Tips and Tricks for Flood Modelling with Confidence

Tips and Tricks for Flood
Modelling with Confidence
By Gavin Fields
Senior Water Resources Engineer
XP-LIVE webinar
∼ This is part of our XP-LIVE educational program
∼ Webinars have been recorded and are available at
http://www.xpsolutions.com/category/news/xplive/
∼ The session addresses:
∼ Model Setup
∼ Hydrology
∼ Hydraulics
∼ Modeling and Results
∼ Some typical models are shown to demonstrate the above
items
∼ Question/Answer
Model Setup
∼ Data input is the most important element to any numerical
model
∼ Therefore template files (from XP Solutions or user defined)
allow efficient model setup
∼ e.g. MASTER2006_Metric.xpt
∼ A key part of template file should
include a well defined XPTable
∼ XPTables are a modeler's ‘best friend’
Model Setup - XPTables
∼ XPTables from the ‘master’ templates include the table
definition of the output files
∼ Data can be copied and pasted from within the table and from
external databases, such as Excel
∼ Custom Variables can also be created within XPTables, which
can be equations defined by the user
Model Setup - XPTables
∼ XPTables also link to Quick Data View to show parameters for
individual elements in the network view.
∼ Quick Data View also shows the header values for GIS files
linked to the model
Model Setup – Job Control
∼ Job Control is one of the initial points of review undertaken by XP
Solutions when models are submitted via our Support Portal
(http://support.xpsolutions.com)
∼ Time Control, within the Job Control, for the RNF and HDR modes is a
critical element that must start at the same time. This is particularly
crucial for temporal patterns that may be applied
Model Setup – Job Control
∼ 2D Job Control is separate to the HDR Job Control and is
available to users with the XP2D add-on to xpswmm and xpstorm
∼ The recommendation for 2D time step is to no greater than
half of the 2D grid dimension (i.e. 2.5 seconds for a 5m grid)
∼ Default land use will designate the surface roughness and loss
relationship (if required) within the 2D domain
∼ Double-precision is required for ‘Direct Rainfall’ models
Model Setup – Job Control
∼ The currently recommended Smagorinsky viscosity values are:
∼ Smagorinsky Coefficient = 0.5
∼ Constant Coefficient = 0.05
∼ The above values have changed over the last few years and
users should review this aspect – particularly for ‘old’ models
Model Setup – Job Control
∼ Model output defines the regularity of 2D results that can be
reviewed by the user. The interval can be as long or as short
as is required for the interpretation of the output
∼ For users who wish to model Time-to-Inundation, specific
levels can be defined for reporting purposes (i.e. 0.15m for
top of kerb, 0.25m for trafficability etc.
Model Setup – Job Control
∼ Initial water levels can be applied to the 2D domain – and should be
adjusted in the event you have ‘dry’ terrain below an elevation of 0m
∼ It is common for the 2D Cell Checks to ‘adjust’ the levels by adopting the
1D element data (i.e. node invert or spill crest elevations). User must
apply caution for this arrangement based on the grid size as some
elements can be ‘lost’
Model Setup – Job Control
∼ Advanced settings are available, but should generally be used with
CAUTION.
∼ For users with a current maintenance agreement and using the current
version of the software we do not recommend using the previous 2D
calculations.
∼ For users who desire DAT file output for post-processing then either
option in the dialog below may be desirable
Model Setup – Configuration
Parameters
∼ Configuration parameters are available to modify the default
behaviour of the model engine. Common parameters include:
∼ CATSLOPE=% (converts the slope parameter to % instead of
∼
∼
∼
m/m)
ZREF=? (where ? is any elevation. This parameter sets the initial
water level in all 1D elements)
MINLEN=? (where ? is any length in metres. Reduces the warning
reference for default minimum link length)
SHOW_CONTINUITY (displays the continuity summary at
completion of model run)
Model Setup – Configuration
Parameters
Model Setup – DTM
∼ Topographic data can be used to assist the development of 1D
models and is critical for 1D/2D models.
∼ Users need to understand the limitations of the data applied
within the program and should review it for erroneous
triangles that may occur at the ‘boundaries’ or at ‘null’ areas
∼ Users can dynamically review ‘z’ values via the status bar
Hydrology – Data Input
∼ Users can use the catchment tool to detail catchment
polygons, link to specific nodes and then calculate the areas
(Tools\Calculate Node\Catchment Areas)
Hydrology – Data Input
∼ If splitting catchment for Laurenson’s Method, catchment
areas can be applied to sub-catchment 5 to then split using
custom variables, based on the design fraction impervious, in
XPTables
∼ In this way, the sum of catchments 1 and 2 must equal
catchment 5
Model Setup - XPTables
Hydrology – Data Input
∼ When developing a model users can, and should, use
XPTables as the primary input and review tool prior to solving
a model
∼ Points to check include:
∼ Consistent hydrologic method (i.e. Laurenson, Time Area, etc.)
∼ Loss model input data (e.g. Uniform Loss, Horton or Green Ampt)
∼ Slope and width parameters are appropriate (using engineering
judgement). Note: Laurenson’s Method does not use width.
∼ For Laurenson’s Method ensure that catchments are split into
pervious and impervious components
∼ For Rational Method review the method used to determine
the Time of Concentration.
Hydrology – Data Input
Inappropriate
Hydraulics – Data Input
∼ xpswmm/xpstorm are stormwater infrastructure models, as a result small
diameters should be avoided (i.e. >0.05m - the default minimum).
∼ The default minimum link length is 10m, but can be reduced in
conjunction with configuration parameter MINLEN. This length can occur
in designs, but should be looked for prior to solving as it may mean a link
has not been updated with real data
∼ XPTables can be used to review both of these items
Hydraulics – Data Input
∼ Dynamic longitudinal sections can confirm that the network is
properly graded.
∼ Note: XPTable data can be turned off from the view
Hydraulics – Data Input
∼ Node Ponding is another important element to be reviewed
prior to solving any model.
Results
∼ Once your model has been solved results should be
thoroughly reviewed
∼ Model continuity and errors can be reviewed in the output
files via the Analyze menu
Results – 1D
∼ Dynamic longitudinal sections provide a graphical method to
review your model
∼ This view assists users to quickly identify 1d ‘flooding’
Results – 2D
∼ The 2D summary (Analyze\2D Simulation Summary) is an
initial reference point to review the performance of your 2D
model
∼ Cumulative mass errors
and flow results can be
reviewed via the drop
down icon
Results – 2D
∼ Plan results in 2D can be reviewed directly in the network view. Users can
also restrict model results display to highlight points of potential conflict
(i.e. high velocity requires scour protection, depth >0.3 untrafficable etc.)
Results – 2D
∼ Time Series Outputs (Flow Lines / Head-Velocity Points) can be used to
extract cumulated results from the 2D output
Results – 2D
∼ For models that require detailed review, users can produce the detailed
Check Files via the 2D Job Control, which can detail:
∼ Boundary Conditions;
∼ Grid details;
∼ 1D modifications to the
terrain model.
∼ We strongly recommend
users review the Help file
for further detail on the
model Check Files
Tips and Tricks for Flood Modelling with
Confidence
This has been an XP Solutions Presentation
by Gavin Fields
Senior Water Resources Engineer
Contact XP Solutions:
North America: 1-888-554-5022
Australia Asia Pacific: +61 (7) 3310 2302
United Kingdom: +44 0 1635 582555
[email protected]
Music for this video provided by Templates Wise at http://www.templateswise.com/

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