Sediments in sewers

A list of available codes of practice for self-cleansing sewers is presented and a review of appraisals of minimum velocity criterion is summarised. Comparisons of newly developed "minimum velocity" criteria and "minimum shear stress" criterion are presented. Some design charts are also given. These charts are applicable to non-cohesive sediments (typically storm sewers). It appears that sediment size and concentration need to be taken into account, and that a limited depth of sediment bed is recommended for large pipes (diameters > 1000 mm) to maximise their transport capacity.

Most of the estuarine and ocean bottoms are covered with sediments making this the largest habitat on our planet. Grain size data of the estuarine sediments are of great importance in differentiating various depositional microenvironments and also useful for assessing the textural characteristics of the habitat in benthic ecological studies. Here we use grain size analysis of the intertidal surface sediments along the Brunei estuary (Borneo, South East Asia) and the result reveals the dominance of sand fractions, and the percentage of dominance follows the order of sand > clay > silt. The sand size fraction was higher at seaward stations, which were poor in organic matter (<4 %), in contrast to the low-energy landward stations, which comprised a higher proportion of fine-grained (clay and silt) sediments and were rich in organic matter (> 5%). This pattern suggests that the intertidal sediments of the estuary derive from a mixed origin, including continental/marine and terrestrial sources, which vary in degree along the estuarine gradient in relation to hydrodynamic wave/current energy (generally low to high in a seaward direction along the estuary). There was strong negative correlation between the sand fraction and the other sediment variables (silt, clay and organic matter), whereas a positive correlation was observed between organic matter and silt/clay. Univariate (ANOVA) and multivariate (PCA) techniques clearly showed significant spatial differences in the sediment variables among the stations investigated, confirming differential energy conditions at different locations. Cluster analysis and PCA helped to discriminate the station groups along the estuary according to their sediment textural properties. This study also revealed that sediment grain size is a key factor influencing the organic matter accumulation in surface sediments. The organic matter observed in different stations is quite in agreement with the widely accepted view of other researchers from the tropical region that fine grained sediments generally have higher amounts of organic matter than the coarse grained one. The high organic matter at landward stations was found to reflect natural (mangroves) and anthropogenic (pollution) organic input.

The present study was carried out in order to study the textural characteristics of sediments and their seasonal changes along with the Coleroon estuary. Sediment samples were collected at different stations in monsoon, postmonsoon, summer and premonsoon seasons from 2009 to 2010. Spatial variations in grain-size parameters (i.e. grain-size trends) contain information on sediment transport patterns. Analytical procedures have been proposed using the grain-size trends to determine sediment transport pathways. Spatial distribution of sediments clearly indicated more finer particles deposited at mid estuarine region compared to at mouth and freshwater region. Hydrodynamic condition of Coleroon estuarine sediments indicates moderate to high energy condition. The grain size trend analysis indicates the estuarine sediments belong to type-1 trend F, B (finer, better sorted more negative skewed). Clay mineral studies exhibit the observed order of abundance minerals are illite followed by the kaolinite+chlorite, montmorillonite and gibssite. The higher percentage of clay minerals was present at estuary and mouth regions when compared to the freshwater region.

The present study was carried out in order to study the textural characteristics of sediments and their seasonal changes along with the Coleroon estuary. Sediment samples were collected at different stations in monsoon, postmonsoon, summer and premonsoon seasons from 2009 to 2010. Spatial variations in grain-size parameters (i.e. grain-size trends) contain information on sediment transport patterns. Analytical procedures have been proposed using the grain-size trends to determine sediment transport pathways. Spatial distribution of sediments clearly indicated more finer particles deposited at mid estuarine region compared to at mouth and freshwater region. Hydrodynamic condition of Coleroon estuarine sediments indicates moderate to high energy condition. The grain size trend analysis indicates the estuarine sediments belong to type-1 trend F, B (finer, better sorted more negative skewed). Clay mineral studies exhibit the observed order of abundance minerals are illite followed by th...

Sediments are solid, fragmented particulate matter (silt, sand, and gravel), which are transported and deposited by physical processes such as water, wind, and ice. Sediments consist of loose, solid particles originating from the weathering and erosion of rocks, or chemical precipitation from solution, including secretion by organisms in water.

Deposits build up in sewer networks during both dry-weather and storm-water events. Especially in combined sewers, the sediment materials cause various undesirable effects. Flushing devices are able to remove deposits in sewers by generating flushing waves. To optimize the flushing with so called Storage-Volume-Activated-Devices (SVAD) numerical studies were carried out. The objective was to investigate the behaviour of the activated storage-volume of flushing waves on cleaning performance.