The Communauté d’Agglomération de Pointe à Pitre (CAP) territory is very prone to flooding, particularly in urban areas. The flooding events can be sudden and extremely violent. DHI has developed a flood alert system that contributes to timely decision making that can mitigate flood impacts.

Challenge

Localised flash floods
The CAP territory is subjected to different kinds of floods: coastal flooding, river flooding as well as overflowing of water networks. The sudden floods of May 2012 in several sections of Pointe à Pitre, more specifically in Les Abymes and in Gosier, were a reminder of the specific risks of floods in urban areas. Due to localised storms, the area suffered 313 mm of rainfall in only a few hours, equivalent to three months of rain at that time of year in the region. This sudden and high intensity rainfall caused a rapid rise of floodwaters in the city, with a water depth reaching 1.5 m to 1.8 m.

Results showing overflows (red dots) and the insufficient capacities of the network during heavy rains (red lines) in a 10-year return period. © DHI

Urban floods in the CAP territory have various origins: runoff and collection of rainwater at the lowest point on road networks which are not connected to the storm drainage system, saturation or overflow of the storm drainage system. The rainwater sanitation master plan has revealed a network congestion during frequent heavy rainfall events which cause overflows on sections of Pointe à Pitre and Les Abymes occurred.

Localisation of flooding points and resource mobilisation are strategic organisational issues for CAP Excellence. The alert system developed by DHI has helped resolve these issues and increased the community’s efficiency in managing floods.

Solution

Early alert system for real-time flood forecasting
The forecasting and alert system set up by CAP Excellence covers the municipalities of Pointe à Pitre and Les Abymes in MIKE OPERATIONS.

The MIKE OPERATIONS forecasting platform integrates the MIKE URBAN modelling technology to model the storm drainage systems. The modelling of the hydrological response, which is the rainfall runoff transformation on river catchments, and the flow propagation in the network are thus integrated into the operating system.

With the MIKE OPERATIONS software, rainfall information is automatically collected and a simulation is launched each day. This system enables the user to predict the risks of the storm drainage system overflowing, and consequently, the risks of floods over a 24-hour period. The information is then transmitted to operators.

Modelling system
Knowledge about hydraulic operations is provided by MIKE URBAN. Characteristics of the system include:

  • 342 river catchments representing a total of 7,000 ha.
  • 2513 manholes
  • 2575 pipes
  • 1 rainfall station
  • 33 sea outfalls
Full autonomy of the system
The real-time forecasting management system created by the MIKE OPERATIONS platform is completely autonomous. This cuts manpower cost by eliminating manpower required to operate and manage the system. The forecasting system runs on its own where tasks are scheduled to be performed daily.
Scheduled tasks include:
  • Observed rainfall data gathering
  • Retrieval of rainwater forecast after a 24-hour period
  • Data processing
  • Data verification and validation
  • Running simulations
  • Results analysis
  • Alert notifications

Tasks are executed and results are obtained at 8 AM daily upon arrival of the CAP Excellence staff. The system uses weather forecast data provided daily by MeteoGroup, with hourly rainfall predictions over a 24-hour period.

Project value
Flood management and employment of flood mitigation strategies is very important in dealing with extreme weather emergencies. Using our MIKE OPERATIONS software, we are able to provide CAP Excellence – a real-time forecasting system to alert the Guadeloupe on potential flood events in the city. We are able to do this by simplifying technical processes and identifying potential flood locations daily.

Real-time forecasting and flood alert system interface simulating flood events at CAP territory © DHI

Real-time operation
The forecast management system created by the MIKE OPERATIONS platform automatically launches simulations daily with results available at 8 AM. The system provides:

  • Data on flood risks
  • Prediction of potential flood events
  • Alert emails to managers in a flood event
  • Visualisation of flood sectors for easy identification of flood location

Results

Real-time prediction of manhole overflowing over a 24-hour period

Dissemination of information through e-mail alerts and a dedicated website

Decision support system which increases the efficiency of CAP Excellence in flood management

About the client

Urban Community of Pointe à Pitre (CAP Excellence)

Software used

MIKE URBAN
MIKE OPERATIONS

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