Flood Forecasting on the Lower Chao Praya River

Bangkok, Thailand, April 28, 2004

There is an impression that the development of an operational Flood Forecasting System is a massive task, inevitably requiring extensive and expensive consultancy and a system based on bespoke software and international bank support. The rapid and inexpensive development of an operational Flood Forecasting System for Thailand’s Lower Chao Praya River, built around Wallingford Software’s InfoWorks and FloodWorks suites, shows that a scaled down approach can deliver excellent results within more practical timescales and budgets.

In the past Bangkok, a major city of 12 million population, has regularly experienced a flood season during the monsoon from mid-September to the end of October each year. The cause is the Chao Praya River, which flows for 370 miles (600km) from the north of Thailand to Bangkok, fed by the Nam and Ping rivers. Flowing through the center of Bangkok shortly before reaching the Gulf of Thailand, the lower reaches of the river provide an essential highway for the transport of people and cargo. The huge river basin takes more than a month to flow from source to the Gulf, has a catchment of 62,000 square miles (16 million hectares), and an average annual rainfall across the catchment of some 50 inches (1270 mm), with a high proportion falling in the monsoon season. The result is flow discharges than can exceed 6500 cubic yards (5,000 cubic meters) per second.

Flood forecasts had previously relied on engineers making hand calculations of the flood threat based on daily readings of river levels. In 1998 plans began to build a system to address this threat more formally, and the Hydrodynamic Flow Measurement Project was conceived.

The initiative came from the Thai Royal Irrigation Department, and the project was jointly funded by the RID, the Office of the Royal Development Projects Board and the National Research Fund. The project team comprised AMR Asia Co Ltd as main contractor and supplier of telemetry / SCADA equipment, Water Development Consultants Ltd (WDC), a local company providing consultants, modelers, and flood forecasting experts, and Wallingford Software. The selection of Wallingford in preference to the competitive offerings was based on its high functionality, powerful existing links between the river modeling and flood forecasting modules, affordable price, and the local language capability of the software.

The project began in 2001, with the resultant system to be built around two central off-the-shelf software packages. InfoWorks RS accurately simulates river flow and its behavior in its channel and flood plain under different weather assumptions. FloodWorks provides real-time operational support in the control room, running on dedicated hardware. It estimates detailed flood risks, forecasts flood levels, and the handles the administration details of flood warnings, with particular emphasis on urban flooding, all within the very tight timescales required of a flood control room in action.

The active forecast area of the system is from Ayutthaya, some 60 miles northeast of Bangkok, through Bangkok to the mouth of the Chao Praya River and the Gulf of Thailand. There was already a network of 25 telemetry sites monitoring water levels and rainfall, and the new project required only 8 further sites to give the coverage needed. In addition, new communications links were established to existing Bangkok Metropolitan Administration and Public Works Dept telemetry systems along the river.

The offices of the RID in Samsen, Bangkok were selected for the master station of the new flood control system. The central system was installed here - a dedicated server and the FloodWorks and InfoWorks RS software. The client interface - FloodWorks Event Manager - was installed in this control room (2 copies) and also the two additional offices of the Bangkok Metropolitan Administration (BMA) and the Office of the Royal Development Projects Board (Kings Office).

The project went live in 2003 on time and on budget, and the first monsoon period past with no major flooding. Clearly this was not as a result of the system - the system is to manage floods, and cannot completely prevent them in a very wet year - but the RID is reassured that, when floods come, as they will, the very best flood management and flood warning system is in place to minimize the impact.

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