Drainage in the Four Faces

Runoff Zones

Source: Molyvann, Vann. Modern Khmer Cities. Phnom Penh, Cambodia : Reyum ; [Chicago, IL?] : Sales and distribution, USA, Art Media Resources, c2003

p125

“Water drainage remains a critical structural problem for an expanding Phnom Penh as well. If very high floods on the Mekong River surpass the capacity of the present pumping system of the city, a catastrophe could ensue. in the 1960s, Phnom Penh developed a viable system of water drainage which included a network of pipes to drain both rain water and used household water. In addition, existing prek and beng were included in this drainage system which allowed rain water runoff as well through the use of pumping stations. Today, due to lack of maintenance, the existing drainage networks are almost completely blocked. Used household water and rain water accumulate in drains during the rainy season rather than running through them, causing flooding in many parts of the city. Improperly managed flood water inundate areas surrounding the city, thus limiting the amounts of water which can be pumped out of the central city into zones. Drains and canals leading to the beng or ponds inside the city which do still serve to hold excess water are obstructed or saturated so that rain water has to run directly onto roads, causeways and dikes to reach these reservoirs. The causeways and dikes thus only hold for one rainy season and must be repaired each year. Pumping stations are neither numerous enough nor powerful enough to adequately fulfill their pumping functions.”

“The drainage system established in the 1960s combined rain water and used household water into a single system. The system only served the central area of Phnom Penh as well as sections of the city located towards Beng Trabek and Beng Salang. Drainage in Tuol Kok at that time remained a simple network of open drains. The central drainage system of the 1960s did not include the area of Beng Tompun either. The dike of Beng Tompus was constructed in the 1970s as a military defense agains the Khmer Rouge. Beng TTompun receives water from the higher plains and from area around the airport. This water is channeled into the Meanchey River (a natural canal) along with water coming from Beng Salang and the area around the Khmer-Soviet Hospital. SInce the areas of Beng Salang and Beng Tompun lie at similar levels are separated by a high dike, pumps must be used to lead water into the larger Beng Tompun. Today Beng Tompun is ringed by spontaneously built shanty towns with more than 40,000 people living in extremely precarious sanitary conditions”

“The system of building dikes and then pumping water from one low-lying area to another in order to move water away from the city is not an infinitely extendable system. During heavy rains, flooding in Phnom Penh at present can cause a third of the city to be paralyzed. It is of great urgency to stop such flooding and to improve drainage at the center of the city. In the case of exceptional flooding, it will be necessary to evacuate hundreds of thousands of people.”

“Even in the zones outside the dikes of Phnom Penh, the natural system of beng cannot be maintained. Instead, a new system of drainage must draw runoff surface water from the urban areas behind the river banks towards Prek Phnou to the north and Prek Thnot to the south. The low-lying urban areas of Phnom Penh, located behind the banks of the rivers, from a large rectangle measuring about twenty kilometers long and ten kilometers wide. The building of dikes around the city has created an obstacle to water running off from the higher plains toward the Tonle Sap River. The dikes channel these waters into the beng to the north and south of the city, obstructing water flow toward the rivers.”

“National Route 4 from Phnom Penh to Sihanoukville forms a spine separating the great plain of low-lying fields behind the river banks into two sections. The northern section is drained by the Prek Phnou while the southern section is drained by Prek Thnot. The two prek must be expanded in order to drain all the runoff water from each of these plans. National Route 3 helps to lead runoff water towards Prek Thnot which National Route 2 running along the river bank to Takhmau, serves as a dike against hte floods of the Bassa River By establishing adequate management over the Prek Thnot and Prek Phnou, a mechanism for flood control will be put in place in Phnom Penh.”

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