Sediment Deposits In Sewers Research Articles

Organic near-bed fluid and particulate transport in combined sewers

Studies in Germany, Belgium, France and Scotland have revealed that there are significant solids transport gradients in the depth of foul and combined sewage flows. Continuous field observations of changes in depths of sediment deposits in combined sewers have also indicated that there is an interaction between the erosion and deposition processes and changes in the mass transport of solids in regions in the overlying flow. A fuller understanding of the interactive phenomena is essential for both sewer sediment management and the minimization of associated pollution from wash-out of solids via CSOs. The paper presents results from the detailed studies in Hildesheim, Germany and those carried out in Dundee, Scotland, investigating the heterogeneity of solids movement with regard to gross solids, erosion of sewer sediments and their interactions with the suspended transport phases and the layer of very dense fluid found to be transported under certain circumstances, near the sediment bed or sewer invert (traditionally called ‘bed-load’).

The transfer of solids in combined sewer networks

Suspended solids are the main vectors of pollution in combined sewer wet weather flows. In spite of being very fine, they decant rather quickly except in the case of light rainfall events rich in organic matter. The part originating from sewer sediment deposits provides a large proportion of organic matter mass. By analysing the content and the volume of sewer deposits at different points from upstream to downstream, it emerges that the main source of this contribution is probably located in man-entry sewers. In one of these, sewer trunk no. 13 in Marseilles, five hundred metres of which were monitored continuously for sediment build-up over three years, the deposit volume grows mainly during certain rainfall events and its surface slope tends to an equilibrium with the (millimetric) particle size. Theoretical bed-load and suspension thresholds have been validated, then analysed for various situations and sections. A typology of the vulnerable areas, in several networks, has been drawn up, as well as a study of shear stress variations during a rainfall event. The sediment deposits seem to occur in particular hydraulic discontinuity zones where transport capacities can drop sharply.

Organic near-bed fluid and particulate transport in combined sewers

Studies in Germany, Belgium, France and Scotland have revealed that there are significant solids transport gradients in the depth of foul and combined sewage flows. Continuous field observations of changes in depths of sediment deposits in combined sewers have also indicated that there is an interaction between the erosion and deposition processes and changes to the mass transport of solids in regions in the overlying flow. A fuller understanding of the interactive phenomena is essential for both sewer sediment management and the minimization of associated pollution from wash-out of solids via CSOs. The paper presents results from the detailed studies in Hildesheim, Germany and those carried out in Dundee, Scotland, investigating the heterogeneity of solids movement with regard to gross solids, erosion of sewer sediments and their interactions with the suspended transport phases and the layer of very dense fluid found to be transported under certain circumstances, near the sediment bed or sewer invert (traditionally called ‘bed-load’).

Location and General Characteristics of Sediment Deposits into Man-Entry Combined Sewers

This study has the following principle aims. – Identifying the contextual elements of sediment deposits which appear as the most important, or, in a way, as required conditions for clogging. It emerges that a weak slope is not a sufficient condition. We show that the main vulnerable sections are:downstream abrupt changes of geometry (the upper ramifications of man-entry sewers, the slope breakdowns, …)downstream flow losses (diffluence, overflows)under downstream influences (confluence, pumping stations, …). – Clearing the general characteristics of these sediment deposits in French man-entry combined sewers. The mean D50 varies from 1mm (Paris) to more than 2mm. The finest deposits are rather specifically located (upstream of local obstacles, or under downstream influences during dry weather - for instance near a pumping station, in very flat sewers -, or downstream from overflows). – Evaluating the representativeness of the results from more accurate studies carried out in particular places, for instance the Marseille No 13 trunk. – Drawing inferences about knowledge improvements and technical means.

Rheological Measurement of the Yield Strength of Combined Sewer Sediment Deposits

A definition for a working value of yield stress for sediment deposits with a cohesive nature is provided through the application of rheometrical techniques. An applied stress technique was utilised to examine the yield characteristics of sixty-one sediment samples obtained from a combined interceptor sewer. Yield strength values obtained were related to the solid/liquid phase relationships for these sediment samples. It is suggested that the yield strength presented can provide a suitable definition for material available for erosion from the sediment bed.

Sediments in Sewers

AbstractA recent survey has suggested that up to 25 000 km of UK sewerage networks may be affected by in‐pipe sediment deposits. Field evidence indicates that, typically, up to 90% of the pollution load discharged from storm sewage overflows may be derived from the erosion of accumulated in‐system sediment, commonly referred to as silt.A sewer flow quality simulation model is being developed under the aegis of the WRc/Water Industry Collaborative River Basin Management research programme. Such a model will enable sewerage engineers and water quality planners to produce more effective designs for sewerage rehabilitation schemes to control river pollution. In order to produce this model it is necessary to understand the nature, characteristics and controlling mechanisms of in‐pipe sediment deposits.Field observations, coupled with sampling and analysis of combined sewer sediment deposits, have produced a five category classification for such sediments. Each category has distinctive characteristics in terms of appearance, composition and polluting potential.