FLOODING IN CAMBODIA
Design Challenge 2018 Contest
Phnom Penh Economic Zone, Cambodia
Pham Thu Trang
LET IT FLOW
A resilient city raised up from its territory assets
I. INTENTIONS FOR THE DESIGN
The site, located on the outskirts of Phnom Penh, offers many natural, industrial, cultural, economical and social assets. The PPSEZ is bordered by one of the four rivers of Phnom Penh; with an important rice producing along the Prek Knot River. The site is also close to several large-scale industrial sites such as the Vattanac Industrial Park along the road National 3rd and the Phnom Penh Special Economic Zone. Social studies show that sharing and helping are enhanced by the strong migration. Indeed, many young and single women come here for working. This is how the design of diverse scaled public areas and housings typologies had been thought.
Three main principles
Water resource should keep being a positive value, despite the weather and living conditions. The project aims to reconnect with the river, and to completely include water in the urban planning. The main concern revolves around the water quality and keeping the people and their home safe from flood risk while ensuring a stable economy.
The proposal aims to establish a connection between the site and the existing city, the industrial site and its territory characteristics, while creating various common spaces at different scales. We believe this can also be possible thanks to a design that considers the local lifestyle and materials as main assets and advantages that can be adjusted to the scale of the urban design.
In order to animate the new district and avoid a bedroom community, the master plan should ensure a homogeneous distribution of the equipments. The ground floor of the units will be containing shops, offices and restaurants, with an elevated electricity network and storage area. Housing or public facilities will be located above the maximum flood level as required by security rules.
We believe in flexible architecture, especially on greenfield sites. This is why, from a modular and replicable defined unit, the housing system is thought as a progressive plan that evolves following the family structure and the height of the buildings.
II . FUNCTIONING OF THE MASTER PLAN
The programme through a typical day recounting and hazard approach
Traditional Khmer architecture was designed in symbiosis with nature. So the vegetation is a full part of the project and river banks extend inside the project in order to recreate a kind of “garden city”, as Phnom Penh used to be.
The street network is designed according to the ancient land division and to the irrigation system, around a central buffer strip. In that way, the urbanism is the least exposed to flooding hazards.
As in the original Khmer villages, open air channels refresh the streets, to drain the excess water and allow the walkers to control the water level. Moreover, the permeability of the floor ensures a good management of urban runoff. That is the safest solution to prevent crisis situations (see below).
A regular day for the residents: leave the house built on stilts, walk along the open air gutters and the landscaped buffer strip in order to reach the floating market close to the embankment to buy fresh food for lunch. Sellers reach the lands during the afternoon by crossing over the river. After work, go shopping on the main road or rest at the neighbourhood park. Once home, spend a couple of hours either on the ground floor during the dry season from november until april, either on the elevated wooden corridor during the monsoon season from may until october. In case the citizens work far away from their homes, several parking lots are provided along the main road and under the houses. Moreover, most of the motorcycles and bicycles are parked under the housings.
One of the objectives of our proposal is to establish a connection between the future district and the existing “street-city”. This is why the embankment place and the floating market are located at the center distance of these two areas.
The design includes 2 of the 3 required scales to prevent flood: hazard, exposure and vulnerability. In fact, the topography of the project area is rising up from rivers to higher areas, making it easier for the water to be drained. The buildings are set on pilotis which makes them elevated. Along the river banks, Mangroves contain the ground and facilitate its permeability. Twice a day, people may observe the water level in the open air gutters. However, since the project is located on a flood site, the exposure is quite important.
Housing is protected from storms thanks to the surrounding vegetation such as banana and coconut trees. The structure design make buildings wind resistant.
When water is at its highest level, people could escape or be rescued from the elevated corridors and find refuge at the public facilities located at the highest areas of the district. They offer dormitories, and health care.
The longest distance from the emergency access is about 170 meters from the carriage road. This road 5m wide, which is enough width for emergency vehicles and garbage service.
This is how the local inhabitants or those coming from Phnom Penh may intuitively incorporate their territory functioning.
III. WAY OF LIVING
Between modularity and distinct identity
The aim of our proposal is to respect the local culture and lifestyle, but also provide comfort, ventilation and flood-safety conditions. We also focused on reaching the 3000 units’ target.
In order to do so, the designed housing is organized from a basic unit made out of a progressive living area and a wet block. Both are connected by a wooden corridor and can vertically evolve over time. Thanks to semi-collective staircases, families may extend their home by building upper levels. In that way, two families could overlap on two floors each. Two bedrooms respectively for girls and boys could be built on the third and fourth floor. This intermediate scale generates semi-individual housing.
The main area, that is the living area, contains a bedroom accessible from the living room that is arranged to receive guests. The whole plot revolves around a central Buddha figurine.
What we call the wet block is the unit that contains the kitchen and the shower-room. This system can vertically evolve over time. A part of the kitchen is located on a covered part of the corridor for natural smokes draining. The shower-room is close to the kitchen and visually more protected. In that way, a unique duct is necessary by superimposed 4-units group.
Characterized by a tropical climate, clocked by two seasons, the neighborhood is organized according to two scenarios: one during the dry season and another one during the monsoon season . Either people enjoy the ground floor, sheltered by the housing, with well-ventilated air thanks to the surrounding vegetation and near to little open air gutters, either they turn the first floor into the corridors during the monsoon season.
Structure description and dimensioning
The structural system consists of two first levels with a hard support structure for one even two additional wooden floors. The ground floor is made out of concrete pillars linked by visible strip footing to fit with the soft soil made out of sand and clay.
Both corridors and buildings are well-braced to resist to water strength, clay soil and wind thanks to strong concrete floors on the first two floors and wooden diagonals on the upper floors.The wooden framework is designed with as few screws as possible to provide a flexible structure on upper floors.
On the top of the topography, some buildings may be filled on the ground floor with breeze blocks keep the water out.
The different functions zones are compartmentalized by textile or light walls that can be made of wood, braided bamboo or palm tree. In order to protect open spaces from prying eyes, moucharabiehs are installed along the corridors.
The double sided roofs match the traditional Khmer roofing and make the rain water draining and catching easier. Metal sheets are used for temporary roof when a building is intended to be raised. The fourth floor roofs are covered with tiles to fix the maximum height. Shutters with orientated slats provide both solar and rain protection but also can keep the space cool in times of heat.
Thanks to this structural system, the inhabitants may organize their house themselves and use the materials according to their choices. It also ensures an heterogeneous development of this new area.
Material and labor costs
Many families may face financial difficulties building their homes. According to the PPSEZ survey report, 66% of the people would have to pay 100 to 200 dollars per month to buy their unit. About 40 years would be necessary to buy their house.
This is why an evolving strategy and phasing are necessary. At the PPSEZ scale and in addition to UNSIF and PPSEZ fundings, a cooperative could be established to crowd-fund the two hard structure levels and the corridors. Common spaces on the ground floor such as laundries and cellars under the wet blocks may also reduce the construction cost thanks to collective financing. This could also be interesting to introduce a solidarity between the inhabitants and a prevention system.
The district is adequately equipped:
A water ecosystem is planned to classify and differentiate treatments of the water species (drinkable water, clear water, rainwater, wastewater, industrial wastewater). At the northern gate and on the southern part of the project site, two water treatment plants are already established for the drinkable water. On the open air gutters, clear water can be led to the lands, to the public areas and to the shared gardens. At several urban spots, phytoremediation and aquaponics systems filtered this former grey water.
When the inhabitants have means to buy solar panels they can install them on the southern side of the roofs
Rainwater is caught from the gutters to collective water tanks installed on the ground floor.
Wind energy is useful for natural ventilation since the buildings are orientated to the North-South. In fact, dominant winds come from South.
Such a development of the city, in a respectful relation between Human and Nature, will lead to a sustainable and resilient district. In order to meet the flood hazard prevention and citizen uses requirements as closely as possible, our proposal for the PPSEZ is an environmental and local lifestyle friendly design.