Additional elements regarding the muddy layer in combined sewers

For 25 years, major efforts have been undertaken to improve the basic knowledge of solid dynamics in sewers. However, various aspects still require further research. The French national project "SER" was conducted from 2009 to 2012, in providing the opportunity for new experimental set-ups to enhance knowledge of solid dynamics. The present work has originated from this "SER" project and benefited from the various research tasks completed. The experimental site and set-up are briefly introduced before displaying the daily dry weather pattern of the muddy layer observed at the top of the deposit. A discussion is provided on the conditions most favourable to the constitution and origin of such a layer. A mass balance is also presented, showing that the muddy layer is moving into the sewer network on a daily basis.