Definition

A sea outfall is a closed pipeline for the transport of partially treated wastewater from the treatment area located onshore to the discharge area generally located offshore at a certain distance and depth to facilitate rapid, high and efficient initial dilution so that such discharge does not pose a health risk or have harmful effects on the local ecosystem.

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The above definition is extensible to pipelines whose discharge areas are located in rivers and lakes, although these are less common and efficient than the previous ones.

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Within the wastewater set we can include those waters derived from an industrial process such as cooling water, brine, etc., and those derived from an urban or domestic process such as sewage, rainwater, etc.

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The execution of a sea outfall generally involves the combination of two or more construction processes that vary according to the type of installation to be carried out, and may be, through trench installation, laying of the conduction directly on the seabed, lake or river and/or, more recently used, through trenchless technologies.

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As a reference and to understand better the need to combine several construction processes during the installation of the pipeline, keep in mind that generally the discharge area is usually located at a distance that varies between one and four km from the treatment area and whose discharge point is between twenty and seventy meters below sea level.

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Other factors to consider for the installation of the pipeline are, among others, the geology, oceanography and orography of the seabed and the environmental conditions and restrictions of the area through which the outfall runs.

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In the execution of sea outfalls, generally the conduction in its terrestrial part is carried out buried so that both the trench installation and the trenchless installation will be used according to the techniques described below and in the maritime part the laying of the pipe on the seabed is added to the previous ones.