The blue pearl of Asia : flooding as an urban asset : a beautiful and resilient future Phnom Penh

Sammanfattning: Surface water drainage is together with water supply and wastewater management key parts of infrastructure in urban areas. As landscape architects we aim to find solutions that envisage aesthetical, social and ecological perspectives as well as technical. These aspects often go hand in hand and together they are part of the sustainability concept. Phnom Penh was in the sixties known as "the Pearl of Asia". The capital of Cambodia incorporated many green areas and water features and the architecture was blooming. After many troublesome years of cruel regimes and war the city is now degraded and the infrastructure is badly maintained. Corruption is widely spread and private construction companies are ruling the construction market and the urban planning. The city is located on wetland by the conjunction of four great rivers. There are two dominating seasons, wet and dry and they shape the prerequisites for the city planning. Precipitation is a huge problem in the rainy season and most of the urban storm water is together with the city wastewater lead through open canals or drainage pipes to the surrounding wetlands. The wetlands biologically clean the contaminated water before it enters the rivers. The wetlands also possess great water storage capacity. Phnom Penh is protected from flooding by embankments (dikes). The urban storm water reaches the wetlands through sluiceways in the dry seasons. The sluiceways are closed during the rainy season to prevent the city from flooding and the storm water has to be pumped over the dikes. Due to poor urban planning, corruption and increased land prices, the public green and blue areas in and around the city are rapidly disappearing and inundation of the city has become an enormous problem. New satellite cities have popped up in the wetlands and there is a shortage of public parks and spaces in the city centre. The water storage capacity of the wetlands has diminished due to constructions and polluted water reaches the rivers without cleaning and many sensitive ecosystems are lost. Urbanisation is a fast ongoing process in Phnom Penh. The city needs to expand to cope with its increasing number of inhabitants. Development and expansion put a huge strain on the urban ecological and social structures. To protect and keep the sensitive ecosystems of the urban wetlands and lakes, a future city expansion must be well considered and the development should occur in phases. An ecological storm water management tries to imitate nature as far as possible and use the prerequisites of the site. As much as possible of the storm water is therefore taken care of locally in an ecological storm water design. Urban environments generally consist of a majority of impermeable surfaces, which prevent water to infiltrate. New development in Phnom Penh would benefit from ecological storm water design. The pressure on the under dimensioned drainage system of the city would lessen and problems with inundation be reduced. If polluted water was taken care of locally, emissions in the sensitive rivers would diminish. Urban infiltration areas and storage ponds could be incorporated in future urban design. Since flooding is an unavoidable occurring event in Phnom Penh, the city would benefit from adjusting to the rising water levels instead of fighting against them. Floodable areas incorporated in the urban design are efficient in dealing with the problem of inundation in the streets as well as a beautiful variable design feature. We have chosen two sites in Phnom Penh that soon are about to be developed for construction Boeng Cheung Ek and Boeng Kak Lake. These two areas are both hydrologically interesting. They are located on low points in the city and today they serve as natural water storage features. Our thesis resulted in two design proposals that incorporate an ecological storm water perspective as well as a sustainable city perspective.