Phnom Penh (1992-present)/ Hydraulic Infrastructure Development I

Phnom Penh has a rather lacking hydraulic infrastructure. Following its independence, the hydraulic infrastructure realized by the Municipality of Phnom Penh has been the only water system realized in the past 50 years. Till now, the Municipality has been aided by two major foreign technical assistance projects. Paris was the first to offer assistance in 1992 and has been ongoing since, while the second project was offered by the Japanese International Cooperation Agency in 1997 and is still ongoing. The projects proposed by the two parties are still largely in their infant stages however, and executing the actual plans is actually of an urgent need.

Aid from Paris (Aidtem)

Aidtem analyzed the water drainage system in Phnom Penh during 1994-1995, and reports showed that the drainage system of Phnom Penh is vulnerable in various aspects. It as noted that the Mekong and Tonle Sap Rivers during their flood stages had large volumes of water coursing through them during their flood stages, with their speed flowing at 40000 cubic meters per second and 8000 cubic meters per second respectively. This is a humongous amount of water, but Phnom Penh back in its early years was kept away from the force of such flood waters due to its formation on natural elevated banks of the river years ago. Urban areas only came to lie below normal flood levels as the city expanded into the low-lying areas behind the riverbanks. Creating successive dikes and filling in spaces between the dikes was therefore necessary in protecting such areas. However, inadequate drainage capacity in such artificially raised areas has become the primary flood risk to the city today.

“prek” and “beng” – where did they go?

In a previous post, it was mentioned that Phnom Penh possessed a water management system involving a network of “prek” and “beng” that could collect and drain rain water. One may wonder what does such a system do nowadays in contributing to the drainage capacity of the city. Truth is, the system which was carefully planned and calibrated once upon a time was only sufficient to keep the water flow at its equilibrium in a fragile manner, and is no longer in function even though they are physically present throughout the city. The drainage system is currently obstructed with garbage and household waste, or is replaced by new constructions that have filled in the “prek” and “beng”, disregarding the previously existing system. Only three “beng” (Beng Kak, Beng Salang and Beng Trabaek) remain in the city, among which two serve as drainage areas for used water as well as reservoirs for rain water.
Aidtem study and its proposal

Lacking basic data actually made it hard for researchers to come up with a plan. Planners have resorted to directly assess on site , and has come up with a numerical model for simulating different flood conditions. It has divided the research into several districts, with the following being some of the major areas prompting attention:

Daun Penh
The study concluded that water drainage systems in Daun Penh can be rehabilitated. Clearing obstructions in the existing system and adding an extension to the current system would allow for a new system exclusively for draining household water to be created, draining towards Beng Trabaek’s basin. A new system to drain rainwater can be installed parallel to Tonle Sap river, which allows for water from the district to run directly into Tonle Sap.

Tuol Kok
Drainage system in this district is inadequately developed. Drainage systems are suggested to be extended to cover the whole district, while pumping stations could be installed to control the flow of rainwater in canals. Another network of pipes is to be installed to collected household water to connect to the main drainage system sketched in the master drainage plan for the city.

Basin near Beng Salang
Beng Salang is reported to hold a capacity of 150000 cubic meters of water if well managed. A system using storm gutters to separate rainwater from household waste is proposed to be installed at the entrance of the “beng”, while household water would be pumped into a new network of channels along the “beng’.

Basin of Beng Trabaek
Beng Trabaek can hold up to 500000 cubic meters of water if managed properly, and flood gates are to be installed to regulate the canals in the area to regulate the flow so excess water can be conducted to Beng Trabaek station where it passes out under the dike.

Conclusion from Aidtem study

It can be seen that the systems laid out in earlier years of the city’s formation actually works – and can actually hold quite some volume of floodwater. It is the lack of maintenance and understanding from the general public of such systems that has led to its deteriorated state today. Water was once a communal resource but its management has evolved to be random without logic according to the needs of individuals, instead of a collective. The systems are not entirely irreversible though, as they could still be restored by clearance or extension along with possible construction of new drainage networks. The emergence of a party to specialize in maintaining the system is important to restore the equilibrium of water flow within the bounds of Phnom Penh.

Reference:

Molyvann, V. (2003). Modern Khmer cities. Phnom Penh, Cambodia: Reyum

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