A New Flood Inundation
Modelling
Gareth Pender
School of Built Environment
Heriot Watt University
Contents
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Introduction to rapid flood spreading modellingprediction of flood depth and flood extent.
A new conceptual model for maximum velocity
prediction.
IIIustration of application to an artificial digital
elevation model.
IIIustration of application to case studies.
1.1 Existing RFSMs
RFSMs
Heriot Watt University
Halcrow
HR Wallingford
Martin Krupka and Yang Liu.
ISIS Fast.
Julien Lhomme et al.
(1) Krupka M., Wallis S., Pender S., Neélz S., 2007, Some practical aspects of flood inundation modelling, Transport phenomena
in hydraulics, Publications of the Institute of Geophysics, Polish Academy of Sciences, E-7 (401), 129-135.
(2) Lhomme J., Sayers P., Gouldby B., Samuels P., Wills M., Mulet-Marti J., 2008, Recent development and application of a rapid
flood spreading model, River Flow 2008, September.
(3) Liu Y, Pender G (2010) “A new rapid flood inundation model”, the first IAHR European Congress, Edinburgh, UK.
1.2: Requirements for an RFSM
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Short time to run (Typically < 5s)
A good overall agreement of the final water depth and
flood extent predictions between SWEM and RFSM.
A good overall agreement of the maximum velocity
prediction over a flood cell between SWEM and RFSM.
useful for application to catchment scale flood modelling
and probabilistic flood risk analysis (e.g. Bayesian
Analysis).
1.3 Basic RFSM algorithm
RFSM
flood cells
DTM grid
cells
Pre-calculation
An array of flood storage cells is constructed from DEM

Inundation
A specified volume of flood water is distributed across the storage cells.

Real
Floodplain
Minimum
Cell Plan
area (Amin)
Minimum
Depth
(Dmin)
An example of pre-calculation process
Volume (cubm)
Water level (m)
An example of constant extra head (source: Krupka et al. 2007)
1.4 Two different spreading algorithms
Next active grid
Current active grid
(a)
One-directional RFSM
(b)
Multi-directional RFSM
1.5 Our improved RFSM

(1)
(2)
(3)
Rules to provide accurate prediction:
Water will spread from high location to lower locations (one directional
or multiple directional spilling algorithms) with merging process.
Dynamic Driving head based on inflow hydrograph
Floodplain area with a high roughness uses a high driving head
Area 2
discharge
Area 1 =
Area2
t
Fig. Inflow Hydrograph
1.6 Model parameters and evaluation functions
(1)
(2)
(3)
1.7 Application example
Inflow
hydrograph
Inflow
3D plot
1.8 Compare RFSMs with ISIS2D
Flood extent using ISIS2D
after 10 hours
Flood extent using MD-RFSM
Flood extent using OD-RFSM
Water depth of cross section comparison using ISIS2D and RFSMs
1.9 ISIS2D simulation
10 m grid resolution ISIS2D model will take about 1 hour to run.
1.10 One directional RFSM spilling process
RFSM will take about 1 second to run.
2.1 Maximum Velocity prediction using a new
conceptual model
Volume = vol
Inflow at time
Area of a big
flood cell
outflow at time
2.2 Performance Comparison of the conceptual
model and ISIS2D
Maximum velocity using
ISIS2D
Average Maximum velocity
for 17 regions using ISIS2D
Average Maximum velocity
predictions for 17 regions
using our proposed model
The conceptual model parameter C was calibrated using one
ISIS2D simulation with peak inflow value= 150cubm/s for
inflow hydrograph.
2.3 Performance statistics
2.4 Application to Thamesmead, London
Thamesmead 2m resolution grid digital elevation data and
inflow hydrograph.
2.5 Performance Comparison of the conceptual model and TUFLOW
(a): Final water depth after 1hour using RFSM
(c): Region average maximum velocity prediction using the new conceptual model
(b) : Final water depth after 1hour using TUFLOW
(d): Region average maximum velocity prediction using TUFLOW
2.6 Current work about 2005 Carlisle flood event
2.7 Flood extent predictions Using ISIS2D and
RFSM
Fig.2. Flood extent and water depth at 45.25 hours using RFSM.
( 5m grid resolution model will take 2 seconds to run)
Fig1. Flood extent and water depth after 45.25 hours using ISIS2D.
(15m grid resolution model will take more than 1 hour to run)
2.8 Performance statistics
Future work
(1) Test more locations.
(2) Fast Rapid flood spreading Modelling using
Cellular Automata.
Thank you!