NA-05 - Cleaning: Cleaning Strategy and Programme

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Fundamentals
Cleaning measures
Development of the cleaning plan
Cleaning strategy
Optimization of the cleaning effort
Determination of cleaning intervals
Summary

Determination of cleaning intervals

System and Network data – Example invert gradient

Example: The invert gradient of individual lines or line sections can be the first determining factor to the self-cleaning capability and the wall shear stress in a given area of the sewer system.

Image:

Grouping of the sewer network sections based on invert gradient [Source: visaplan GmbH]

Source: visaplan GmbH

Graphical material and visualisations visaplan GmbH, Bochum, Germany (www.visaplan.com).

1 First section (invert gradient 0.3% up to 1.0%)
2 Middle section / branch sewer (invert gradient 0.20% up to 0.30%)
3 Final sections of the sewers / main sewers (invert gradient 0.1% up to 0.2%)

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Based on these network data, sections can be sorted according to specific features and subdivided into groups or types. For example, the invert gradient of individual sections and subsections can help to estimate the level of self-cleansing and wall shear stress in the relevant area of the sewer network.

Normally, the invert gradient of a sewer in its entire course up to a main sewer, sewage plant or pumping plant is chosen such that the upper sections, with the smaller nominal sizes and the lower water bearing capacity, are installed with a steeper gradient than the midlevel and lower sections, because, in these areas, a larger and more continuous discharge as well as a higher wall shear stress can be anticipated. If the wastewater flowing in a section does not have sufficient wall shear stress, there will be deposits.