Flood Mitigation Scheme:

Buildng Detention Ponds in Tutong District

In a strategic move to mitigate flooding and protect villages from flood damages in Tutong District, the Government of His Majesty allocated significant funds to flood mitigation projects. This initiative led to the construction of three vital detention ponds in the district’s upstream areas.

Project Overview: The project focused on three main basins: Maya Basin, Pemandang Basin, and Ligi Basin, ranging in size from 12.8 km² to 27.3 km². Traditional land surveys for such large areas were deemed impractical due to cost and time constraints. Instead, advanced LiDAR survey data was utilized and converted into .DWG files for comprehensive catchment studies.

Data and Modeling: Rainfall data from stations at Brunei International Airport, Ukong in Tutong District, and Miri International Airport was used to set up the HEC-HMS model. This model simulated and estimated surface runoff under various rainfall intensities and Annual Recurrence Intervals (ARIs).

 

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Innovative Design and Construction

The project’s innovative approach included selecting strategic locations for bund embankment to detain runoff, thus regulating and reducing sudden surges of water from heavy rains. The bund embankment were designed to withstand run off with a 100-year ARI, featuring a 700 mm freeboard for added safety.

  • Constructed over soft ground, the embankments base were reinforced with high-strength woven geotextiles. With gentle slopes of 1:5 and counterweight berms, the design minimizes the risk of slip failure. Embankment lengths range from 340 m to 520 m, with heights between 4200 mm and 4600 mm.

Additionally, Reno mattresses protect the slopes from water ingress and scouring.

To ensure natural discharge capability and minimize maintenance issues associated with regulated penstock with telemetry control, the ponds were designed with multiple discharge outlets at varying levels. The lower level had one outlet, while the upper level had two, allowing effective water discharge during different stages of water level rise. Additionally, a rectangular-shaped spillway was integrated to handle excess water, reducing the spillway length required along the bund.

Project Details

  • Number of Detention Ponds : 3        
  • Location :  Tutong District
  • Basins :  Maya, Pemandang, Ligi
  • Project Duration :  18 months
  • Cost :  BND 6 million
  • Client ：Department of Drainage and Sewerage, Public Works Department,            Ministry of Development