Carlos's Blog: Live with floods: The settlements of the Vietnam Mekong Delta

Floods often occur in rivers, when flow exceeds the capacity of the river channel, particularly at bends or meanders. Floods often cause damage to homes and businesses if they are placed in natural flood plains of rivers. While flood damage can be virtually eliminated by moving away from rivers and other bodies of water, since time out of mind, people have lived and worked by the water to seek sustenance and capitalize on the gains of cheap and easy travel and commerce by being near water. That humans continue to inhabit areas threatened by flood damage is evidence that the perceived value of living near the water exceeds the cost of repeated periodic flooding.

About one million hectares of the Delta is inundated by more than a meter of water every year. Learn how theVietnamese government has tried to manage this natural phenomenon. Same same but different,” is the common Vietnamese phrase that means similar but not the same. In many aspects, the Mekong Delta of Vietnam looks similar to rural.

The water related natural disasters in the Mekong Delta can be divided into "flood (or submergence)" and "saline intrusion" roughly. The word, "flood" means a phenomenon that excess river waters originated from upper stream submerege the area of inner dike in general. However under the condition of the strong didal influence toward inland rivers and canals like the Mekong Delta, the flood tide also could cause a flood. Therefore both of flood waters from fresh water basin and saline intrusion make the same output of "flood" to the society, whereas the mechanism of each natural phenomenon are completely different. As an essential major premise, the saline intrusion is very characteristic and important phenomenon to understand the natural status in the Mekong Delta.

The coastal sea of the Mekong Delta, the South China Sea, is well known

with its large tidal difference in seawater level, and the differential exceeds 4.0m in maximum. Under the condition that the most area of the Mekong Delta has only several meter in the height above the sea level, this large tidal movement has great influence to inland area, especially in the rainy season when the river waters from upper stream also increase. While the change of water level due to tidal movement extend to Kompong Cham in Cambodia which is located at the upper 410km point from the sea along the main rivers, the intrusion of seawater itself can reach about 60km far from the sea2). In the meantime, Thailand Bay that face to the west coast of the Mekong Delta has only less than 2.0m in its tidal differential, therefore, the waters from the South China Sea thuroug the rivers and inland canals easily flow into Thailand Bay (from a specialist in irrigation teaching at a collage in Can Tho City).

At the above figure, the area intruded by seawater all the year around is the coastal edge from the estuary of Dong Nai River (Can Gio District which is well known as a UNESCO's natural reserved are) to Ha Tien near the Cambodian boder. Particularly in the Ca Mau peninsular, the area over 30km from the coastal line are influenced with saline, and it is very hard to produce agricultural crops. Meanwhile, the three inner belts are seasonally intruded by saline, and each degrees depends on the distance from upper side or main streams.

The Mekong Delta ofVietnam is a result of 10,000 years of gradual d

eposition of sediments carried by the Mekong River and its tributaries from as far north as Tibet on its way to the South China Sea. Located at the southern tip of the Mekong River system, the Delta has an area of 3.9 million hectares, expanding at the rate of 10 to 20 meters per year. It is home to almost a quarter ofVietnam’s population (16 million) with a density of more than 1.5 times the country’s average.About half of the land (1.9 million hectares) is inundated annually. During rainy season inundation above one meter covers about one million hectares of land. Within the river basin, the highest flood levels can reach up to six meters and last for six months. During the dry season, saline water intrusion spreads from the coast to 40 to 50 kilometers inland, covering an area of about two million hectares (20,400 square kilometers).

Land use in the Delta is dominantly agricultural (75 percent) while residential land covers only 2.5 percent.The agricultural production of rice and shrimp is noted along the banks of Hau and Tien rivers and the coast of South China Sea where alluvium (38.09 percent) and saline soils (18.04 percent) are found respectively.The unproductive and dominant acid sulphate soil (43.20 percent) occurs in the northern low-lying region of the periodically inundated Delta. Peaty soil (0.67 percent) in the south and western region are planted to melaleuca trees, a host to a high-value saprophytic snail raised for export, and home to migratory birds.

Though the Delta is a highly critical environment it still serves as the country’s rice bowl in the south. It also contributes 80 percent to the country’s total shrimp production area. Under the economic renovation policy, shrimp and rice exports are seen as the country’s ticket to economic recovery.The economic opportunities attract more people to live in the Delta and embark on shrimp and/or rice farming.

In support of its economic objectives, and the increasing population in the Delta, the Government resolved to “live with floods and aim at flood control,” in order to p

rotect people and maintain normal lives during inundation. In this policy the approach is structural, aiming to control rather than work with nature, despite criticism from environmentalists. Flood control structures include: dams, dikes, sluices, and canals built to protect crops and properties; and residential clusters/dykes.A residential cluster is a dike protected region of two to three hectares in area provided with foundations elevated 0.60m above the highest flood line, roads and drainage, and basic house and utility lines for resettlement of households in dangerous and flooded areas. A residential dyke is a linear development along a river, channel, or main road.

Non-structural measures to mitigate damage by floods include:
• Strengthening flood and storm preparedness organizations;
• Flood forecasting and warning on the flood situation in each area;
• Emergency relief during and after flooding to stabilize people's livelihood as soon as possible and get prepared for the forthcoming floods.
• Training courses and workshops on disaster preparedness and mitigation for disaster management officers.
• Improvement of public awareness on disaster management and mitigation through leaflets; and
• Research on disaster mitigation measures such as study on the shifting of cultivation timing to mitigate crop losses.

The government formulates a master plan (a strategic non-structural plan) to apply collective preparedness, response, adaptation, and evacuation measures.Vietnam learns from disasters by undertaking timely damage assessment, flood level monitoring, and updating its hydrologic and topographic data as tools for better disaster preparedness and disaster risk management.

The coastal area of Southern Vietnam is a wetland. With minimum infrastructure, materials for houses (such as mangrove branches) are collected around the area.Water comes from a deep well and electricity is provided by transmission lines from the city carried over rivers by towers. Life is simple and strongly related to water.

The Hoa Binh Resettlement Project is located at the confluence of three rivers,Tien, Hau and Vam Nao in Phu Tan District,An Giang, a part of Lower Mekong Basin. It is subjected to inundation of up to four meters for a maximum of six months. It is part of the North Vam Nao Flood Control Project. Resettlement approaches here include:
• Project design readjustment to minimize impact;
• Near-site resettlement to minimize dislocation; and
• Land and house compensation in residential cluster.
The Gia Vet Resettlement Project is part of the Coastal Wetland Protection and Development Project in Duyen Hai District, along the coast of Tra Vinh. Households were relocated from Full Protection Zone (FPZ) to a Buffer Zone.The resettlement approach here include:
• Land and house compensation in residential dyke;
• Integrated shrimp production;
• Provision of utilities and school; and
• Mangrove reforestation to restore marine ecology and provide wind and storm buffer.

The Ho Gui Resettlement Project is for households located in erosion and landslide prone areas (near the confluence of Ho Gui River and the South China Sea). It is the poorest settlement in Nam Can District, Ca Mau.The resettlement approach here includes:
• Disaster-resistant house design;
• Provision of wind/storm buffer;
• Raised mound/foundation;
• Inner channel construction;
• Provision of utilities and amenities such as health clinic, primary school, and market

The Vietnamese approach to settlements in the Delta is strongly influenced by structural flood mitigating measures. Site development is guided by the up-to-date information on flood levels taken from gauging stations, typhoon path and tidal flows. Houses are built on engineered sites and are assumed to be on safe ground. Hence, design is typical and does not consider the presence of water.

Structural measures immediately address the impact of flooding to life and property. But these can disrupt natural processes, resulting in adverse environmental impacts such as:
• Disruption of natural overbank flows, and the periodic flooding deposit of fertile soil to rice fields. Dike construction deprives fields of natural fertile soil suitable for farming which may result to increased use of fertilizer.
• Exposure of potential acid sulphate soils to air during canal and sluice excavation, resulting in acidification of soil and eventually water.This may result in the depletion of soil nutrients making it unsuitable for farming. Canals and sluices also block seasonal fish migration depriving schools of fish of a spawning sanctuary which may lead to a reduction of fish species in the Delta;
• Increased water flow results in rapid sedimentation at river mouths causing channel bank erosion on one side and accretion on the opposite bank, resulting in channel migration that causes changes in the course of water ways.
• Construction of canals facilitate increase in salt water intrusion through faster subsurface penetration of saltwater, affecting agricultural production. For settlements development to be sustainable, it must consider social development, economic development and environmental preservation.

The socio-economic considerations for sustainable settlements development in river basin and coastal areas include: provision of access to material and financial resources, services and amenities; maintenance of social structure that provides support in times of crisis; and the maintenance or improvement of quality of life. Considerations for environmental preservation include: the protection/rehabilitation of mangrove forests; provision of environment-friendly flood mitigation measures that allow natural ecological processes to take place; application of organic riverbank erosion control measures to avoid sedimentation and rapid bank erosion; and waste management.

Physical considerations include site conditions, such as surface water level, volume, source and direction of flow, and quality; climatic conditions influencing wind speed and direction; soil bearing capacity; presence or provision of buffer zone in environmentally sensitive sites; provision of basic services and amenities; accessibility to water or land and limited mobility; and use of light weight materials for construction. It is also important for a team of specialists to work together to have a better understanding of the coastal and river basin environments and together formulate possible solutions.