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A model approach

The Environment Agency may have its hands full now but it has come a long way in the last two years, says Nina Lovelace.

The Environment Agency has had its work cut out recently. Employees have been working up to 20 hours a day to control the worst flooding the country has seen for 40 years.

Chief executive Geoff Mance estimates that the resulting damage will cost at least £12M to put right. Administrating repair work will itself notch up a £4M bill.

Amid the chaos it is easy to forget that since the 1998 Northampton floods the Agency has introduced flood warning systems that have helped mitigate the disaster. Yet there is still room for warning improvements, and a lot more to learn about the science of flooding.

And as regional flood warning engineer Paul Goodwill explains, computer databases and software can help.

To predict or model floods, the Agency needs accurate weather information, explains Goodwill. 'All our regional offices are linked to the Met Office by our Hyrad software.'

Developed by ecology and hydrology research centre CEH Wallingford, Hyrad offers real time weather patterns and forecasts together with historical weather data for a region. 'We can look at what weather is coming in, and estimate rainfall intensities over the following few hours. This can be used quantitatively in flood forecast models, ' says Goodwill.

Popular flood forecasting models include Isis, produced by a joint venture between Halcrow and HR Wallingford, and the Danish Hydraulic Institute's Mike 11.

'Isis is a general purpose river model, ' explains Rob Millington, engineering software sales manager for HR Wallingford. 'It is based on equations that relate to open channel flow, and the relationship of upstream and downstream water levels.'

A section of a river is modelled by first feeding topographic information from survey work into the software to produce a three dimensional digital map.

The model is then calibrated using historical weather and catchment data. This can be fed into the model manually, but the Agency often uses CEH Wallingford's Flood Estimation Handbook CD to input data directly into the Isis model. Finally, real time weather information from Hyrad is input, allowing the Agency to run real time models.

The model produces a series of hydrographs showing resulting flood waters moving down river. This time lapse sequence enables engineers to predictwhere along the river and when the worst floods can be expected. Cross referencing the flood model with data on adjacent civils structures makes it possible to predict effects on housing, highways, earthworks or urban drainage.

However, Goodwill notes: 'Once the water leaves the bank, we can only estimate where it will go based on historical information and floodplain maps.'

The Agency hopes to rectify this by spending over £3M on research for the southern region.

It aims to deliver a new forecasting system capable of predicting more exactly the extent and depth of floods in targetted areas. The new software will transfer forecast levels from models such as Isis onto more extensive digital terrain models to create maps of flood inundation.

'The next generation of flood modelling and forcasting software will cover a wider geographic flood risk area than at present and will make it possible to pinpoint precise locations, ' says Goodwill.

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