Evaluating 2D Models to Aid Flood Prediction
Prof. Garry Pender
The Challenge
In order to prepare for, and, reduce the risk from flooding, the Environment Agency uses a
number of modelling tools in decision-support for Flood Risk Management practices. It is
generally accepted that most practical problems of floodplain inundation, where horizontal
length scales typically exceed flood depths by several orders of magnitude, are best
described in two-dimensions (2D); hence a proliferation of 2D hydraulic models exist.
Understanding the relative merits (and deficiencies) of individual approaches is, however,
limited and requires examination of both, the model codes and, their sensitivity to
calibration if model output is to be correctly interpreted.
Our Approach
Benchmark testing of six 2D hydraulic models was undertaken (DIVAST, DIVAST-TVD, JFLOW,
LISFLOOD-FP TRENT and TUFLOW) for the July 30th 2002 inundation event of a densely
urbanized area of Glasgow. Models’ abilities to simulate surface flows were rigorously
compared and contrasted, highlighting three generic outcomes: (i) Terrain data available
from modern LiDAR systems are sufficiently accurate and resolved for simulating urban
inundation. Yet, this needs to be fused with digital map data of building typology and land
use to gain maximum benefit from the information contained; (ii) High degree of sensitivity
to calibration of the friction parameter calibration; hence, single deterministic simulations
should be avoided in preference of a range of plausible friction parameters or additional
observational data; (iii) No assumptions should be made regarding the class of code (e.g.
storage cell; full shallow-water) and its computational expense. The intention was to provide
evidence that 2D hydraulic modelling packages used for flood risk management, by the
Environment Agency and their consultants, are capable of adequately predicting the
variables upon which flood risk management decisions are based.
Since publication of these benchmarking tests on Glasgow (Water Management, 161 p. 1330; 2008), a more comprehensive study has been delivered and reported via “Delivering
Benefits Through Evidence” (Environmental Agency, pp. 161; 2010). This document
benchmarks a wider range of 2D modelling software and a greater diversity of flood flow
scenarios (e.g. dam break; filling of floodplain depression; surcharging sewers etc.).
Benefits from the Research
Since publication of these benchmarking tests on Glasgow (Water Management, 161 p. 1330; 2008), a more comprehensive study has been delivered and reported via “Delivering
Benefits Through Evidence” (Environmental Agency, pp. 161; 2010). This document
benchmarks a wider range of 2D modelling software and a greater diversity of flood flow
scenarios (e.g. dam break; filling of floodplain depression; surcharging sewers etc.). Crucially,
this work underpins the Environment Agency’s decision-making in Flood Risk Management
in England and commercial model developers have been provided with a transparent
framework with which to test new models.
Future Work
“Delivering Benefits Through Evidence” (Environmental Agency, pp. 161; 2010) clearly notes
two areas for development: (i) continual review of suitability of benchmark tests to account
for new science and modelling trends; (ii) detailed research into model linking (e.g.
combined 1D/2D approaches) in terms of the choice of models, run times and consistency in
model prediction.
More Information
This project was supported by EPSRC, NERC and the Environment Agency. Further
information on this project can be found at

http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CC4
QFjAA&url=http%3A%2F%2Fevidence.environmentagency.gov.uk%2FFCERM%2FLibraries%2FFCERM_Project_Documents%2FSC120002
_Benchmarking_2D_hydraulic_models_Report.sflb.ashx&ei=9H18U8XiKeqc0QWh9ID
YBQ&usg=AFQjCNFK85nEAZ5r4nC7tOnALM5c_6Jsag&bvm=bv.67229260,d.d2k&cad
=rja

http://web.sbe.hw.ac.uk/frmrc/downloads/fact_sheets/FRMRC2%20Fact%20Sheet%2015%20v01%20newformat.pdf