Great strides have been made in addressing severe flooding during rainy season due to over-stressed drainage systems – Phnom Penh’s perennial problem.

On the confluence of three rivers – the Mekong, Tonle Sap and Tonle Bassac – the capital’s natural topography leaves it susceptible to flooding.

The economic costs were immense, with houses and markets submerged, while backed-up sewers created an unhygienic environment.

Flood protection and drainage infrastructure built during the French colonial administration and later in the 1960s were damaged, with poor maintenance during years of conflict exacerbating the problem.

The situation was further compounded by a rapidly increasing population density and the proliferation of high-rise buildings.

To address the problem, “Master Plan for Drainage Improvement and Flood Control in the Municipality of Phnom Penh” was formulated from 1998 to 1999 through the assistance of Japan.

The Project for Flood Protection and Drainage Improvement in the Municipality of Phnom Penh” – spanning nearly two decades – was first implemented in 2002 under the Japanese Grant Aid Official Development Assistance (ODA).

The objective of the project is to minimise flooding in the capital by improving its drainage system.

The ODA project covered the whole of Phnom Penh in four phases – the southwest in Phase 1, the north in Phase 2, the southeast in Phase 3, and the north and northwest in Phase 4.

Phase 1 (2002 to 2004)

In the first phase, in eight locations in the southwestern part of Phnom Penh, drainage sluiceways were installed, with ring dykes reinforced to prevent flooding.

Drainage was improved by repairing existing drainage channels and constructing new ones, while a pumping station with five drainage pumps were also constructed in the area.

Rehabilitation work covered a drainage channel stretching around 4.5km from the Boeung Salang Bridge to the New Boeung Tumpoung Pumping Station.

After the rehabilitation work, drainage has improved significantly.

Phase 2 (2007 to 2010)

In northern Phnom Penh along the Tonle Sap, four pumping stations were built to discharge excess water into the river.

Underground reservoirs were also constructed to temporarily store water at each station.

Some 4.4km of pipes were installed underground around Wat Phnom, Central Market and the Royal Palace – notoriously flood-prone areas in the past.

The wider new pipes significantly improve water flow.

Phase 3 (2012 to 2015)

A total of 20.1km of drainage pipes were installed in eight areas around Orussey, Boeung Keng Kang and Tuol Tumpoung districts under the third phase in the southeastern part of the capital. A sediment chamber was reconstructed to the southern side of the Royal Palace.

In this phase, equipment was provided to clean the drainage channels regularly, while maintenance and management training was carried out.

“Prior to the upgrading of the drainage system, residents constantly suffered due to flooding. Shaped like the bottom of a pan, the area frequently flooded when it rained, especially on St 166.

“However, after the rehabilitation works, the drainage channel drains water within an hour, even with heavy rain,” said Orussey 2 Commune chief Chan Piseth.

Phase 4 (2019 to 2021)

The ongoing final phase, which began in 2019, covers two areas in the northern part of the city, where flooding had been increasing in recent years.

In the northern part of the Wat Phnom area, 2.7km of drainage pipes are being installed, while a pumping station and underground reservoirs are under construction.

In Tuol Kork, around 7km of drainage pipes are being installed.

To further improve drainage, automatic screen pits are being installed at the four drainage pumping stations along the Tonle Sap River constructed in Phase 2.

Two mobile drainage pump trucks will also be provided.

Srah Chak commune chief Chhay Thirith said that with the adverse impacts of flooding having been reduced, the Japanese-funded project has made a great contribution to improving life in the community.

“The existing drainage system was old and small, so when it rained heavily even cars were half submerged.

“The new drainage system with the support of Japan means water discharges in a short period of time.

“And with garbage no longer floating everywhere during rainy days, the place is far more hygienic now,” he said.

The drainage built with Japanese ODA is helping protect Phnom Penh from the adverse impacts of flooding.

And it is the responsibility of every citizen to ensure it functions effectively, and not just the Department of Public Works and Transport, which manages the infrastructure.