Assessment of the functionality of geotextile and granular filter systems in hydraulic engineering in case of iron ochre clogging tendency

In recent decades, there have been individual cases of damage to geotextile filters due to clogging by flocculated ochre products. This process is defined as ochre clogging and has been extensively explained in recent theoretical studies (Tophoff et al., 2022). Several revetments of tidally influenced German North Sea estuaries have been damaged due to a severe reduction in the permeability of geotextiles. Therefore, experimental investigations of granular and geotextile filter constructions were carried out to better understand filter clogging. The investigations reproduce a revetment section at a scale of 1:1. For this purpose, the clogging process in the fluctuating water level or clogging zone was reproduced as a purely chemical iron precipitation. Ten short-term tests (10 h) and one long-term test (50 h) were carried out in total. The tests show that the process involves internal clogging and that the iron precipitates adhere immovably to the filter structure, reducing the pore space and permeability of the filter. This process is considered less problematic for granular filters. A reduction in permeability was measured in some cases for geotextile filter designs. Different geotextile material parameters appear to influence the iron ochre clogging tendency.