Drainage trench
- Slovak term: Slovenský termín
- 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).
Explanation
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).
Example
A drainage trench is an excavation, cut below the ground surface. The base of the drainage trench must be constructed with grades or falls. The grades enable the gravity forces in the drainage system to work. The grades are calculated by taking into account the hydraulic loads and size of the drain pipe. A drain must be installed with deeper than a minimum cover to protect it from future damage. The depth of the cover required is specified in plumbing codes. A trench is also used to protect other easily damaged and services, such as water supply, gas supply, power lines and data lines (World Plumbing Council Working Group 2008).
