Environmental Engineering Reference
In-Depth Information
to 36 hours ahead. The Environment Agency's
flood forecasting system for the Thames Estuary
consists of a ProudmanOceanographic Laboratory
2D model of the North Sea and eastern English
Channel linked at Southend to an ISIS 1Dmodel of
the Estuary. The 1D forecasting model runs both
as part of the Agency's National Flood Forecasting
System and as part of Themis. Themis is a soft-
ware system developed for the Agency for real-
time flood simulation including the production of
real-time flood maps (Fig. 23.5).
approaches using fully linked models were con-
sidered but were rejected as they would not have
achieved the Flood Map specification and may
have led to underestimates of risk.
A sensitivity analysis was undertaken using
variations in ground data (LiDAR, synthetic aper-
ture radar (SAR)), roughness coefficient (base, n
¼ 0.050), boundarywater level (base, base þ 0.3m,
base 0.3m) andmodel grid size (5m, 10m, 20m).
The analysis suggested that results are most sen-
sitive to ground data and model grid size. For
defining Flood Zones, a grid size of 10m derived
from LiDAR was found to be optimum in terms of
balancing run times and resolution of results.
The Themis system
The Themis software was developed to automat-
ically link with existing Agency systems to re-
ceive the latest predictions of Teddington fluvial
flows and Southend tides/surges. The software
allows users to manually adjust boundary data
and add potential/actual defence breach locations
before undertaking 2D and/or 1D simulations.
Operation of the Thames Barrier can also be
Flood Forecasting
Introduction
Flood forecasting models need to run quickly and
robustly to provide sufficiently accurate predic-
tions of water levels at key 'action' thresholds up
Fig. 23.5 Predicted flooding following a hypothetical breach at Enderby'sWharf. (See the colour version of the figure in
colour plate section.)
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