Simplified Sewerage - Design and Construction

Design and Construction

Simplified sewers are usually laid in the front yard or under the pavement (sidewalk). In some rare cases it is possible to lay them in the back yard. Sidewalk branches are usually preferred in regular urbanizations, while the front and back yard branches are particularly suited to neighborhoods with challenging topography or urbanization patterns. However, in some cases neither of these options is possible. For example, in South Asia, in many cities there is no sidewalk or front yard, so pipes have to be laid in the middle of the street as with conventional sewers.

In Latin America typical simplified sewer diameters are 100 mm, laid at a gradient of 1 in 200 (0.5 percent). Such a sewer will serve around 200 households of 5 people with a wastewater flow of 80 litres per person per day. In Pakistan, however, there are no rigorous standards for sewer diameters. In a small pilot as part of the Orangi Pilot Project pipes with a diameter of 150mm were used.

Laying small diameter pipes at fairly flat gradients requires careful construction techniques. Plastic pipes are best used as they are more easily jointed correctly. This reduces wastewater leakage from the sewer and groundwater infiltration into it. With simplified sewerage there is no need to have the large expensive manholes of the type used for conventional sewerage — simple brick or plastic junction chambers are used instead.

Construction can be carried out by contractors or by trained and properly supervised community members. Training and proper supervision are actually needed in both cases, since contractors in many cities are not familiar with simplified sewerage.