Drainage trench

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Terms & Synonyms

Official WHO Definition

A drainage trench is a drain that is surrounded by stone or other inert material used as a soakaway for liquid dispersion (WHO 1992).An excavation, cut below the ground surface for the purpose of installing a drain or drainage system (World Plumbing Council Working Group 2008).

Other Definitions


Interpretations and Explanations

Soil pores eventually become clogged by effluent from pits or drainage trenches. This may reduce or even stop infiltration through the soil. The soil type and the level of the groundwater table relative to the liquid in the pit or trench affects the rate at which liquid infiltrates from pits and drainage trenches. Opinions vary regarding whether the base or sidewalls of drainage trenches or pits are the primary areas through which infiltration takes place. The effluent from pits and drainage trenches may contain pathogens and chemical substances that could contaminate drinking-water supplies. Because of their comparatively large size, protozoa and helminths are rapidly removed by the straining action of the soil, but bacteria and viruses are more persistent. Effluent passing through unsaturated soil above the groundwater table is purified by filtration and by biological and adsorption processes. Filtration is most effective in the organic mat where the soil pores are clogged. The passage of pollutants from a new pit or drainage trench reduces as the pores become clogged. Unsaturated sandy or loamy soil below a pit or drainage trench is likely to provide an effective barrier to groundwater pollution (WHO 1992).A drainage trench is required when a drain for a single domestic dwelling is installed below ground between the dwelling and the authority’s connection point (World Plumbing Council Working Group 2008).


WHO (1992) A guide to the development of on-site sanitation

WHO Lexicon page (translations and examples)

See also

External Resources


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