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3.2 Collection and transfer (Topic b)

3.2.1 Sewer and drainage system

In most situations, gravity sewers following the natural topography are used for collecting sanitary sewerage. The components of a typical system are:

The earliest recorded drainage and sewerage developments in the Asia Pacific region were constructed as combined sewerage systems for old cities. This was an accepted design practice in the early 20^th century and provided an economical solution to the wastewater collection problem. Many systems were designed to serve only stormwater. As communities grew, many people discharged their sanitary waste into the stormwater drainage and sanitary sewage was then conveyed to natural receiving water. With increased population, the large volumes of sewage being discharge led to water pollution problems. Wastewater treatment was then necessary.

The existing drainage systems, which almost entirely consist of combined sewers without pumping stations, drains and canals, are generally in poor condition due to lack of maintenance. They are poorly designed and constructed, without sufficient hydraulic capacity. Drainage coverage is unevenly developed in the various cities. The length of trunk sewers per hectare and per person are useful indicators, which show that the extent of trunk sewers in most cities in Vietnam is about one-fifth to one-tenth of what would be required for a well sewered city.

Sustainability in urban areas will not be achieved without adequate supply of water and sanitation facilities to support the livelihoods and health of the residents. In recent years, many Asian cities have suffered from inadequate infrastructure, including water treatment and supply. The problem has become chronic in the wake of burgeoning urban populations in the large cities, where sewerage projects have lagged behind relative to population growth (see Table 3.6).

At present sewer and drainage systems in most of the developing countries in the Asia Pacific region such as India, Bangladesh, Sri Lanka, Nepal, Philippines and Vietnam are in very poor condition. Those systems were constructed during colonial times, and need to be upgraded and/or extended. For example in India at present, the sewage network in Mumbai consists of almost 1381 km of main sewage line combined systems, and 51 pumping stations (Parekh, 1995).

The earliest records of drainage and sewer developments in Vietnam trace back to the 1870s in Ho Chi Minh City (HCMC) and in the year 1905 in Hanoi, when French engineers planned and constructed the first combined sewers. By 1938 about 11km of pipes had been installed in Hanoi, which at that time had only 150,000 people living in an area of about 1000 hectares. That corresponds to the same level of drainage development as in Class II and III cities in Vietnam today. The drainage system was extended in steps with urban growth during the French period up to 1954, when France gave up its colonial power in Vietnam.

The sewerage system was constructed in the old city from 1905 to 1945, and in the new residential areas after that period. According to the Study on Urban Drainage and Wastewater Disposal System in Hanoi City, the total length of drainage pipe had increased by more than ten-fold to 120 km in 1989, and at about the same level of development as today 29 m/ha (0.13 m/person). The population increased by six-fold to about 900,000 over the same period (VNUWCSS, 1995).

According to a Sewerage Feasibility Study for Saigon City carried out in 1971, Saigon's drainage system consisted of 112 km of pipes in 1970. In 1989, the total length of drainage pipes in the city had increased to 450 km, covering an area of some 14,000 ha and serving a population of 2.8 million. The HCMC Urban Drainage Company is reported to operate and maintain about 500 km of pipes with diameter larger than 400 mm, and an additional 400 km of smaller diameter pipes are taken care of by district authorities. The system consists of 100 km (20%) that are older than 100 years, 250 km (50%) that are 30 to 100 years old, and only 150 km (30%) that are less than 20 years old. The same rapid expansion of the drainage systems has apparently not taken place in other urban areas in Vietnam. In 1975, the cities of Hue, Da nang Nha trang, Phan thiet, and Can tho had a combined drainage pipe length of about 39 km serving a population of about 625,000 people, or 0.06 m/person, which is about the same level of development as today (VNUWCSS, 1995).

These conditions are not unique to the towns of Vietnam only. In the Philippines for example, the Ayala city service area comprising 700 hectares, has 7 trunk lines, 4 overflows, 1,142 manholes and 70 km of pipeline with diameters ranging from 100 to 1050 mm, all of which are in such poor condition that 1060 manholes require urgent replacement. In Metropolitan Manila, only 11% of the population have access to the sewer system.

Although most of the developing countries have poor wastewater collection systems, there are some parts in Thailand and Indonesia where innovative projects for the improvement of sewer and drainage systems have been implemented. For example:

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