorology). The Latitude and Longitude of the centroid of the catchment are: 36deg19’S and 146deg36’E, respectively and it falls under Zone 2 for Australian Rainfall Temporal Pattern.
In this tutorial, you will learn the following:
In this tutorial, you will simulate the design rainfall events for 5, 20, and 100 years return period and PMP. The durations of the design storms are 15 min, 1 hr, 2 hr, and 1 day. It means that 4 events x 4 durations = 16 design storms will be simulated.
While XPRafts can estimate the PMP values automatically, you need to specify the return period and duration.
Generalised Method Zones for GSAM and GTSMR, (Source: The Estimation of Probable Maximum Precipitation in Australia: Generalised Southeast Australia Method – Bureau of Meteorology)
GSDM (Source: Guidebook to the Estimation of Probable Maximum Precipitation: Generalised Southeast Australia Method – Bureau of Meteorology)
Location of the catchment (Source: Google Earth)
The data/files supplied to complete this tutorial are:
File Name Type Description
Aerial_Image.jpg Image file Aerial image of the project area
Aerial_Image.jpw World coordinate file File associated with the image file
PMP.xpt XP Template file Contains temporal pattern for PMP, default job control settings, global databases, etc
Catchment_B_Extent.xpx XPX file Contains the extent of the catchment B
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Creating the File from Template
First, you need to create the file using the template.PMP.xpt
Open XPRafts Go to . Name the model and in your desired location.. File > New > Create from Template PMP.xp Save
Now XPRafts asks you to select the template in the Template folder in the installed directory by default. Choose the template named and PMP.xptthen click .Open
Loading Background Image and Catchment Extent
Add a new background image (follow procedure described in section ).Aerial_Image.jpg Tutorial 6 - Subdivision - Pre DevelopmentLoad the catchment extent called Go to , browse for the file and then click . In this example, Catchment_B_Extent.xpx. File > Import Data Openthe catchment has been made available for training purposes.
You can use *.shp, *.dwg, *.dxf, or image files to digitize the catchments.
The file contains the GSDM, GSAM, and GTSMR temporal patterns and the IFD data for the study area.PMP.xpt
3. You need to create the catchment if it is not available by using the tool . Alternatively, you can go to in the main Create Subcatchment PMPmenu, select , and then digitize the catchment. You need define the whole catchment, as well as sub-catchments as Catchment Extent > Createrepresented in the next section.
Creating Subcatchments
Digitize three sub-catchments, as shown in the following figure, using the tool. Alternatively, you can files as Create Subcatchment add *.shp, *.mif, *.dwgcatchment background images and digitize the catchments using the tool. Create Subcatchment
Creating Catchment Collection Points
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Add nodes in the catchments outlet points using the tool , then connect these nodes (from ) using the tool .Node Node 1 to Node 3 Link
Now, you need to connect the catchments to the outlet nodes. Make sure that the tool is switched-off when Lock Catchments
connecting the catchments to the collection points. Select the tool and click the catchment. The cursor changes as shown in the Pointerimage below. Keep the left button pressed and release it when the cursor reaches the outlet node. Select the Drain Catchment As > Subcatchment1.
Repeat this step for all the other catchments.
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3. Select all the nodes by clicking the tool . Go to menu, select and then click .Select all nodes Tools Calculate Node Catchment Area
The catchment areas are then calculated and assigned as to the nodes.FIRST Subcatchment
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Click and return to the main network window.OKDouble-click any node to open the dialog and select . Click the button. You can Node Control Data Subcatchment Data FIRST Subcatchmentsee that the calculated area is assigned in to the node.Total Area
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Double-click to open the dialog and enter as . Similarly, enter the for as . Click after you link 1 Link Lagging LAG 200 min LAG link 2 350 min OKhave finished.
Now, add a loss model to the subcatchments. Go to and highlight . Configuration > Global Data Init./Cont. Losses
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Click and enter the name as New NoInfil.
Click and enter the values of for both and .Edit 0 Initial Loss Continuing Loss of Absolute
Click to return to the main network window.OK
Setting up Spatial Distribution for Short Duration PMP
GSDM Ellipses are used to establish the spatial distribution of PMPs for shorter durations.
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Go to in the menu bar, select .PMP GSDM Ellipses > Show Ellipses
You can see the 10 ellipses on the screen now (A – J) and the center point of the ellipses as a small circle.
The next step is to overlay the ellipses with the catchment outline by moving and rotating to obtain the best fit by the smallest possible ellipse. To do this, click the Center Circle of the ellipses and hold left mouse. Now, you are able to move the ellipses. To rotate the ellipses, press Shift on the key board.
While moving and rotating the ellipses, you are able to see the dialog which shows the GSDM spatial distribution calculations. To PMP Monitorsee this monitor, click in the menu bar, select .PMP GSDM Ellipses > Show PMP CalculationsGo to and then select You can see that the ellipses are locked and cannot be moved.PMP > GSDM Ellipses Lock Ellipses.
You can lock the nodes and catchments as well using the and tools respectively.Lock Node Positions Lock Catchment
Using the Automated Storm Generator
Automatic Storm Generator is used for generating storms with any storm durations and any return periods. Storms up to 100 years return period is estimated using the IFD coefficients, rainfall duration, and temporal pattern depending upon the zone (AR&R, 1987).
To activate the Automatic Storm Generator, go to . Alternatively, click the icon and select Configuration > Job Control Job Control Job .Definition
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Click the radio button.ARR87 Automatic Storm Generator
Now you can see the dialog. Click the tab.Global Storm Generator Global Storms
Click and select the global database for IFD coefficients called . The Albury data is included in the template file and IFD Albury PMP.xptrepresents the IFD coefficients for the region.
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Click and you can see the IFD coefficients for the project area.Edit
Click . Select and click in the dialog box.OK Albury Select
In the dialog, enter the Zone as 2, as the study area is under zone 2 of the Australian rainfall temporal pattern. Refer to Global Storm Generatorthe following figure given by ARR 1987:
You can get the IFD coefficients from the ARR 1987, Volume 2. Design rainfall isopleths’ maps are available for 2 and 50 years for 1, 12, and 72 hours durations. Location skewness and geographical factors are also available in the ARR volume. Otherwise, you can get these coefficients from the Australian Bureau of Meteorology .website
Design Rainfall Temporal Pattern Zones for Australia (Source: ARR 1987, BOM)
In the dialog, under , enter as Under enter Global Storm Generator Time Control Routing Increment 1 min. Simulation Time Simulation Time
.= Storm Duration x 1
Under select Storm Duration 15, 60, 120, and 1440 min.
Under select and then click .Return Period 5, 20, 100, and PMP OK
Now XPRafts calculates 4 events x 4 durations = 16 design storms chosen for the catchment. The temporal patterns up to 100 year return period are stored in the program. The engine picks up the corresponding temporal pattern for a storm depending upon the zone, return period, and duration. However, you should specify the temporal patterns for the PMP. For GSDM, there is a single temporal pattern (up to 3 or 6 hours).
When you select PMP as return period, 10, 20, 25 min Storm Durations will be greyed out automatically as PMPs will not be calculated for these durations.
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Temporal Pattern for PMP for short durations (Source: the Estimation of Probable Maximum Precipitation in Australia: Generalised Short-Duration
Method, BOM, 2003)
There are different temporal patterns for GSAM and GTSMR depending on the catchment area and storm duration. The temporal pattern for GSAM and GTSMR starts at 24 hours. You should estimate the in-between values (3-24 hours) as described in the GSAM and GSTMR Guidebooks from Bureau of Meteorology.
Setting up GSDM Data for Shorter Duration Storms
Go to in the main menu and open Configuration Job Control.Click and then select the tab. Automatic Storm GeneratorARR87 PMPYou can see that the of the catchment is automatically calculated. Now enter of and of for the Total Area Latitude -36 19’ Longitude 146 36’catchment centroid. These values will be used in calculation of adjustment factors for and/or Enter of GSAM GTSMR. PMP Return Period 10000
.00 years
Under , select as from the drop down list. GSDM - Generalized Short Duration Method Duration Limit < 3 hrClick and select from the global database imported from the file, and then click Temporal Pattern GSDM PMP.xpt Select.
The data will be used to interpolate values between 100 years and PMP (for example, 150 or 200 year return period).
There is only one temporal pattern for the short duration PMP estimation that is GSDM.
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6. Click to open for GSDM and enter the following values:GSDM Worksheet Global Storms Summary
(smooth fraction of terrain) as Smooth (S) 0
as EAF 1
as MAF 0.60
Refer to the Estimation of Probable Maximum Precipitation in Australia: Generalised Short-Duration Method (BOM, 2003) for more details about terrain types and adjustment factors. The paragraph below is cited in the guidebook:
“Rainfall from single, short duration thunderstorm events is not significantly affected by the terrain. Therefore, it is not necessary to classify the terrain of the catchment for durations of an hour or less. If durations longer than one hour are required, the next step is to establish the terrain category of the catchment and to calculate the percentages of the catchment that are ‘rough’ and ‘smooth’. ‘Rough’ terrain is classified as that in which elevation changes of 50 m or more within horizontal distances of 400 m are common. ‘Rough’ terrain induces areas of low level convergence which can contribute to the development and redevelopment of storms, thereby increasing rainfall in the area over longer durations. Terrain that is within 20 km of generally ‘rough’ terrain should also be classified as ‘rough’. If there is ‘smooth’ terrain within the catchment that is further than 20 km from generally ‘rough’ terrain, an areally weighted factor of ‘rough’ (R) and ‘smooth’ (S) terrain should be calculated such that R plus S equals one. If a catchment proves difficult to classify under these guidelines then the whole catchment should be classified as ‘rough.’
“The mean elevation of the catchment should be estimated from a topographic map. If this value is less than or equal to 1500 m the EAF is equal to one. For elevations exceeding 1500 m the EAF should be reduced by 0.05 for every 300 m by which the mean catchment elevation exceeds 1500 m. For most catchments in Australia the EAF will be equal to one.”
Click under the tab in the dialog. You see that the GSDM PMP depths are estimated from Equation (in Update GSDM Global Storms Summary the table) up to 3 hours as you specify the duration limit to PMP Values (mm) < 3 hrs.
The in the table for the Smooth Terrain calculated are .Initial Depth Smooth (Ds) PMP Values (mm) 0
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8. Click in the dialog. OK Global Storms Summary
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Go to in the dialog. Select and click . This is now applying Apply Spatial Factors Global Storm Generator Compute for All Durations OKspatial variation to sub-catchments based on their coverage of the GSDM ellipses.
Setting up GSAM Data for Longer Duration PMP
Go to in the main menu and open Configuration Job Control.Click and then select the tab. ARR87 Automatic Storm Generator PMPUnder , select Long Duration PMP Method GSAM.
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In , select from the drop down list. GSAM Zone Inland
Now, you need to specify the for the 24 hours Select as the temporal pattern (that is, Temporal Pattern GSAM PMP Storm. GSAM_I500_24 GSA
). Click .M, Inland, 500 km2, 24h hours Select
You do not need to specify the temporal pattern for PMP storms as they fall under short durations, hence the 15, 60, and 120 minGSDM temporal pattern will be applied.
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Click and select the tab.Global Storms Summary GSAMUnder click under and TAF will be calculated based on the entered CATCHMENT FACTORS, Compute Topographic Adjustment Factor (TAF)latitude and longitude.Similarly, click under to calculate for and Alternatively, you can directly enter Compute EPW Seasonal catchment average Summer Autumn.the values of TAF and EPW.
Click in the dialog and you can now see that are calculated.Update Global Storms FINAL GSAM PMP ESTIMATES
Setting up the GTSMR Data for Longer Duration PMP
For Catchment B, the GTSMR estimation is not required. However, for some other catchments GTSMR estimation will be required based on the location. You can follow the same procedure that is provided for the GSAM. For some catchments, both GSAM and GTSMR will be applicable, for example, GSAM-GTSMR Coastal Transition Zone. In this case, the PMP depths should be estimated by both methods and the maximum value is selected.
Analysing the Results
XPRafts calculates the TAF and EPWs values based on the latitude and longitude of the catchment centroid. It will be more accurate if the average value for the catchment is calculated by overlaying the catchment outline on the TAF and EPWs grids as described in the GSAM Guidebook.
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Click to simulate the model.SolveTo review results, select the nodes that you wish to see the results and click . Review Results
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