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Modelling outputs displayed using ISIS MAPPER

The Flood Modeller 1D solver was used by BRL Ingénierie, a consulting firm offering specialised services in the areas related to water, the environment and regional land-use management, to model the potential flood risk of the River Têt and its tributaries in order to develop a flood risk management plan. The study modelled approximately 25 kilometers of river covering an area of 45 square kilometers.

The development of the 1D model required bathymetric cross-section data for the river channel, a digital elevation model (DEM) for the floodplain and a survey of the bridges, weirs and other structures along the river reach.

The river channel network was represented by a set of one-dimensional (1D) models. Where required, 400 points can be used to represent a cross-section and the user can vary roughness coefficients around the cross section to represent zones of different roughness.

The bridges, weirs and orifices were modelled using the geometric data of the hydraulic structures. The software calculated the energy loss using the appropriate hydraulic equations.

The floodplain was modelled using flood cell (or ‘reservoir’) units with each unit defined by a surface area versus elevation relationship. Spill units were used to form the link between the 1D channel nodes and the floodplain. The main data used within the spill units were sets of offset/elevation pairs describing the irregular profile of the bank tops.

The BRL Ingénierie in-house bespoke software (OASIS) was used to build the model, as it was integrated with ArcGIS and allowed the automatic construction of floodplain models. The mapping interface in our software could also be used to help build the model.

The results of the modelling consisted of a water depth map, a velocity map and a flood risk map, all of which could be viewed in our software.

Fabrice Cebron of BRL Ingénierie commented that our 1D solver "was chosen because it's one of the oldest, most robust 1D hydrodynamic simulators available and is very easy to use," and that having used our software since 1999, BRL Ingénierie "know how to efficiently use the system to produce high quality results".

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